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Definitions

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Abbreviations

14 CFRAeronautics and Space

CHAPTER IFEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION

SUBCHAPTER A -- DEFINITIONS

PART 1 -- DEFINITIONS AND ABBREVIATIONS

FAR 1.1 – 1.3 Currency 6/6/02Page 1

§1.1 General Definitions.As used in Subchapters A through K of this chapter, unless the context requires otherwise:

Administrator means the Federal Aviation Administrator or any person to whom he has delegated hisauthority in the matter concerned.

Aerodynamic coefficients means non-dimensional coefficients for aerodynamic forces and moments.

Air carrier means a person who undertakes directly by lease, or other arrangement, to engage in airtransportation.

Air commerce means interstate, overseas, or foreign air commerce or the transportation of mail by aircraftor any operation or navigation of aircraft within the limits of any Federal airway or any operation ornavigation of aircraft which directly affects, or which may endanger safety in, interstate, overseas, orforeign air commerce.

Aircraft means a device that is used or intended to be used for flight in the air.

Aircraft engine means an engine that is used or intended to be used for propelling aircraft. It includesturbosuperchargers, appurtenances, and accessories necessary for its functioning, but does not includepropellers.

Airframe means the fuselage, booms, nacelles, cowlings, fairings, airfoil surfaces (including rotors butexcluding propellers and rotating airfoils of engines), and landing gear of an aircraft and their accessoriesand controls.

Airplane means an engine-driven fixed-wing aircraft heavier than air, that is supported in flight by thedynamic reaction of the air against its wings.

Airport means an area of land or water that is used or intended to be used for the landing and takeoff ofaircraft, and includes its buildings and facilities, if any.

Airship means an engine-driven lighter-than-air aircraft that can be steered.

Air traffic means aircraft operating in the air or on an airport surface, exclusive of loading ramps andparking areas.

Air traffic clearance means an authorization by air traffic control, for the purpose of preventing collisionbetween known aircraft, for an aircraft to proceed under specified traffic conditions within controlledairspace.

Air traffic control means a service operated by appropriate authority to promote the safe, orderly, andexpeditious flow of air traffic.

Air transportation means interstate, overseas, or foreign air transportation or the transportation of mail byaircraft.

Alert Area. An alert area is established to inform pilots of a specific area wherein a high volume of pilottraining or an unusual type of aeronautical activity is conducted.

Alternate airport means an airport at which an aircraft may land if a landing at the intended airportbecomes inadvisable.






Altitude engine means a reciprocating aircraft engine having a rated takeoff power that is producible fromsea level to an established higher altitude.

Appliance means any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory,including communications equipment, that is used or intended to be used in operating or controlling anaircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine, orpropeller.

Approved, unless used with reference to another person, means approved by the Administrator.

Area navigation (RNAV) means a method of navigation that permits aircraft operations on any desiredcourse within the coverage of station-referenced navigation signals or within the limits of self-containedsystem capability.

Area navigation low route means an area navigation route within the airspace extending upward from1,200 feet above the surface of the earth to, but not including, 18,000 feet MSL.

Area navigation high route means an area navigation route within the airspace extending upward from,and including, 18,000 feet MSL to flight level 450.

Armed Forces means the Army, Navy, Air Force, Marine Corps, and Coast Guard, including their regularand reserve components and members serving without component status.

Autorotation means a rotorcraft flight condition in which the lifting rotor is driven entirely by action of theair when the rotorcraft is in motion.

Auxiliary rotor means a rotor that serves either to counteract the effect of the main rotor torque on arotorcraft or to maneuver the rotorcraft about one or more of its three principal axes.

Balloon means a lighter-than-air aircraft that is not engine driven, and that sustains flight through the useof either gas buoyancy or an airborne heater.

Brake horsepower means the power delivered at the propeller shaft (main drive or main output) of anaircraft engine.

Calibrated airspeed means the indicated airspeed of an aircraft, corrected for position and instrumenterror. Calibrated airspeed is equal to true airspeed in standard atmosphere at sea level.

Canard means the forward wing of a canard configuration and may be a fixed, movable, or variablegeometry surface, with or without control surfaces.

Canard configuration means a configuration in which the span of the forward wing is substantially lessthan that of the main wing.

Category:(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means a broadclassification of aircraft. Examples include: airplane; rotorcraft; glider; and lighter-than-air; and(2) As used with respect to the certification of aircraft, means a grouping of aircraft based upon intendeduse or operating limitations. Examples include: transport, normal, utility, acrobatic, limited, restricted, andprovisional.






Category A, with respect to transport category rotorcraft, means multiengine rotorcraft designed withengine and system isolation features specified in Part 29 and utilizing scheduled takeoff and landingoperations under a critical engine failure concept which assures adequate designated surface area andadequate performance capability for continued safe flight in the event of engine failure.

Category B, with respect to transport category rotorcraft, means single-engine or multiengine rotorcraftwhich do not fully meet all Category A standards. Category B rotorcraft have no guaranteed stay-upability in the event of engine failure and unscheduled landing is assumed.

Category II operations, with respect to the operation of aircraft, means a straight-in ILS approach to therunway of an airport under a Category II ILS instrument approach procedure issued by the Administratoror other appropriate authority.

Category III operations, with respect to the operation of aircraft, means an ILS approach to, and landingon, the runway of an airport using a Category III ILS instrument approach procedure issued by theAdministrator or other appropriate authority.

Category IIIa operations, an ILS approach and landing with no decision height (DH), or a DH below 100feet (30 meters), and controlling runway visual range not less than 700 feet (200 meters).

Category IIIb operations, an ILS approach and landing with no DH, or with a DH below 50 feet (15meters), and controlling runway visual range less than 700 feet (200 meters), but not less than 150 feet(50 meters).

Category IIIc operations, an ILS approach and landing with no DH and no runway visual range limitation.

Ceiling means the height above the earth's surface of the lowest layer of clouds or obscuring phenomenathat is reported as "broken", "overcast", or "obscuration", and not classified as "thin" or "partial".

Civil aircraft means aircraft other than public aircraft.

Class:(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means aclassification of aircraft within a category having similar operating characteristics. Examples include:single engine; multiengine; land; water; gyroplane; helicopter; airship; and free balloon; and(2) As used with respect to the certification of aircraft, means a broad grouping of aircraft having similarcharacteristics of propulsion, flight, or landing. Examples include: airplane; rotorcraft; glider; balloon;landplane; and seaplane.

Clearway means:(1) For turbine engine powered airplanes certificated after August 29, 1959, an area beyond the runway,not less than 500 feet wide, centrally located about the extended centerline of the runway, and under thecontrol of the airport authorities. The clearway is expressed in terms of a clearway plane, extending fromthe end of the runway with an upward slope not exceeding 1.25 percent, above which no object nor anyterrain protrudes. However, threshold lights may protrude above the plane if their height above the end ofthe runway is 26 inches or less and if they are located to each side of the runway.(2) For turbine engine powered airplanes certificated after September 30, 1958, but before August 30,1959, an area beyond the takeoff runway extending no less than 300 feet on either side of the extendedcenterline of the runway, at an elevation no higher than the elevation of the end of the runway, clear of allfixed obstacles, and under the control of the airport authorities.






Climbout speed, with respect to rotorcraft, means a referenced airspeed which results in a flight pathclear of the height-velocity envelope during initial climbout.

Commercial operator means a person who, for compensation or hire, engages in the carriage by aircraftin air commerce of persons or property, other than as an air carrier or foreign air carrier or under theauthority of Part 375 of this title. Where it is doubtful that an operation is for "compensation or hire", thetest applied is whether the carriage by air is merely incidental to the person's other business or is, in itself,a major enterprise for profit.

Controlled airspace means an airspace of defined dimensions within which air traffic control service isprovided to IFR flights and to VFR flights in accordance with the airspace classification.Note: Controlled airspace is a generic term that covers Class A, Class B, Class C, Class D, and Class Eairspace.

Controlled Firing Area. A controlled firing area is established to contain activities, which if not conductedin a controlled environment, would be hazardous to nonparticipating aircraft.

Crewmember means a person assigned to perform duty in an aircraft during flight time.

Critical altitude means the maximum altitude at which, in standard atmosphere, it is possible to maintain,at a specified rotational speed, a specified power or a specified manifold pressure. Unless otherwisestated, the critical altitude is the maximum altitude at which it is possible to maintain, at the maximumcontinuous rotational speed, one of the following:(1) The maximum continuous power, in the case of engines for which this power rating is the same at sealevel and at the rated altitude.(2) The maximum continuous rated manifold pressure, in the case of engines, the maximum continuouspower of which is governed by a constant manifold pressure.

Critical engine means the engine whose failure would most adversely affect the performance or handlingqualities of an aircraft.

Decision height, with respect to the operation of aircraft, means the height at which a decision must bemade, during an ILS or PAR instrument approach, to either continue the approach or to execute a missedapproach.

Equivalent airspeed means the calibrated airspeed of an aircraft corrected for adiabatic compressible flowfor the particular altitude. Equivalent airspeed is equal to calibrated airspeed in standard atmosphere atsea level.

Extended over-water operation means --(1) With respect to aircraft other than helicopters, an operation over water at a horizontal distance of morethan 50 nautical miles from the nearest shoreline; and(2) With respect to helicopters, an operation over water at a horizontal distance of more than 50 nauticalmiles from the nearest shoreline and more than 50 nautical miles from an off-shore heliport structure.

External load means a load that is carried, or extends, outside of the aircraft fuselage.

External-load attaching means means the structural components used to attach an external load to anaircraft, including external-load containers, the backup structure at the attachment points, and any quick-release device used to jettison the external load.






Fireproof --(1) With respect to materials and parts used to confine fire in a designated fire zone, means the capacityto withstand at least as well as steel in dimensions appropriate for the purpose for which they are used,the heat produced when there is a severe fire of extended duration in that zone; and(2) With respect to other materials and parts, means the capacity to withstand the heat associated withfire at least as well as steel in dimensions appropriate for the purpose for which they are used.

Fire resistant --(1) With respect to sheet or structural members means the capacity to withstand the heat associated withfire at least as well as aluminum alloy in dimensions appropriate for the purpose for which they are used;and(2) With respect to fluid-carrying lines, fluid system parts, wiring, air ducts, fittings, and powerplantcontrols, means the capacity to perform the intended functions under the heat and other conditions likelyto occur when there is a fire at the place concerned.

Flame resistant means not susceptible to combustion to the point of propagating a flame, beyond safelimits, after the ignition source is removed.

Flammable, with respect to a fluid or gas, means susceptible to igniting readily or to exploding.

Flap extended speed means the highest speed permissible with wing flaps in a prescribed extendedposition.

Flash resistant means not susceptible to burning violently when ignited.

Flightcrew member means a pilot, flight engineer, or flight navigator assigned to duty in an aircraft duringflight time.

Flight level means a level of constant atmospheric pressure related to a reference datum of 29.92 inchesof mercury. Each is stated in three digits that represent hundreds of feet. For example, flight level 250represents a barometric altimeter indication of 25,000 feet; flight level 255, an indication of 25,500 feet.

Flight plan means specified information, relating to the intended flight of an aircraft, that is filed orally or inwriting with air traffic control.

Flight time means:(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight andends when the aircraft comes to rest after landing; or(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for thepurpose of flight and ends when the glider comes to rest after landing.

Flight visibility means the average forward horizontal distance, from the cockpit of an aircraft in flight, atwhich prominent unlighted objects may be seen and identified by day and prominent lighted objects maybe seen and identified by night.

Foreign air carrier means any person other than a citizen of the United States, who undertakes directly,by lease or other arrangement, to engage in air transportation.

Foreign air commerce means the carriage by aircraft of persons or property for compensation or hire, orthe carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or furtherance of abusiness or vocation, in commerce between a place in the United States and any place outside thereof;






whether such commerce moves wholly by aircraft or partly by aircraft and partly by other forms oftransportation.

Foreign air transportation means the carriage by aircraft of persons or property as a common carrier forcompensation or hire, or the carriage of mail by aircraft, in commerce between a place in the UnitedStates and any place outside of the United States, whether that commerce moves wholly by aircraft orpartly by aircraft and partly by other forms of transportation.

Forward wing means a forward lifting surface of a canard configuration or tandem-wing configurationairplane. The surface may be a fixed, movable, or variable geometry surface, with or without controlsurfaces.

Glider means a heavier-than-air aircraft, that is supported in flight by the dynamic reaction of the airagainst its lifting surfaces and whose free flight does not depend principally on an engine.

Ground visibility means prevailing horizontal visibility near the earth's surface as reported by the UnitedStates National Weather Service or an accredited observer.

Go-around power or thrust setting means the maximum allowable in-flight power or thrust settingidentified in the performance data.

Gyrodyne means a rotorcraft whose rotors are normally engine-driven for takeoff, hovering, and landing,and for forward flight through part of its speed range, and whose means of propulsion, consisting usuallyof conventional propellers, is independent of the rotor system.

Gyroplane means a rotorcraft whose rotors are not engine-driven, except for initial starting, but are madeto rotate by action of the air when the rotorcraft is moving; and whose means of propulsion, consistingusually of conventional propellers, is independent of the rotor system.

Helicopter means a rotorcraft that, for its horizontal motion, depends principally on its engine-drivenrotors.

Heliport means an area of land, water, or structure used or intended to be used for the landing andtakeoff of helicopters.

Idle thrust means the jet thrust obtained with the engine power control level set at the stop for the leastthrust position at which it can be placed.

IFR conditions means weather conditions below the minimum for flight under visual flight rules.

IFR over-the-top, with respect to the operation of aircraft, means the operation of an aircraft over-the-topon an IFR flight plan when cleared by air traffic control to maintain "VFR conditions" or "VFR conditionson top".

Indicated airspeed means the speed of an aircraft as shown on its pitot static airspeed indicator calibratedto reflect standard atmosphere adiabatic compressible flow at sea level uncorrected for airspeed systemerrors.

Instrument means a device using an internal mechanism to show visually or aurally the attitude, altitude,or operation of an aircraft or aircraft part. It includes electronic devices for automatically controlling anaircraft in flight.






Interstate air commerce means the carriage by aircraft of persons or property for compensation or hire, orthe carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or furtherance of abusiness or vocation, in commerce between a place in any State of the United States, or the District ofColumbia, and a place in any other State of the United States, or the District of Columbia; or betweenplaces in the same State of the United States through the airspace over any place outside thereof; orbetween places in the same territory or possession of the United States, or the District of Columbia.

Interstate air transportation means the carriage by aircraft of persons or property as a common carrier forcompensation or hire, or the carriage of mail by aircraft in commerce:(1) Between a place in a State or the District of Columbia and another place in another State or theDistrict of Columbia;(2) Between places in the same State through the airspace over any place outside that State; or(3) Between places in the same possession of the United States;Whether that commerce moves wholly by aircraft of partly by aircraft and partly by other forms oftransportation.

Intrastate air transportation means the carriage of persons or property as a common carrier forcompensation or hire, by turbojet-powered aircraft capable of carrying thirty or more persons, whollywithin the same State of the United States.

Kite means a framework, covered with paper, cloth, metal, or other material, intended to be flown at theend of a rope or cable, and having as its only support the force of the wind moving past its surfaces.

Landing gear extended speed means the maximum speed at which an aircraft can be safely flown withthe landing gear extended.

Landing gear operating speed means the maximum speed at which the landing gear can be safelyextended or retracted.

Large aircraft means aircraft of more than 12,500 pounds, maximum certificated takeoff weight.

Lighter-than-air aircraft means aircraft that can rise and remain suspended by using contained gasweighing less than the air that is displaced by the gas.

Load factor means the ratio of a specified load to the total weight of the aircraft. The specified load isexpressed in terms of any of the following: aerodynamic forces, inertia forces, or ground or waterreactions.

Long-range communication system (LRCS). A system that uses satellite relay, data link, high frequency,or another approved communication system which extends beyond line of sight.

Long-range navigation system (LRNS). An electronic navigation unit that is approved for use underinstrument flight rules as a primary means of navigation, and has at least one source of navigationalinput, such as inertial navigation system, global positioning system, Omega/very low frequency, or LoranC.

Mach number means the ratio of true airspeed to the speed of sound.

Main rotor means the rotor that supplies the principal lift to a rotorcraft.

Maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, butexcludes preventive maintenance.






Major alteration means an alteration not listed in the aircraft, aircraft engine, or propeller specifications --(1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation,flight characteristics, or other qualities affecting airworthiness; or(2) That is not done according to accepted practices or cannot be done by elementary operations.

Major repair means a repair:(1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance,powerplant operation, flight characteristics, or other qualities affecting airworthiness; or(2) That is not done according to accepted practices or cannot be done by elementary operations.

Manifold pressure means absolute pressure as measured at the appropriate point in the induction systemand usually expressed in inches of mercury.

Maximum speed for stability characteristics, VFC/MFC means a speed that may not be less than a speedmidway between maximum operating limit speed (VMO/MMO) and demonstrated flight diving speed(VDF/MDF), except that, for altitudes where the Mach number is the limiting factor, MFC need not exceedthe Mach number at which effective speed warning occurs.

Medical certificate means acceptable evidence of physical fitness on a form prescribed by theAdministrator.

Military operations area. A military operations area (MOA) is airspace established outside Class Aairspace to separate or segregate certain nonhazardous military activities from IFR Traffic and to identifyfor VFR traffic where theses activities are conducted.

Minimum descent altitude means the lowest altitude, expressed in feet above mean sea level, to whichdescent is authorized on final approach or during circle-to-land maneuvering in execution of a standardinstrument approach procedure, where no electronic glide slope is provided.

Minor alteration means an alteration other than a major alteration.

Minor repair means a repair other than a major repair.

Navigable airspace means airspace at and above the minimum flight altitudes prescribed by or under thischapter, including airspace needed for safe takeoff and landing.

Night means the time between the end of evening civil twilight and the beginning of morning civil twilight,as published in the American Air Almanac, converted to local time.

Nonprecision approach procedure means a standard instrument approach procedure in which noelectronic glide slope is provided.

Operate, with respect to aircraft, means use, cause to use or authorize to use aircraft, for the purpose(except as provided in §91.13 of this chapter) of air navigation including the piloting of aircraft, with orwithout the right of legal control (as owner, lessee, or otherwise).

Operational control, with respect to a flight, means the exercise of authority over initiating, conducting orterminating a flight.

Overseas air commerce means the carriage by aircraft of persons or property for compensation or hire, orthe carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or furtherance of abusiness or vocation, in commerce between a place in any State of the United States, or the District of






Columbia, and any place in a territory or possession of the United States; or between a place in a territoryor possession of the United States, and a place in any other territory or possession of the United States.

Overseas air transportation means the carriage by aircraft of persons or property as a common carrier forcompensation or hire, or the carriage of mail by aircraft, in commerce:(1) Between a place in a State or the District of Columbia and a place in a possession of the UnitedStates; or(2) Between a place in a possession of the United States and a place in another possession of the UnitedStates; whether that commerce moves wholly by aircraft or partly by aircraft and partly by other forms oftransportation.

Over-the-top means above the layer of clouds or other obscuring phenomena forming the ceiling.

Parachute means a device used or intended to be used to retard the fall of a body or object through theair.

Person means an individual, firm, partnership, corporation, company, association, joint-stock association,or governmental entity. It includes a trustee, receiver, assignee, or similar representative of any of them.

Pilotage means navigation by visual reference to landmarks.

Pilot in command means the person who:(1) Has final authority and responsibility for the operation and safety of the flight;(2) Has been designated as pilot in command before or during the flight; and(3) Holds the appropriate category, class, and type rating, if appropriate, for the conduct of the flight.

Pitch setting means the propeller blade setting as determined by the blade angle measured in a manner,and at a radius, specified by the instruction manual for the propeller.

Positive control means control of all air traffic, within designated airspace, by air traffic control.

Powered-lift means a heavier-than-air aircraft capable of vertical takeoff, vertical landing, and low speedflight that depends principally on engine-driven lift devices or engine thrust for lift during these flightregimes and on nonrotating airfoil(s) for lift during horizontal flight.

Precision approach procedure means a standard instrument approach procedure in which an electronicglide slope is provided, such as ILS and PAR.

Preventive maintenance means simple or minor preservation operations and the replacement of smallstandard parts not involving complex assembly operations.

Prohibited area. A prohibited area is airspace designated under part 73 within which no person mayoperate an aircraft without the permission of the using agency.

Propeller means a device for propelling an aircraft that has blades on an engine-driven shaft and that,when rotated, produces by its action on the air, a thrust approximately perpendicular to its plane ofrotation. It includes control components normally supplied by its manufacturer, but does not include mainand auxiliary rotors or rotating airfoils of engines.

Public aircraft means an aircraft used only for the United States Government, or owned and operated(except for commercial purposes), or exclusively leased for at least 90 continuous days, by a government(except the United States Government), including a State, the District of Columbia, or a territory or






possession of the United States, or political subdivision of that government; but does not include agovernment-owned aircraft transporting property for commercial purposes, or transporting passengersother than transporting (for other than commercial purposes) crewmembers or other persons aboard theaircraft whose presence is required to perform, or is associated with the performance of, a governmentalfunction such as firefighting, search and rescue, law enforcement, aeronautical research, or biological orgeological resource management; or transporting (for other than commercial purposes) persons aboardthe aircraft if the aircraft is operated by the Armed Forces or an intelligence agency of the United States.An aircraft described in the preceding sentence shall, notwithstanding any limitation relating to use of theaircraft for commercial purposes, be considered to be a public aircraft for the purposes of this Chapterwithout regard to whether the aircraft is operated by a unit of government on behalf of another unit ofgovernment, pursuant to a cost reimbursement agreement between such units of government, if the unitof government on whose behalf the operation is conducted certifies to the Administrator of the FederalAviation Administration that the operation was necessary to respond to a significant and imminent threatto life or property (including natural resources) and that no service by a private operator was reasonablyavailable to meet the threat.

Rated 30-second OEI power, with respect to rotorcraft turbine engines, means the approved brakehorsepower developed under static conditions at specified altitudes and temperatures within the operatinglimitations established for the engine under part 33 of this chapter, for continued one-flight operation afterthe failure of one engine in multiengine rotorcraft, limited to three periods of use no longer than 30seconds each in any one flight, and followed by mandatory inspection and prescribed maintenanceaction.

Rated 2-minute OEI power, with respect to rotorcraft turbine engines, means the approved brakehorsepower developed under static conditions at specified altitudes and temperatures within the operatinglimitations established for the engine under part 33 of this chapter, for continued one-flight operation afterthe failure of one engine in multiengine rotorcraft, limited to three periods of use no longer than 2 minuteseach in any one flight, and followed by mandatory inspection and prescribed maintenance action.

Rated continuous OEI power, with respect to rotorcraft turbine engines, means the approved brakehorsepower developed under static conditions at specified altitudes and temperatures within the operatinglimitations established for the engine under Part 33 of this chapter, and limited in use to the time requiredto complete the flight after the failure of one engine of a multiengine rotorcraft.

Rated maximum continuous augmented thrust, with respect to turbojet engine type certification, meansthe approved jet thrust that is developed statically or in flight, in standard atmosphere at a specifiedaltitude, with fluid injection or with the burning of fuel in a separate combustion chamber, within theengine operating limitations established under Part 33 of this chapter, and approved for unrestrictedperiods of use.

Rated maximum continuous power, with respect to reciprocating, turbopropeller, and turboshaft engines,means the approved brake horsepower that is developed statically or in flight, in standard atmosphere ata specified altitude, within the engine operating limitations established under Part 33, and approved forunrestricted periods of use.

Rated maximum continuous thrust, with respect to turbojet engine type certification, means the approvedjet thrust that is developed statically or in flight, in standard atmosphere at a specified altitude, withoutfluid injection and without the burning of fuel in a separate combustion chamber, within the engineoperating limitations established under Part 33 of this chapter, and approved for unrestricted periods ofuse.






Rated takeoff augmented thrust, with respect to turbojet engine type certification, means the approved jetthrust that is developed statically under standard sea level conditions, with fluid injection or with theburning of fuel in a separate combustion chamber, within the engine operating limitations establishedunder Part 33 of this chapter, and limited in use to periods of not over 5 minutes for takeoff operation.

Rated takeoff power, with respect to reciprocating, turbopropeller, and turboshaft engine type certification,means the approved brake horsepower that is developed statically under standard sea level conditions,within the engine operating limitations established under Part 33, and limited in use to periods of not over5 minutes for takeoff operation.

Rated takeoff thrust, with respect to turbojet engine type certification, means the approved jet thrust thatis developed statically under standard sea level conditions, without fluid injection and without the burningof fuel in a separate combustion chamber, within the engine operating limitations established under Part33 of this chapter, and limited in use to periods of not over 5 minutes for takeoff operation.

Rated 30-minute OEI power, with respect to rotorcraft turbine engines, means the approved brakehorsepower developed under static conditions at specified altitudes and temperatures within the operatinglimitations established for the engine under Part 33 of this chapter, and limited in use to a period of notmore than 30 minutes after the failure of one engine of a multiengine rotorcraft.

Rated 2 1/2-minute OEI power, with respect to rotorcraft turbine engines, means the approved brakehorsepower developed under static conditions at specified altitudes and temperatures within the operatinglimitations established for the engine under Part 33 of this chapter, and limited in use to a period of notmore than 2 1/2 minutes after the failure of one engine of a multiengine rotorcraft.

Rating means a statement that, as a part of a certificate, sets forth special conditions, privileges, orlimitations.

Reporting point means a geographical location in relation to which the position of an aircraft is reported.

Restricted area. A restricted area is airspace designated under Part 73 within which the flight of aircraft,while not wholly prohibited, is subject to restriction.

RNAV way point (W/P) means a predetermined geographical position used for route or instrumentapproach definition or progress reporting purposes that is defined relative to a VORTAC station position.

Rocket means an aircraft propelled by ejected expanding gases generated in the engine from self-contained propellants and not dependent on the intake of outside substances. It includes any part whichbecomes separated during the operation.

Rotorcraft means a heavier-than-air aircraft that depends principally for its support in flight on the liftgenerated by one or more rotors.

Rotorcraft-load combination means the combination of a rotorcraft and an external-load, including theexternal-load attaching means. Rotorcraft-load combinations are designated as Class A, Class B, ClassC, and Class D, as follows:(1) Class A rotorcraft-load combination means one in which the external load cannot move freely, cannotbe jettisoned, and does not extend below the landing gear.(2) Class B rotorcraft-load combination means one in which the external load is jettisonable and is liftedfree of land or water during the rotorcraft operation.(3) Class C rotorcraft-load combination means one in which the external load is jettisonable and remainsin contact with land or water during the rotorcraft operation.






(4) Class D rotorcraft-load combination means one in which the external-load is other than a Class A, B,or C and has been specifically approved by the Administrator for that operation.

Route segment means a part of a route. Each end of that part is identified by:(1) A continental or insular geographical location; or(2) A point at which a definite radio fix can be established.

Sea level engine means a reciprocating aircraft engine having a rated takeoff power that is producibleonly at sea level.

Second in command means a pilot who is designated to be second in command of an aircraft during flighttime.

Show, unless the context otherwise requires, means to show to the satisfaction of the Administrator.

Small aircraft means aircraft of 12,500 pounds or less, maximum certificated takeoff weight.

Special VFR conditions mean meteorological conditions that are less than those required for basic VFRflight in controlled airspace and in which some aircraft are permitted flight under visual flight rules.

Special VFR operations means aircraft operating in accordance with clearances within controlled airspacein meteorological conditions less than the basic VFR weather minima. Such operations must berequested by the pilot and approved by ATC.

Standard atmosphere means the atmosphere defined in U.S. Standard Atmosphere, 1962 (Geopotentialaltitude tables).

Stopway means an area beyond the takeoff runway, no less wide than the runway and centered upon theextended centerline of the runway, able to support the airplane during an aborted takeoff, without causingstructural damage to the airplane, and designated by the airport authorities for use in decelerating theairplane during an aborted takeoff.

Takeoff power:(1) With respect to reciprocating engines, means the brake horsepower that is developed under standardsea level conditions, and under the maximum conditions of crankshaft rotational speed and enginemanifold pressure approved for the normal takeoff, and limited in continuous use to the period of timeshown in the approved engine specification; and(2) With respect to turbine engines, means the brake horsepower that is developed under staticconditions at a specified altitude and atmospheric temperature, and under the maximum conditions ofrotor shaft rotational speed and gas temperature approved for the normal takeoff, and limited incontinuous use to the period of time shown in the approved engine specification.

Takeoff safety speed means a referenced airspeed obtained after lift-off at which the required one-engine-inoperative climb performance can be achieved.

Takeoff thrust, with respect to turbine engines, means the jet thrust that is developed under staticconditions at a specific altitude and atmospheric temperature under the maximum conditions of rotorshaftrotational speed and gas temperature approved for the normal takeoff, and limited in continuous use tothe period of time shown in the approved engine specification.

Tandem wing configuration means a configuration having two wings of similar span, mounted in tandem.






TCAS I means a TCAS that utilizes interrogations of, and replies from, airborne radar beacontransponders and provides traffic advisories to the pilot.

TCAS II means a TCAS that utilizes interrogations of, and replies from airborne radar beacontransponders and provides traffic advisories and resolution advisories in the vertical plane.

TCAS III means a TCAS that utilizes interrogation of, and replies from, airborne radar beacontransponders and provides traffic advisories and resolution advisories in the vertical and horizontal planesto the pilot.

Time in service, with respect to maintenance time records, means the time from the moment an aircraftleaves the surface of the earth until it touches it at the next point of landing.

True airspeed means the airspeed of an aircraft relative to undisturbed air. True airspeed is equal toequivalent airspeed multiplied by (?0/?) 1/2.

Traffic pattern means the traffic flow that is prescribed for aircraft landing at, taxiing on, or taking off from,an airport.

Type:(1) As used with respect to the certification, ratings, privileges, and limitations of airmen, means a specificmake and basic model of aircraft, including modifications thereto that do not change its handling or flightcharacteristics. Examples include: DC-7, 1049, and F-27; and(2) As used with respect to the certification of aircraft, means those aircraft which are similar in design.Examples include: DC-7 and DC-7C; 1049G and 1049H; and F-27 and F-27F.(3) As used with respect to the certification of aircraft engines means those engines which are similar indesign. For example, JT8D and JT8D-7 are engines of the same type, and JT9D-3A and JT9D-7 areengines of the same type.

United States, in a geographical sense, means (1) the States, the District of Columbia, Puerto Rico, andthe possessions, including the territorial waters, and (2) the airspace of those areas.

United States air carrier means a citizen of the United States who undertakes directly by lease, or otherarrangement, to engage in air transportation.

VFR over-the-top, with respect to the operation of aircraft, means the operation of an aircraft over-the-topunder VFR when it is not being operated on an IFR flight plan.

Warning area. A warning area is airspace of defined dimensions, extending from 3 nautical miles outwardfrom the coast of the United States, that contains activity that may be hazardous to nonparticipatingaircraft. The purpose of such warning areas is to warn nonparticipating pilots of the potential danger. Awarning area may be located over domestic or international waters or both.

Winglet or tip fin means an out-of-plane surface extending from a lifting surface. The surface may or maynot have control surfaces.

§1.2 Abbreviations and Symbols.In Subchapters A through K of this chapter:

AGL means above ground level.ALS means approach light system.ASR means airport surveillance radar.






ATC means air traffic control.CAS means calibrated airspeed.CAT II means Category II.CONSOL or CONSOLAN means a kind of low or medium frequency long range navigational aid.DH means decision height.DME means distance measuring equipment compatible with TACAN.EAS means equivalent airspeed.FAA means Federal Aviation Administration.FM means fan marker.GS means glide slope.HIRL means high-intensity runway light system.IAS means indicated airspeed.ICAO means International Civil Aviation Organization.IFR means instrument flight rules.ILS means instrument landing system.IM means ILS inner marker.INT means intersection.LDA means localizer-type directional aid.LFR means low-frequency radio range.LMM means compass locator at middle marker.LOC means ILS localizer.LOM means compass locator at outer marker.M means mach number.MAA means maximum authorized IFR altitude.MALS means medium intensity approach light system.MALSR means medium intensity approach light system with runway alignment indicator lights.MCA means minimum crossing altitude.MDA means minimum descent altitude.MEA means minimum en route IFR altitude.MM means ILS middle marker.MOCA means minimum obstruction clearance altitude.MRA means minimum reception altitude.MSL means mean sea level.NDB(ADF) means nondirectional beacon (automatic direction finder).NOPT means no procedure turn required.OEI means one engine inoperative.OM means ILS outer marker.PAR means precision approach radar.RAIL means runway alignment indicator light system.RBN means radio beacon.RCLM means runway centerline marking.RCLS means runway centerline light system.REIL means runway end identification lights.‘RR" means low or medium frequency radio range station.RVR means runway visual range as measured in the touchdown zone area.SALS means short approach light system.SSALS means simplified short approach light system.SSALSR means simplified short approach light system with runway alignment indicator lights.TACAN means ultra-high frequency tactical air navigational aid.TAS means true airspeed.TCAS means a traffic alert and collision avoidance system.TDZL means touchdown zone lights.TVOR means very high frequency terminal omnirange station.






VA means design maneuvering speed.VB means design speed for maximum gust intensity.VC means design cruising speed.VD means design diving speed.VDF/MDF means demonstrated flight diving speed.VEF means the speed at which the critical engine is assumed to fail during takeoff.VF means design flap speed.VFC/MFC means maximum speed for stability characteristics.VFE means maximum flap extended speed.VH means maximum speed in level flight with maximum continuous power.VLE means maximum landing gear extended speed.VLO means maximum landing gear operating speed.VLOF means lift-off speed.VMC means minimum control speed with the critical engine inoperative.VMO/MMO means maximum operating limit speed.VMU means minimum unstick speed.VNE means never-exceed speed.VNO means maximum structural cruising speed.VR means rotation speed.VS means the stalling speed or the minimum steady flight speed at which the airplane is controllable.VS0 means the stalling speed or the minimum steady flight speed in the landing configuration.VS1 means the stalling speed or the minimum steady flight speed obtained in a specific configuration.VTOSS means takeoff safety speed for Category A rotorcraft.VX means speed for best angle of climb.VY means speed for best rate of climb.V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., applybrakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1

also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which thepilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoffdistance.V2 means takeoff safety speed.V2 min means minimum takeoff safety speed.VFR means visual flight rules.VHF means very high frequency.VOR means very high frequency omnirange station.VORTAC means collocated VOR and TACAN.

§1.3 Rules of Construction.(a) In Subchapters A through K of this chapter, unless the context requires otherwise:(1) Words importing the singular include the plural;(2) Words importing the plural include the singular; and(3) Words importing the masculine gender include the feminine.(b) In Subchapters A through K of this chapter, the word:(1) Shall is used in an imperative sense;(2) May is used in a permissive sense to state authority or permission to do the act prescribed, and thewords "no person may * * *" or "a person may not * * *" mean that no person is required, authorized, orpermitted to do the act prescribed; and(3) Includes means "includes but is not limited to".

v

Units of Measurement° degree (temperature)deg degree (angle)deg/s degrees per secondft feetft/min feet per minuteft/s feet per secondhPa hectoPascalhr hourin inchinHg inches of mercurykg kilogramkn knotm metermbar millibarmi milemin minutenm nautical milesec second

AcronymsADI Attitude Direction IndicatorAFM Approved Flight ManualAGL above ground levelAOA angle of attackASRS Aviation Safety Reporting SystemATC air traffic controlCAT clear air turbulenceCFIT Controlled Flight Into TerrainCG center of gravityECAMS Electronic Centralized Aircraft Monitoring SystemEICAS Engine Indicating and Crew Alerting SystemFAA Federal Aviation AdministrationICAO International Civil Aviation OrganizationILS Instrument Landing SystemIMC instrument meteorological conditionsMAC mean aerodynamic chordMSL mean sea levelNASA National Aeronautics Space AdministrationNTSB National Transportation Safety BoardPF pilot flyingPFD Primary Flight DisplayPNF pilot not flyingRTO rejected takeoffVMC visual meteorological conditionsVSI Vertical Speed Indicator

REFERENCE

vii

Airplane Upset Recovery Glossary

Certain definitions are needed to explain the con-cepts discussed in this training aid. Some of thedefinitions are from regulatory documents or otherreferences, and some are defined in the aid.

Airplane UpsetAn airplane in flight unintentionally exceedingthe parameters normally experienced in line op-erations or training:• Pitch attitude greater than 25 deg, nose up.• Pitch attitude greater than 10 deg, nose down.• Bank angle greater than 45 deg.• Within the above parameters, but flying at

airspeeds inappropriate for the conditions.

Altitude (USA)The height of a level, point, or object measuredin feet above ground level (AGL) or from meansea level (MSL).1. MSL altitude – Altitude expressed in feet mea-

sured from mean sea level.2. AGL altitude – Altitude expressed in feet mea-

sured above ground level.3. Indicated altitude – The altitude as shown by

an altimeter. On a pressure or barometricaltimeter, it is altitude as shown uncorrectedfor instrument error and uncompensated forvariation from standard atmosphericconditions.

Altitude (ICAO)The vertical distance of a level, a point, or anobject considered as a point, measured from meansea level.

Angle of Attack (AOA)Angle of attack is the angle between the oncomingair or relative wind, and some reference line on theairplane or wing.

Autoflight SystemsThe autopilot, autothrottle, and all related sys-tems that perform flight management andguidance.

CamberThe amount of curvature evident in an airfoil shape.

CeilingThe heights above the Earth’s surface of the lowestlayer of clouds or obscuring phenomena that arereported as “broken,” “overcast,” or “obscuration,”and not classified as “thin” or “partial.”

Clear Air Turbulence (CAT)High-level turbulence (normally above 15,000 ftabove sea level) not associated with cumuliformcloudiness, including thunderstorms.

Controlled Flight into Terrain (CFIT)An event where a mechanically normally function-ing airplane is inadvertently flown into the ground,water, or an obstacle.

DihedralThe positive angle formed between the lateral axisof an airplane and a line that passes through thecenter of the wing.

EnergyThe capacity to do work.

Energy StateHow much of each kind of energy (kinetic, poten-tial, or chemical) the airplane has available at anygiven time.

Flight Crew or Flight Crew MemberA pilot, first officer, flight engineer, or flight navi-gator assigned to duty in an airplane during flighttime.

Flight LevelA level of constant atmospheric pressure related toa reference datum of 29.92 inches of mercury. Eachis stated in three digits that represent hundreds offeet. For example, Flight Level 250 represents abarometric altimeter indication of 25,000 ft; flightlevel 255, an indication of 25,500 ft.

REFERENCE

SECTION 1

viii

Flight Management SystemsA computer system that uses a large database toallow routes to be preprogrammed and fed into thesystem by means of a data loader. The system isconstantly updated with respect to position accu-racy by reference to conventional navigation aids.The sophisticated program and its associated data-base ensures that the most appropriate aids areautomatically selected during the information up-date cycle.

Flight PathThe actual direction and velocity an airplanefollows.

Flight Path AngleThe angle between the flight path vector and thehorizon.

Flight RecorderA general term applied to any instrument or devicethat records information about the performance ofan airplane in flight or about conditions encoun-tered in flight.

Fly-by-Wire AirplanesAirplanes that have electronic flight controlsystems

Instrument Landing SystemA precision instrument approach system that nor-mally consists of the following electronic compo-nents and visual aids:1. Localizer.2. Glideslope.3. Outer marker.4. Middle marker.5. Approach lights.

Instrument Landing System Categories1. ILS Category I – An ILS approach procedure

that provides for approach to a height abovetouchdown of not less than 200 ft and withrunway visual range of not less than 1800 ft.

2. ILS Category II – An ILS approach procedurethat provides for approach to a height abovetouchdown of not less than 100 ft and withrunway visual range of not less than 1200 ft.

3. ILS Category III –IIIA. An ILS approach procedure that provides

for approach without a decision heightminimum and with runway visual rangeof not less than 700 ft.

IIIB. An ILS approach procedure that providesfor approach without a decision heightminimum and with runway visual rangeof not less than 150 ft.

IIIC. An ILS approach procedure that providesfor approach without a decision heightminimum and without runway visualrange minimum.

Instrument Meteorological ConditionsMeteorological conditions expressed in terms ofvisibility, distance from cloud, and ceiling lessthan the minimums specified for visual meteoro-logical conditions.

International Civil Aviation OrganizationA specialized agency of the United Nations whoseobjectives are to develop the principles and tech-niques of international air navigation and fosterplanning and development of international civil airtransport.

Load FactorA measure of the acceleration being experiencedby the airplane.

ManeuverA controlled variation of the flight path.

Mean Sea Level (MSL) AltitudeAltitude expressed in feet measured from mean sealevel.

Mountain WaveSevere turbulence advancing up one side of amountain and down the other.

REFERENCE

ix

Newton’s First LawAn object at rest will tend to stay at rest, and anobject in motion will tend to stay in motion in astraight line, unless acted on by an external force.

Newton’s Second LawAn object in motion will continue in a straight lineunless acted on by an external force.

Force = mass x acceleration

OperatorsThe people who are involved in all operationsfunctions required for the flight of commercialairplanes.

PitchMovement about the lateral axis.

Pitch AttitudeThe angle between the longitudinal axis of theairplane and the horizon.

RollMotion about the longitudinal axis.

Sideslip AngleThe angle between the longitudinal axis of theairplane and the relative wind as seen in a planview.

StabilityPositive static stability is the initial tendency toreturn to an undisturbed state after a disturbance.

StallAn airplane is stalled when the angle of attackis beyond the stalling angle. A stall is character-ized by any of, or a combination of, thefollowing:a. Buffeting, which could be heavy at times.b. A lack of pitch authority.c. A lack of roll control.d. Inability to arrest descent rate.

TrimThat condition in which the forces on the airplaneare stabilized and the moments about the center ofgravity all add up to zero.

TurbulenceTurbulent atmosphere is characterized by a largevariation in an air current over a short distance.

Visual Meteorological ConditionsMeteorological conditions expressed in terms ofvisibility, distance from cloud, and ceiling equal toor better than specified minimums.

VMCAThe minimum flight speed at which the airplane iscontrollable with a maximum of 5-deg bank whenthe critical engine suddenly becomes inoperativewith the remaining engine at takeoff thrust.

Wake TurbulenceThe condition in which a pair of counter-rotatingvortices is shed from an airplane wing, thus causingturbulence in the airplane’s wake.

WindshearWind variations at low altitude

YawMotion about the vertical axis

REFERENCE

Airplane Upset Information

And

Aerodynamics Review

SECTION 2

2.i

2Pilot Guide to Airplane Upset Recovery

Table of Contents

Section Page

2.0 Introduction ....................................................................................................................... 2.1

2.1 Objectives .......................................................................................................................... 2.1

2.2 Definition of Airplane Upset ............................................................................................. 2.1

2.3 The Situation ..................................................................................................................... 2.2

2.4 Causes of Airplane Upsets ................................................................................................ 2.22.4.1 Environmentally Induced Airplane Upsets ....................................................................... 2.32.4.1.1 Turbulence ......................................................................................................................... 2.32.4.1.1.1 Clear Air Turbulence ......................................................................................................... 2.42.4.1.1.2 Mountain Wave .................................................................................................................. 2.42.4.1.1.3 Windshear .......................................................................................................................... 2.42.4.1.1.4 Thunderstorms ................................................................................................................... 2.42.4.1.1.5 Microbursts ........................................................................................................................ 2.62.4.1.2 Wake Turbulence .............................................................................................................. 2.62.4.1.3 Airplane Icing .................................................................................................................... 2.82.4.2 Systems-Anomalies-Induced Airplane Upsets ................................................................. 2.82.4.2.1 Flight Instruments.............................................................................................................. 2.92.4.2.2 Autoflight Systems ............................................................................................................ 2.92.4.2.3 Flight Control and Other Anomalies ................................................................................. 2.92.4.3 Pilot-Induced Airplane Upsets .......................................................................................... 2.92.4.3.1 Instrument Cross-Check ..................................................................................................2.102.4.3.2 Adjusting Attitude and Power ......................................................................................... 2.102.4.3.3 Inattention ........................................................................................................................ 2.102.4.3.4 Distraction From Primary Cockpit Duties ...................................................................... 2.102.4.3.5 Vertigo or Spatial Disorientation .................................................................................... 2.102.4.3.6 Pilot Incapacitation .......................................................................................................... 2.112.4.3.7 Improper Use of Airplane Automation ........................................................................... 2.112.4.4 Combination of Causes ................................................................................................... 2.11

2.5 Swept-Wing Airplane Fundamentals for Pilots .............................................................. 2.122.5.1 Flight Dynamics .............................................................................................................. 2.122.5.2 Energy States ................................................................................................................... 2.122.5.3 Load Factors .................................................................................................................... 2.132.5.4 Aerodynamic Flight Envelope ........................................................................................ 2.162.5.5 Aerodynamics .................................................................................................................. 2.172.5.5.1 Angle of Attack and Stall ................................................................................................ 2.172.5.5.2 Camber............................................................................................................................. 2.202.5.5.3 Control Surface Fundamentals ........................................................................................ 2.212.5.5.3.1 Spoiler-Type Devices....................................................................................................... 2.212.5.5.3.2 Trim .................................................................................................................................. 2.222.5.5.4 Lateral and Directional Aerodynamic Considerations ................................................... 2.232.5.5.4.1 Angle of Sideslip .............................................................................................................. 2.232.5.5.4.2 Wing Dihedral Effects ..................................................................................................... 2.24

SECTION 1SECTION 2

2.ii

2.5.5.4.3 Pilot-Commanded Sideslip ..............................................................................................2.252.5.5.5 High-Speed, High-Altitude Characteristics .................................................................... 2.252.5.5.6 Stability ............................................................................................................................ 2.262.5.5.7 Maneuvering in Pitch ...................................................................................................... 2.272.5.5.8 Mechanics of Turning Flight ........................................................................................... 2.292.5.5.9 Lateral Maneuvering ....................................................................................................... 2.312.5.5.10 Directional Maneuvering................................................................................................. 2.322.5.5.11 Flight at Extremely Low Airspeeds ................................................................................ 2.332.5.5.12 Flight at Extremely High Speeds .................................................................................... 2.33

2.6 Recovery From Airplane Upsets ..................................................................................... 2.342.6.1 Situation Awareness of an Airplane Upset ..................................................................... 2.342.6.2 Miscellaneous Issues Associated With Upset Recovery ................................................ 2.342.6.2.1 Startle Factor ................................................................................................................... 2.342.6.2.2 Negative G Force............................................................................................................. 2.352.6.2.3 Use of Full Control Inputs ............................................................................................... 2.352.6.2.4 Counter-Intuitive Factors ................................................................................................ 2.352.6.2.5 Previous Training in Nonsimilar Airplanes .................................................................... 2.352.6.2.6 Potential Effects on Engines ........................................................................................... 2.352.6.3 Airplane Upset Recovery Techniques............................................................................. 2.352.6.3.1 Stall .................................................................................................................................. 2.362.6.3.2 Nose-High, Wings-Level Recovery Techniques ............................................................ 2.362.6.3.3 Nose-Low, Wings-Level Recovery Techniques ............................................................. 2.372.6.3.4 High-Bank-Angle Recovery Techniques ........................................................................ 2.382.6.3.5 Consolidated Summary of Airplane Recovery Techniques............................................ 2.38

Section Page

SECTION 2

2.1

2Pilot Guide to Airplane Upset Recovery

2.0 Introduction

The “Pilot Guide to Airplane Upset Recovery” isone part of the Airplane Upset Recovery TrainingAid. The other parts include an “Overview forManagement” (Sec. 1), “Example Airplane UpsetRecovery Training Program” (Sec. 3), “Refer-ences for Additional Information” (Sec. 4), and atwo-part video.

The goal of this training aid is to increase theability of pilots to recognize and avoid situationsthat can lead to airplane upsets and to improve theirability to recover control of an airplane that hasexceeded the normal flight regime. This will beaccomplished by increasing awareness of poten-tial upset situations and knowledge of aerodynam-ics and by application of this knowledge duringsimulator training scenarios.

The education material and the recommendationsprovided in the Airplane Upset Recovery TrainingAid were developed through an extensive reviewprocess to achieve a consensus of the air transportindustry.

2.1 ObjectivesThe objectives of the “Pilot Guide to AirplaneUpset Recovery” are to provide pilots with• Knowledge to recognize situations that may

lead to airplane upsets so that they may beprevented.

• Basic airplane aerodynamic information.• Airplane flight maneuvering information and

techniques for recovering airplanes that havebeen upset.

It is intended that this information be provided topilots during academic training and that it beretained for future use.

2.2 Definition of Airplane Upset

Research and discussions within the commercialaviation industry indicated that it was necessary toestablish a descriptive term and definition in orderto develop this training aid. Terms such as “un-usual attitude,” “advanced maneuver,” “selectedevent,” “loss of control,” “airplane upset,” andothers are terms used within the industry. The teamdecided that “airplane upset” was appropriate forthis training aid. An airplane upset is defined as anairplane in flight unintentionally exceeding theparameters normally experienced in line opera-tions or training.

While specific values may vary among airplanemodels, the following unintentional conditionsgenerally describe an airplane upset:• Pitch attitude greater than 25 deg, nose up.• Pitch attitude greater than 10 deg, nose down.• Bank angle greater than 45 deg.• Within the above parameters, but flying at air-

speeds inappropriate for the conditions.

SECTION 2

2.2

2.3 The Situation

The commercial aviation industry has not specifi-cally tracked airplane upset incidents that meetthis training aid’s precise definition; therefore,safety data do not directly correlate to the upsetparameters established for this training aid. How-ever, the data that are available suggest that loss ofcontrol is a problem that deserves attention. Figure 1shows that loss of control in flight accounted formany fatalities during the indicated time period.

2.4 Causes of Airplane Upsets

Airplane upsets are not a common occurrence.This may be for a variety of reasons. Airplanedesign and certification methods have improved.Equipment has become more reliable. Perhapstraining programs have been effective in teachingpilots to avoid situations that lead to airplaneupsets. While airplane upsets seldom take place,there are a variety of reasons why they happen.Figure 2 shows incidents and causes from NASAAviation Safety Reporting System (ASRS) re-ports. The National Transportation Safety Boardanalysis of 20 transport-category loss-of-controlaccidents from 1986 to 1996 indicates that themajority were caused by the airplane stalling(Fig. 3). This section provides a review of the mostprevalent causes for airplane upsets.

0

500

1000

1500

2000

2500

3000

Number offatal accidents

(137 total)

2396

2221

760

CFIT Loss ofcontrolin flight

In-flightfire

Sabotage Mid-air

collision

Hijack Ice/snow

Landing Wind-shear

Fuelexhaus-

tion

Other Runwayincursion

RTO

607506

306162 143 119 113 111

45 3

36 37 4 5 2 8 5 11 3 7 14 4 1

73 = 53%

Total fatalities: 7492

CFIT and loss of control in flight fatalities:4617, or 62%

Number offatalities

Figure 1Worldwide Airline

Fatalities Classifiedby Type of Event,

1987 to 1996

SECTION 2

2.3

2.4.1 Environmentally InducedAirplane Upsets

The predominant number of airplane upsets arecaused by various environmental factors (Fig. 2).Unfortunately, the aviation industry has the leastamount of influence over the environment whencompared to human factors or airplane-anomaly-caused upsets. The industry recognizes this di-lemma and resorts to training as a means foravoiding environmental hazards. Separate educa-tion and training aids have been produced throughan industry team process that addresses turbu-lence, windshear, and wake turbulence.

2.4.1.1 Turbulence

Turbulent atmosphere is characterized by a largevariation in an air current over a short distance.The main causes of turbulence are jet streams,convective currents, obstructions to wind flow,and windshear. Turbulence is categorized as “light,”“moderate,” “severe,” and “extreme.” Refer to anindustry-produced Turbulence Education andTraining Aid for more information about turbu-lence. This aid is available from the NationalTechnical Information Service or The BoeingCompany. Only limited information is presentedin this section for a short review of the subject.

Figure 2MultiengineTurbojet Loss-of-Control Factors,January 1987 toMay 1995, ASRS*

0

10

20

30

40

50

60

70

80

90

100

Total number ofincidents: 297

MicroburstYawdamper

AileronsRudderWindshearFlapsAutopilotAircrafticing

SevereWx

turbulence

Aircraftwake

turbulence

Numberofincidents

*The ASRS database is current through May 1995.Data are based on ASRS reports containing any reference to loss of control involving the above factors that include reporter narratives.

0

2

4

6

8

Stall Flight controls/systems/structure

Icing Microburst

Causes of loss-of-control accidents, 1986 to 1996

Numberof accidents

Crewdisorientation

Other/unknown

Figure 3Loss-of-ControlAccidents (Trans-port Category)

SECTION 2

2.4

Knowledge of the various types of turbulenceassists in avoiding it and, therefore, the potentialfor an airplane upset.

In one extreme incident, an airplane encounteredsevere turbulence that caused the number 2 engineto depart the airplane. The airplane entered a roll50 deg left, followed by a huge yaw. Several pitchand roll oscillations were reported. The crew re-covered and landed the airplane.

2.4.1.1.1 Clear Air Turbulence

Clear air turbulence (CAT) is defined by the Aero-nautical Information Manual as “high-level turbu-lence (normally above 15,000 ft above sea level)not associated with cumuliform cloudiness, in-cluding thunderstorms.”

Although CAT can be encountered in any layer ofthe atmosphere, it is almost always present in thevicinity of jet streams. A number of jet streams(high-altitude paths of winds exceeding velocitiesof 75 to 100 kn) may exist at any given time, andtheir locations will vary constantly. CAT becomesparticularly difficult to predict as it is extremelydynamic and does not have common dimensionsof area or time. In general, areas of turbulenceassociated with a jet stream are from 100 to 300 milong, elongated in the direction of the wind; 50 to100 mi wide; and 2000 to 5000 ft deep. These areasmay persist from 30 min to 1 day. CAT near the jetstream is the result of the difference in wind-speeds and the windshear generated between points.CAT is considered moderate when the verticalwindshear is 5 kn per 1000 ft or greater and thehorizontal shear is 20 kn per 150 nm, or both.Severe CAT occurs when the vertical shear is 6 knper 1000 ft and the horizontal shear is 40 kn per150 nm or greater, or both.

2.4.1.1.2 Mountain Wave

Mountains are the greatest obstructions to windflow. This type of turbulence is classified as “me-chanical” because it is caused by a mechanicaldisruption of wind. Over mountains, rotor or len-ticular clouds are sure signs of turbulence. How-ever, mechanical turbulence may also be present inair too dry to produce clouds. Light to extremeturbulence is created by mountains.

Severe turbulence is defined as that which causeslarge, abrupt changes in altitude or attitude. Itusually causes large variation in indicated air-

speed. The airplane may be momentarily out ofcontrol. Severe turbulence can be expected inmountainous areas where wind components ex-ceeding 50 kn are perpendicular to and near theridge level; in and near developing and maturethunderstorms; occasionally, in other toweringcumuliform clouds; within 50 to 100 mi on the coldside of the center of the jet stream; in troughs aloft;and in lows aloft where vertical windshears exceed10 kn per 1000 ft and horizontal windshears ex-ceed 40 kn per 150 mi.

Extreme turbulence is defined as that in which theairplane is violently tossed around and practicallyimpossible to control. It may cause structural dam-age. Extreme turbulence can be found in moun-tain-wave situations, in and below the level ofwell-developed rotor clouds, and in severethunderstorms.

2.4.1.1.3 Windshear

Wind variations at low altitude have long beenrecognized as a serious hazard to airplanes duringtakeoff and approach. These wind variations canresult from a large variety of meteorological con-ditions, such as topographical conditions, tem-perature inversions, sea breezes, frontal systems,strong surface winds, and the most violent forms ofwind change—thunderstorms and rain showers.Thunderstorms and rain showers may produce anairplane upset, and they will be discussed in thefollowing section. The Windshear Training Aidprovides comprehensive information onwindshear avoidance and training. This aid isavailable from the National Technical InformationService or The Boeing Company.

2.4.1.1.4 Thunderstorms

There are two basic types of thunderstorms: airmassand frontal. Airmass thunderstorms appear to berandomly distributed in unstable air, and theydevelop from localized heating at the Earth’s sur-face (Fig. 4). The heated air rises and cools to formcumulus clouds. As the cumulus stage continues todevelop, precipitation forms in high portions of thecloud and falls. Precipitation signals the beginningof the mature stage and the presence of a downdraft.After approximately an hour, the heated updraftcreating the thunderstorm is cut off by rainfall.Heat is removed and the thunderstorm dissipates.Many thunderstorms produce an associated cold-air gust front as a result of the downflow andoutrush of rain-cooled air. These gust fronts are

SECTION 2

2.5

usually very turbulent, and they can create a seri-ous airplane upset, especially during takeoff andapproach.

Frontal thunderstorms are usually associated withweather systems line fronts, converging wind, andtroughs aloft (Fig. 5). Frontal thunderstorms formin squall lines; last several hours; generate heavyrain, and possibly hail; and produce strong gustywinds, and possibly tornadoes. The principal dis-tinction in formation of these more severe thunder-storms is the presence of large, horizontal wind

changes (speed and direction) at different altitudesin the thunderstorm. This causes the severe thun-derstorm to be vertically tilted. Precipitation fallsaway from the heated updraft, permitting a muchlonger storm development period. Resulting air-flows within the storm accelerate to much highervertical velocities, which ultimately results inhigher horizontal wind velocities at the surface.The downward moving column of air, or downdraft,of a typical thunderstorm is fairly large, about 1 to5 mi in diameter. Resultant outflows may producelarge changes in windspeed.

Figure 4Airmass Thunder-storm Life Cycle

Figure 5Severe FrontalThunderstormAnatomy

Light rain

Cumulus stage

Localized surfaceheating

= Airflow/circulation Surface cooling

Mature stageDissipating stage

Rain

Gustfront

Surface heating

Heavy rainand hail

Wind

Airflowcirculation

DowndraftDowndraft

Updraft

Anvil

SECTION 2

2.6

when exiting the microburst. Windspeeds inten-sify for about 5 min after a microburst initiallycontacts the ground and typically dissipate within10 to 20 min after ground contact.

It is vital to recognize that some microburstscannot be successfully escaped with any knowntechniques.

2.4.1.2 Wake Turbulence

Wake turbulence is the leading cause of airplaneupsets that are induced by the environment. Thephenomenon that creates wake turbulence resultsfrom the forces that lift the airplane. High-pressureair from the lower surface of the wings flowsaround the wingtips to the lower pressure regionabove the wings. A pair of counter-rotating vorti-

2.4.1.1.5 Microbursts

Identification of concentrated, more powerfuldowndrafts—known as microbursts—has resultedfrom the investigation of windshear accidents andfrom meteorological research. Microbursts canoccur anywhere convective weather conditionsoccur. Observations suggest that approximately5% of all thunderstorms produce a microburst.Downdrafts associated with microbursts are typi-cally only a few hundred to 3000 ft across. Whena downdraft reaches the ground, it spreads outhorizontally and may form one or more horizontalvortex rings around the downdraft (Fig. 6).Microburst outflows are not always symmetric.Therefore, a significant airspeed increase may notoccur upon entering outflows, or it may be muchless than the subsequent airspeed loss experienced

Figure 6Symmetric

Microburst—Anairplane transiting

the microburstwould experienceequal headwinds

and tailwinds.

DowndraftVirga or rain

Horizontalvortex

Outflowfront

Outflow

1000 ftApproximatescale

1000 ft0

Cloud Base

SECTION 2

2.7

ces are thus shed from the wings: the right wingvortex rotates counterclockwise, and the left wingvortex rotates clockwise (Fig. 7). The region ofrotating air behind the airplane is where waketurbulence occurs. The strength of the turbulenceis determined predominantly by the weight, wing-span, and speed of the airplane. Generally, vorticesdescend at an initial rate of about 300 to 500 ft/minfor about 30 sec. The descent rate decreases andeventually approaches zero at between 500 and900 ft below the flight path. Flying at or above theflight path provides the best method for avoidance.Maintaining a vertical separation of at least 1000 ftwhen crossing below the preceding aircraft may beconsidered safe. This vertical motion is illustratedin Figure 8. Refer to the Wake Turbulence Train-ing Aid for comprehensive information on how toavoid wake turbulence. This aid is available from

the National Technical Information Service or TheBoeing Company.

An encounter with wake turbulence usually resultsin induced rolling or pitch moments; however, inrare instances an encounter could cause structuraldamage to the airplane. In more than one instance,pilots have described an encounter to be like “hit-ting a wall.” The dynamic forces of the vortex canexceed the roll or pitch capability of the airplane toovercome these forces. During test programs, thewake was approached from all directions to evalu-ate the effect of encounter direction on response.One item was common to all encounters: withouta concerted effort by the pilot to reenter the wake,the airplane would be expelled from the wake andan airplane upset could occur.

500 to 900 ft

Flight path

Levels off in approximately 5 nm in approach configuration

Figure 7Wake TurbulenceFormation

Figure 8Vertical MotionOut of GroundEffect

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2.8

Counter-control is usually effective and inducedroll is minimal in cases where the wingspan andailerons of the encountering airplane extend be-yond the rotational flowfield of the vortex (Fig. 9).It is more difficult for airplanes with short wing-span (relative to the generating airplane) to counterthe imposed roll induced by the vortex flow.

Avoiding wake turbulence is the key to avoidingmany airplane upsets. Pilot and air traffic controlprocedures and standards are designed to accom-plish this goal, but as the aviation industry ex-pands, the probability of an encounter alsoincreases.

2.4.1.3 Airplane Icing

Technical literature is rich with data showing theadverse aerodynamic effects of airfoil contamina-tion. Large degradation of airplane performancecan result from the surface roughness of an ex-tremely small amount of contamination. Thesedetrimental effects vary with the location androughness, and they produce unexpected airplanehandling characteristics, including degradation ofmaximum lift capability, increased drag, and pos-sibly unanticipated changes in stability and con-trol. Therefore, the axiom of “Keep it clean” forcritical airplane surfaces continues to be a univer-sal requirement.

2.4.2 Systems-Anomalies-InducedAirplane Upsets

Airplane designs, equipment reliability, and flightcrew training have all improved since the Wrightbrothers’ first powered flight. Airplane certifica-tion processes and oversight are rigorous. Airlinesand manufacturers closely monitor equipment fail-ure rates for possible redesign of airplane parts ormodification of maintenance procedures. Dissemi-nation of information is rapid if problems aredetected. Improvement in airplane designs andequipment components has always been a majorfocus in the aviation industry. In spite of thiscontinuing effort, there are still failures. Some ofthese failures can lead to an airplane upset. That iswhy flight crews are trained to overcome or miti-gate the impact of the failures. Most failures aresurvivable if correct responses are made by theflight crew.

An airplane was approaching an airfield and ap-peared to break off to the right for a left downwindto the opposite runway. On downwind at approxi-mately 1500 ft, the airplane pitched up to nearly 60deg and climbed to an altitude of nearly 4500 ft,with the airspeed deteriorating to almost 0 kn. Theairplane then tail-slid, pitched down, and seem-ingly recovered. However, it continued into an-other steep pitchup of 70 deg. This time as it

Wake vortexflow

field

Counter-control

Figure 9Induced Roll

SECTION 2

2.9

tail-slid, it fell off toward the right wing. As itpitched down and descended again, seeminglyrecovering, the airplane impacted the ground in aflat pitch, slightly right wing down. The digitalflight data recorder indicated that the stabilizertrim was more than 13 units nose up. The flightcrew had discussed a trim problem during thedescent but made no move to cut out the electrictrim or to manually trim. The accident was surviv-able if the pilot had responded properly.

2.4.2.1 Flight Instruments

The importance of reliable flight instruments hasbeen known from the time that pilots first began torely on artificial horizons. This resulted in con-tinual improvements in reliability, design, redun-dancy, and information provided to the pilots.

However, instrument failures do infrequentlyoccur. All airplane operations manuals provideflight instrument system information so that whenfailures do happen, the pilot can analyze the impactand select the correct procedural alternatives. Air-planes are designed to make sure pilots have atleast the minimum information needed to safelycontrol the airplane.

In spite of this, several accidents point out thatpilots are not always prepared to correctly analyzethe alternatives, and an upset takes place. Duringthe takeoff roll, a check of the airspeed at 80 knrevealed that the Captain’s airspeed was not func-tioning. The takeoff was continued. When theairplane reached 4700 ft, about 2 min into theflight, some advisory messages appeared inform-ing the crew of flight control irregularities. Com-ments followed between the pilots about confusionthat was occurring between the airspeed indicationsystems from the left-side airspeed indication sys-tem, affecting the indication of the left-side air-speed autopilot and activation of the overspeedwarning. The airplane continued flying with theautopilot connected and receiving an erroneousindication in the Captain’s airspeed. Recordedsounds and flight data indicated extreme condi-tions of flight, one corresponding to overspeed andthe other to slow speed (stick shaker). The Captaininitiated an action to correct the overspeed, and thecopilot advised that his airspeed indicator wasdecreasing. The airplane had three airspeed indi-cating systems, and at no time did the flight crewmention a comparison among the three systems.The flight recorders indicated the airplane was out

of control for almost 2 min until impact. Expertsdetermined that the anomalies corresponded toconditions equal to an obstruction in the Captain’sairspeed sensors (pitot head).

2.4.2.2 Autoflight Systems

Autoflight systems include the autopilot,autothrottles, and all related systems that performflight management and guidance. The systemsintegrate information from a variety of other air-plane systems. They keep track of altitude, head-ing, airspeed, and flight path with unflaggingaccuracy. The pilot community has tended to de-velop a great deal of confidence in the systems, andthat has led to complacency in some cases. Asreliable as the autoflight systems may be, they can,and have, malfunctioned. Because of the integra-tion of systems, it may even be difficult for thepilot to analyze the cause of the anomaly, andairplane upsets have occurred. Since advancedautomation may tend to mask the cause of theanomaly, an important action in taking control ofthe airplane is to reduce the level of automation.Disengaging the autopilot, the autothrottles, orboth, may help in analyzing the cause of theanomaly by putting the pilot in closer touch withthe airplane and perhaps the anomaly.

2.4.2.3 Flight Control and Other Anomalies

Flight control anomalies, such as flap asymmetry,spoiler problems, and others, are addressed inairplane operations manuals. While they are rareevents, airplane certification requirements ensurethat pilots have sufficient information and aretrained to handle these events. However, pilotsshould be prepared for the unexpected, especiallyduring takeoffs. Engine failure at low altitudeswhile the airplane is at a low-energy condition isstill a demanding maneuver for the pilot to handle.An erroneous stall warning on takeoff or shortlyafter takeoff could be a situation that allows theairplane to become upset.

2.4.3 Pilot-Induced Airplane UpsetsWe have known for many years that sensory inputscan be misleading to pilots, especially when theycannot see the horizon. To solve this problem,airplanes are equipped with flight instruments toprovide the necessary information for controllingthe airplane.

SECTION 2

2.10

2.4.3.1 Instrument Cross-Check

Pilots must cross-check and interpret the instru-ments and apply the proper pitch, bank, and poweradjustments. Misinterpretation of the instrumentsor slow cross-checks by the pilot can lead to anairplane upset.

An important factor influencing cross-check tech-nique is the ability of the pilot: “All pilots do notinterpret instrument presentations with the samespeed; some are faster than others in understand-ing and evaluating what they see. One reason forthis is that the natural ability of pilots varies.Another reason is that the experience levels aredifferent. Pilots who are experienced and fly regu-larly will probably interpret their instruments morequickly than inexperienced pilots.”1

2.4.3.2 Adjusting Attitude and Power

A satisfactory instrument cross-check is only onepart of the equation. It is necessary for the pilot tomake the correct adjustments to pitch, bank, andpower in order to control the airplane. Airplaneupsets have occurred when the pilot has madeincorrect adjustments. This can happen when thepilot is not familiar with the airplane responses topower adjustments or control inputs. There havealso been instances when two pilots have appliedopposing inputs simultaneously.

2.4.3.3 Inattention

A review of airplane upsets shows that inattentionor neglecting to monitor the airplane performancecan result in minor excursions from normal flightregimes to extreme deviations from the norm.Many of the minor upsets can be traced to animproper instrument cross-check; for example,neglecting to monitor all the instruments or fixat-ing on certain instrument indications and not de-tecting changes in others. Some instrumentindications are not as noticeable as others. Forexample, a slight heading change is not as eye-catching as a 1000-ft/min change in vertical veloc-ity indication.

There are many extreme cases of inattention by theflight crew that have resulted in airplane upsetaccidents. In one accident, a crew had discussed arecurring autothrottle problem but continued touse the autothrottle. On level-off from a descent,

one throttle remained at idle and the other compen-sated by going to a high power setting. The result-ing asymmetric thrust exceeded the autopilotauthority and the airplane began to roll. At ap-proximately 50 deg of bank, full pro-roll lateralcontrol wheel was applied. The airplane rolled 168deg into a steep dive of 78 deg, nose low, andcrashed.

2.4.3.4 Distraction From PrimaryCockpit Duties

“Control the airplane first” has always been aguiding principle in flying. Unfortunately, it is notalways followed. In this incident, both pilots werefully qualified as pilot-in-command and were su-pervising personnel. The Captain left the left seat,and the copilot set the airplane on autopilot andwent to work on a clipboard on his lap. At this pointthe autopilot disengaged, possibly with no annun-ciator light warning. The airplane entered a steep,nose-down, right spiral. The copilot’s instrumentpanel went blank, and he attempted to use thepilot’s artificial horizon. However, it had tumbled.In the meantime, the Captain returned to his stationand recovered the airplane at 6000 ft using needleand ball. This is just one of many incidents wherepilots have become distracted. Many times, thedistraction is caused by relatively minor reasons,such as caution lights or engine performanceanomalies.

2.4.3.5 Vertigo or Spatial Disorientation

Spatial disorientation has been a significant factorin many airplane upset accidents. The definition ofspatial disorientation is the inability to correctlyorient oneself with respect to the Earth’s surface.A flight crew was climbing to about 2000 ft atnight during a missed approach from a secondInstrument Landing System (ILS) approach. Theweather was instrument meteorological conditions(IMC)– ceiling: 400 ft, visibility: 2 mi, rain, andfog. The airplane entered a spiral to the left. TheCaptain turned the controls over to the First Of-ficer, who was unsuccessful in the recovery at-tempt. The airplane hit trees and was destroyed byground impact and fire. [NTSB/AAR-92-05]

All pilots are susceptible to sensory illusions whileflying at night or in certain weather conditions.These illusions can lead to a conflict betweenactual attitude indications and what the pilot “feels”

1. Source: Instrument Flight Procedures. Air Force Manual 11-217, Vol. 1 (1 April 1996).

SECTION 2

2.11

is the correct attitude. Disoriented pilots may notalways be aware of their orientation error. Manyairplane upsets occur while the pilot is busilyengaged in some task that takes attention awayfrom the flight instruments. Others perceive aconflict between bodily senses and the flight in-struments but allow the airplane to become upsetbecause they cannot resolve the conflict. Unrecog-nized spatial disorientation tends to occur duringtask-intensive portions of the flight, while recog-nized spatial disorientation occurs during attitude-changing maneuvers.

There are several situations that may lead to visualillusions and then airplane upsets. A pilot canexperience false vertical and horizontal cues. Fly-ing over sloping cloud decks or land that slopesgradually upward into mountainous terrain oftencompels pilots to fly with their wings parallel to theslope, rather than straight and level. A relatedphenomenon is the disorientation caused by theAurora Borealis in which false vertical and hori-zontal cues generated by the aurora result in atti-tude confusion.

It is beyond the scope of this training aid to expandon the physiological causes of spatial disorienta-tion, other than to alert pilots that it can result inloss of control of an airplane. It should be empha-sized that the key to success in instrument flying isan efficient instrument cross-check. The only reli-able aircraft attitude information, at night or inIMC, is provided by the flight instruments. Anysituation or factor that interferes with this flow ofinformation, directly or indirectly, increases thepotential for disorientation. The pilot’s role inpreventing airplane upsets due to spatial disorien-tation essentially involves three things: training,good flight planning, and knowledge of proce-dures. Both pilots must be aware that it can happen,and they must be prepared to control the airplaneif the other person is disoriented.

2.4.3.6 Pilot Incapacitation

A First Officer fainted while at the controls enroute to the Azores, Portugal. He slumped againstthe controls, and while the rest of the flight crewwas removing him from his flight position, theairplane pitched up and rolled to over 80 deg ofbank. The airplane was then recovered by theCaptain. While this is a very rare occurrence, itdoes happen, and pilots need to be prepared toreact properly. Another rare possibility for air-

plane upset is an attempted hijack situation. Pilotsmay have very little control in this critical situa-tion, but they must be prepared to recover theairplane if it enters into an upset.

2.4.3.7 Improper Use of Airplane Automation

The following incident describes a classic case ofimproper use of airplane automation. “During anapproach with autopilot 1 in command mode, amissed approach was initiated at 1500 ft. It isundetermined whether this was initiated by thepilots; however, the pilot attempted to counteractthe autopilot-commanded pitchup by pushing for-ward on the control column. Normally, pushing onthe control column would disengage the autopilot,but automatic disconnect was inhibited in go-around mode in this model airplane. As a result ofthe control column inputs, the autopilot trimmedthe stabilizer to 12 deg, nose up, in order tomaintain the programmed go-around profile. Mean-while, the pilot-applied control column forcescaused the elevator to deflect 14 deg, nose down.The inappropriate pilot-applied control columnforces resulted in three extreme pitchup stallsbefore control could be regained. The airplanesystems operated in accordance with design speci-fications.” [FSF, Flight Safety Digest 1/92]

The advancement of technology in today’s mod-ern airplanes has brought us flight directors, auto-pilots, autothrottles, and flight managementsystems. All of these devices are designed toreduce the flight crew workload. When used prop-erly, this technology has made significant contri-butions to flight safety. But technology can includecomplexity and lead to trust and eventual compla-cency. The systems can sometimes do things thatthe flight crew did not intend for them to do.Industry experts and regulators continue to worktogether to find the optimal blend of hardware,software, and pilot training to ensure the highestpossible level of system performance—which cen-ters on the human element.

2.4.4 Combination of CausesA single cause of an airplane upset can be theinitiator of other causes. In one instance, a possibleinadvertent movement of the flap/slat handle re-sulted in the extension of the leading edge slats.The Captain’s initial reaction to counter the pitchupwas to exert forward control column force; thecontrol force when the autopilot disconnected re-

SECTION 2

2.12

sulted in an abrupt airplane nose-down elevatorcommand. Subsequent commanded elevator move-ments to correct the pitch attitude induced severalviolent pitch oscillations. The Captain’s com-manded elevator movements were greater thannecessary because of the airplane’s light controlforce characteristics. The oscillations resulted in aloss of 5000 ft of altitude. The maximum nose-down pitch attitude was greater than 20 deg, andthe maximum normal accelerations were greaterthan 2 g and less than 1 g.

This incident lends credence to the principle usedthroughout this training aid: Reduce the level ofautomation while initiating recovery; that is, dis-connect the autopilot and autothrottle, and do notlet the recovery from one upset lead to another.

2.5 Swept-Wing Airplane Fundamentalsfor Pilots

2.5.1 Flight Dynamics

In understanding the flight dynamics of large,swept-wing transport airplanes, it is important tofirst understand what causes the forces and mo-ments acting on the airplane and then move to whatkinds of motion these forces cause. Finally, withthis background, one can gain an understanding ofhow a pilot can control these forces and momentsin order to direct the flight path.

Newton’s first law states that an object at rest willtend to stay at rest, and an object in motion willtend to stay in motion in a straight line, unless actedon by an external force. This definition is funda-mental to all motion, and it provides the founda-tion for all discussions of flight mechanics. Acareful examination of this law reveals an impor-tant subtlety, which is the reference to motion in astraight line. If an airplane in motion is to deviatefrom a straight line, there must be a force, or acombination of forces, imposed to achieve thedesired trajectory. The generation of the forces isthe subject of aerodynamics (to be discussed later).The generation of forces requires energy.

2.5.2 Energy StatesA pilot has three sources of energy available tomanage or manipulate to generate aerodynamicforces and thus control the flight path of anairplane.

The term “energy state” describes how much ofeach kind of energy the airplane has available atany given time. Pilots who understand the airplaneenergy state will be in a position to know instantlywhat options they may have to maneuver theirairplane. The three sources of energy available tothe pilot are• Kinetic energy, which increases with increas-

ing airspeed.• Potential energy, which is proportional to

altitude.• Chemical energy, from the fuel in the tanks.

The airplane is continuously expending energy; inflight, this is because of drag. (On the ground,wheel brakes and thrust reversers, as well as fric-tion, dissipate energy.) This drag energy in flight isusually offset by using some of the stored chemicalenergy—by burning fuel in the engines.

During maneuvering, these three types of energycan be traded, or exchanged, usually at the cost ofadditional drag. This process of consciously ma-nipulating the energy state of the airplane is re-ferred to as “energy management.” Airspeed canbe traded for altitude, as in a zoom-climb. Altitudecan be traded for airspeed, as in a dive. Storedenergy can be traded for either altitude or airspeedby advancing the throttles to command more thrustthan required for level flight. The trading of energymust be accomplished, though, with a view towardthe final desired energy state. For example, whilealtitude can be traded for airspeed by diving theairplane, care must be taken in selecting the angleof the dive so that the final desired energy state willbe captured.

This becomes important when the pilot wants togenerate aerodynamic forces and moments to ma-neuver the airplane. Only kinetic energy (airspeed)can generate aerodynamic forces and maneuvercapability. Kinetic energy can be traded for poten-tial energy (climb). Potential energy can only beconverted to kinetic energy. Chemical energy canbe converted to either potential or kinetic energy,but only at specified rates. These energy relation-ships are shown in Figure 10.

High-performance jet transport airplanes are de-signed to exhibit very low drag in the cruise con-figuration. This means that the penalty for tradingairspeed for altitude is relatively small. Jet trans-port airplanes are also capable of gaining speedvery rapidly in a descent. The pilot needs to exer-cise considerable judgment in making very large

SECTION 2

2.13

energy trades. Just as the level flight accelerationcapability is limited by the maximum thrust of theengines, the deceleration capability is limited bythe ability to generate very large drag increments.For high-performance jet transport airplanes, theability to generate large decelerating drag incre-ments is often limited. The pilot always should beaware of these limitations for the airplane beingflown. A very clean airplane operating near itslimits can easily go from the low-speed boundaryto and through the high-speed boundary veryquickly.

The objective in maneuvering the airplane is tomanage energy so that kinetic energy stays be-tween limits (stall and placards), the potentialenergy stays within limits (terrain to buffet alti-tude), and chemical energy stays above certainthresholds (not running out of fuel). This objectiveis especially important during an inadvertent upsetand the ensuing recovery.

In managing these energy states and trading be-tween the various sources of energy, the pilot doesnot directly control the energy. The pilot controlsthe orientation and magnitude of the various forcesacting on the airplane. These forces result in accel-erations applied to the airplane. The result of theseaccelerations is a change in the orientation of theairplane and a change in the direction or magni-tude, or both, of the flight path vector. Ultimately,velocity and altitude define the energy state.

This process of controlling forces to change accel-erations and produce a new energy state takes time.The amount of time required is a function of themass of the airplane and the magnitude of the

applied forces, and it is also governed by Newton’slaws. Airplanes of larger mass generally take longerto change orientation than do smaller ones. Thelonger time requires the pilot to plan ahead more ina large-mass airplane and make sure that the ac-tions taken will achieve the final desired energystate.

2.5.3 Load FactorsLoad factor in the realm of flight mechanics is ameasure of the acceleration being experienced bythe airplane. By Newton’s second law,

force = mass x acceleration

Since the airplane has mass, if it is being acceler-ated there must be a force acting on it. Conversely,if there is a force acting on an airplane, it willaccelerate. In this case, acceleration refers to achange in either magnitude or direction of thevelocity. This definition of acceleration is muchmore broad than the commonplace reference toacceleration as simply “speeding up.” Accelera-tion has dimensions (length/time2). It is conve-nient to refer to acceleration by comparing it to theacceleration due to gravity (which is 32.2 ft/s2 or9.81 m/s2). Acceleration is expressed in this way asunits of gravity (g).

In addition, the acceleration (or load factor in g’s)is typically discussed in terms of componentsrelative to the principal axes of the airplane:• Longitudinal (fore and aft, typically thought of

as speed change).• Lateral (sideways).• Vertical (or normal).

Figure 10EnergyRelationships

Aerodynamic forces,maneuver capability

Potential energy

Chemical energy

Kinetic energy

SECTION 2

2.14

Frequently, load factor is thought of as being onlyperpendicular to the floor of the airplane. But theforce, and thus the acceleration, may be at anyorientation to the airplane, and the vertical, ornormal, load factor represents only one compo-nent of the total acceleration. In sideslip, for ex-ample, there is a sideways acceleration, and thepilot feels pushed out of the seat sideways. In asteep climb or a rapid acceleration, the pilot feelsforced back into the seat.

In level flight, the vertical load factor is one timesthe acceleration due to gravity, or 1.0 (Fig. 11).This means that the wing is producing lift equal to1.0 times the weight of the airplane, and it isoriented in a direction opposed to the gravityvector. In a pull-up, the load factor is above 1.0(Fig. 12).

In the example in Figure 12, the load factor is 2.0.That is, the force generated by the airplane (wings,fuselage, etc.) is twice that of gravity. Also note

Figure 11Four Forces

of Flight

Figure 12Airplane in

Pull-Up

Drag Thrust

Lift = 1 x weight

Weight

Level flightpath

Weight

Flight pathis curved.

Lift > 1 x weight

SECTION 2

2.15

that the flight path is now curved. Newton’s firstlaw says that an object will continue in a straightline unless acted on by a force. In this case, the liftforce is acting in a perpendicular direction to thevelocity, and the resulting flight path is curved.

In a sustained vertical climb along a straight line,the thrust must be greater than the weight and drag.The load factor perpendicular to the airplane floormust be zero (Fig. 13a).

If it were anything but zero, the flight path wouldnot be a straight line (Fig. 13b).

Note that the acceleration is a result of the sum ofall forces acting on the airplane. One of thoseforces is always gravity. Gravity always producesan acceleration directed toward the center of theEarth. The airplane attitude determines the direc-tion of the gravitational force with respect to theairplane. Aerodynamic forces are produced as aresult of orientation and magnitude of the velocity

Figure 13bAirplane VerticalWith ForcesUnbalanced

Figure 13a(far left) AirplaneVertical With ForcesBalanced

Weight

Drag

Thrust >

Flight pathvertical

weightanddrag

Load factormust bezero

No force in thisdirection

Weight

Drag

Flight pathnot straight

Still noforce in thisdirection

Load factormore thanzero

Thrust

SECTION 2

2.16

vector relative to the airplane, which is reducedinto angles of attack and sideslip. (Refer to Sec.2.5.5, Aerodynamics, for a detailed discussion.) Itis the direction and speed of the airplane throughthe air that results in aerodynamic forces (e.g.,straight ahead or sideways, fast or slow). It is theorientation of the airplane to the center of the Earththat determines the orientation of the gravityvector.

Current jet transport airplanes are certificated towithstand normal vertical load factors from –1.0 to2.5 g in the cruise configuration. Figure 14 is atypical v-n diagram for a transport airplane (“v”for velocity, “n” for number of g’s acceleration). Inaddition to the strength of the structure, the han-dling qualities are demonstrated to be safe withinthese limits of load factor. This means that a pilotshould be able to maneuver safely to and fromthese load factors at these speeds without needingexceptional strength or skill.

Pilots should be aware of the various weight,configuration, altitude, and bank angle specifics ofthe diagrams for the particular airplane they flyand of the limitations imposed by them.

2.5.4 Aerodynamic Flight EnvelopeAirplanes are designed to be operated in well-defined envelopes of airspeed and altitude. Theoperational limits for an airplane—stall speeds,placarded maximum speeds and Mach numbers,and maximum certificated altitudes—are in theApproved Flight Manual (AFM) for each indi-vidual airplane. Within these limits, the airplaneshave been shown to exhibit safe flightcharacteristics.

Manufacturing and regulatory test pilots haveevaluated the characteristics of airplanes in condi-tions that include inadvertent exceedances of theseoperational envelopes to demonstrate that the air-

Figure 14Load Factor

Envelope ShowingSpeeds and Load

Factors

Figure 15Aerodynamic

Flight Envelope

Airspeed

Loadfactor

-1

0

1

2

3

Flaps down

Flaps up

Flaps up

S1 A C D

VS1

VA

VC

VD

= flaps up 1-g stallspeed

= design maneuverspeed, flaps up

= design structuredcruising speed

= design dive speedV V V V

Maximum operating altitude

Stallspeed*

Altitude

Airspeed

MDF

VDFVMO

MMO

MMO

MDF

VMO

V DF

= maximum operatingMach number

= maximum flight-demonstrated Machnumber

= maximum operatingairspeed

= maximum flight-demonstratedairspeed

* Function of airplane configuration and load factor.

SECTION 2

2.17

planes can be returned safely to the operationalenvelopes. Figure 15 depicts a typical flight enve-lope. M

MO and V

MO are the operational limitations,

but the figure also shows the relationship to MDF

and VDF

, the maximum dive speeds demonstratedin flight test. These are typically 0.05 to 0.07 Machand 50 kn higher than the operational limits. In theregion between the operational envelope and thedive envelope, the airplane is required to exhibitsafe characteristics. Although the characteristicsare allowed to be degraded in that region fromthose within the operational flight envelope, theyare shown to be adequate to return the airplane tothe operational envelope if the airplane is outsidethe operational envelope.

2.5.5 AerodynamicsAside from gravity and thrust forces, the otherforces acting on an airplane are generated as aresult of the changing pressures produced on the

surfaces that result in turn from the air flowingover them. A brief review of basic fundamentalaerodynamic principles will set the stage for dis-cussion of airplane upset flight dynamics.

2.5.5.1 Angle of Attack and Stall

Most force-generating surfaces on modern jet trans-port airplanes are carefully tailored to generatelifting forces efficiently. Wings and tail surfacesall produce lift forces in the same way. Figure 16shows a cross section of a lifting surface and thefamiliar definition of angle of attack. The lift forcein pounds generated by a surface is a function ofthe angle of attack, the dynamic pressure (which isproportional to the air density and the square of thetrue airspeed) of the air moving around it, and thesize of the surface.

It is important to understand the dependence of lifton angle of attack. Figure 17 shows how lift varies

Figure 16Airfoil at Angleof Attack

Chord line

Relative wind

Lift is function of

Angle ofattack

• Speed.• Density.• Wing area.• Angle of attack.

Figure 17Lift at Angleof Attack

Angle of attack

Lift

Not stalled StalledMaximumlift

Critical angleof attack

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2.18

with angle of attack for constant speed and airdensity. Important features of this dependencyinclude the fact that at zero angle of attack, lift isnot zero. This is because most lifting surfaces arecambered. Further, as angle of attack is increased,lift increases proportionally, and this increase inlift is normally quite linear. At higher angles ofattack, however, the lift due to angle of attackbehaves differently. Instead of increasing with anincrease in angle of attack, it decreases. At thiscritical angle of attack, the air moving over theupper surface can no longer remain attached to thesurface, the flow breaks down, and the surface isconsidered stalled.

It is necessary to understand that this breakdown ofthe flow and consequent loss of lift is dependentonly on the angle of attack of the surface. Exceedthe critical angle of attack and the surface willstall, and lift will decrease instead of increasing.This is true regardless of airplane speed or atti-tude. In order to sustain a lifting force on theaerodynamic surfaces, the pilot must ensure thatthe surfaces are flown at an angle of attack belowthe stall angle, that is, avoid stalling the airplane.

Depending on the context in which it is used,aerodynamicists use the term “angle of attack” ina number of ways. Angle of attack is always theangle between the oncoming air or relative wind,and some reference line on the airplane or wing.Sometimes it is referenced to the chord line at aparticular location on the wing, sometimes to an“average” chord line on the wing, other times it isreferenced to a convenient reference line on the

airplane, like the body reference x axis. Regardlessof the reference, the concept is the same as are theconsequences: exceed the critical angle of attackand the lifting surfaces and wind will separate,resulting in a loss of lift on those surfaces. Fre-quently the term “Airplane Angle of Attack” isused to refer to the angle between the relative windand the longitudinal axis of the airplane. In flightdynamics, this is frequently reduced to simply“angle of attack.”

Angle of attack can sometimes be confusing be-cause there is not typically an angle-of-attackindicator in most commercial jet transport air-planes. The three angles usually referred to in thelongitudinal axis are• Angle of attack.• Flight path angle.• Pitch angle.These three angles and their relationships to eachother are shown in Figure 18.

Pitch attitude, or angle, is the angle between thelongitudinal axis of the airplane and the horizon.This angle is displayed on the Attitude Indicator orartificial horizon.

The flight path angle is the angle between the flightpath vector and the horizon. This is also the climb(or descent angle). On the newest generation jettransports, this angle can be displayed on thePrimary Flight Display (PFD), as depicted in Fig-ure 18. Flight path angle can also be inferred fromthe Vertical Speed Indicator (VSI) or altimeter, if

Figure 18Pitch Attitude,

Flight Path Angle,and Angle of

Attack

Horizon

Velocity

Angle of attack

Angle of attack is thedifference between pitchattitude and flight path angle(assumes no wind).

Pitchattitude

Flight path angle

Flight pathvector

SECTION 2

2.19

the ground speed is known. Many standard instru-ment departures require knowledge of flight pathangle in order to ensure obstacle clearance.

Angle of attack is also the difference between thepitch angle and the flight path angle in a no-windcondition. The angle of attack determines whetherthe aerodynamic surfaces on the airplane are stalledor not.

The important point is that when the angle of attackis above the stall angle, the lifting capability of thesurface is diminished. This is true regardless ofairspeed. An airplane wing can be stalled at anyairspeed. An airplane can be stalled in any attitude.If the angle of attack is greater than the stall angle,the surface will stall. Figure 19 indicates thatregardless of the airspeed or pitch attitude of theairplane, the angle of attack determines whetherthe wing is stalled.

A stall is characterized by any or a combination ofthe following:• Buffeting, which could be heavy.• Lack of pitch authority.• Lack of roll control.• Inability to arrest descent rate.

These characteristics are usually accompanied bya continuous stall warning. A stall must not beconfused with an approach-to-stall warning thatoccurs before the stall and warns of an approach-ing stall. An approach to stall is a controlled flightmaneuver. However, a full stall is an out-of-con-trol condition, but it is recoverable.

Stall speeds are published in the AFM for eachtransport airplane, giving the speeds at which theairplane will stall as a function of weight. Thisinformation is very important to the pilot, but itmust be understood that the concept of stall speedis very carefully defined for specific conditions:• Trim at 1.3 Vs.• Forward CG.• Low altitudes.• Deceleration rate of 1 kn/s.• Wings level.• Approximately 1-g flight.

Under normal conditions, the wings are level ornear level, and the normal load factor is very near1.0. Under these conditions, the published stallspeeds give the pilot an idea of the proximity to

Figure 19Several PitchAttitudes and StallAngle of Attack

Velocity

High AOA

High AOA

Velocity

Velocity

HighAOA

The wing only “knows”angle of attack (AOA).

HighAOA

Velocity

Horizon

SECTION 2

2.20

stall. In conditions other than these, however, thespeed at stall is not the same as the “stall speed.”Aerodynamic stall depends only on angle of at-tack, and it has a specific relationship to stall speedonly under the strict conditions previously noted.Many upsets are quite dynamic in nature andinvolve elevated load factors and large speed-change rates. Pilots should not expect the airplaneto remain unstalled just because the indicatedairspeed is higher than AFM chart speeds, becausethe conditions may be different.

All modern jet transports are certified to exhibitadequate warning of impending stall, to give thepilot opportunity to recover by decreasing theangle of attack. Whether this warning is by naturalaerodynamic buffet or provided by a stick shakeror other warning devices, it warns the pilot whenthe angle of attack is getting close to stall. More-over, the warning is required to be in a form otherthan visual. The pilot need not look at a particularinstrument, gauge, or indicator. The warning istactile: the pilot is able to feel the stall warningwith enough opportunity to recover promptly. Pi-lots need to be especially cognizant of stall warn-ing cues for the particular airplanes they fly. Theonset of stall warning should be taken as an indica-tion to not continue to increase the angle of attack.

The angle of attack at which a wing stalls reduceswith increasing Mach so that at high Mach (nor-mally, high altitude), an airplane may enter anaccelerated stall at an angle of attack that is lessthan the angle of attack for stalling at lower Machnumbers.

2.5.5.2 Camber

Camber refers to the amount of curvature evidentin an airfoil shape. Camber is illustrated inFigure 20. The mean camber line is a line connect-ing the midpoints of upper and lower surfaces of anairfoil. In contrast, the chord line is a straight lineconnecting the leading and trailing edges.

Technical aerodynamicists have defined camberin a variety of ways over the years, but the reasonfor introducing camber has remained the same:airfoils with camber are more efficient at produc-ing lift than those without. Importantly, airfoilswith specific kinds of camber at specific places aremore efficient than those of slightly different shape.

Airplanes that must produce lift as efficiently up aswell as down, such as competition aerobatics air-planes, usually employ symmetrical airfoils. Thesework well, but they are not as efficient for cruiseflight. Efficient, high-speed airplanes often em-

Figure 20Camber

Definition

Symmetrical Airfoil Modern Aft-Cambered Airfoil

Cambered Airfoil

Trailing edge

Mean camber line

Chord line

Leading edge

SECTION 2

2.21

ploy exotic camber shapes because they have beenfound to have beneficial drag levels at high speeds.Depending on the mission the airplane is intendedto fly, the aerodynamic surfaces are given anoptimized camber shape. While both camberedand uncambered surfaces produce lift at angle ofattack, camber usually produces lift more effi-ciently than angle of attack alone.

2.5.5.3 Control Surface Fundamentals

Trailing edge control surfaces such as ailerons,rudders, and elevators provide a way of modulat-ing the lift on a surface without physically chang-ing the angle of attack. These devices work byaltering the camber of the surfaces. Figure 21shows undeflected and deflected control surfaces.

The aerodynamic effect is that of increasing the liftat constant angle of attack for trailing edge downdeflection. This is shown in Figure 22. The pricepaid for this increased lift at constant angle of

attack is a reduced angle of attack for stall. Notethat for larger deflections, even though the lift isgreater, the stall angle of attack is lower than thatat no deflection.

The important point is that increasing camber(downward deflection of ailerons, for example)lowers the angle of attack at which stall occurs.Large downward aileron deflections at very highangles of attack could induce air separation overthat portion of the wing. Reducing the angle ofattack before making large aileron deflections willhelp ensure that those surfaces are as effective asthey can be in producing roll.

2.5.5.3.1 Spoiler-Type Devices

Spoilers, sometimes referred to as “speedbrakes”on large transport airplanes, serve a dual purposeof “spoiling” wing lift and generating additionaldrag. By hinging upwards from the wing uppersurface, they generate an upper surface disconti-

Figure 21DeflectedSurfaces

Figure 22Lift Characteristicsfor DeflectedTrailing EdgeSurfaces

Effective mean camber line

Control surfacedeflection

Control surfacedeflectionLift

coefficient

Angle ofattack

Angle of attack

No deflection

Deflected control Stall

Relative wind

SECTION 2

2.22

nuity that the airflow cannot negotiate, and theyseparate, or stall, the wing surface locally. Figure23 depicts spoiler operation with both flaps up andflaps down. The effectiveness of spoiler devicesdepends on how much lift the wing is generating(which the spoiler will “spoil”). If the wing is notproducing much lift to begin with, spoiling it willnot produce much effect. If the wing is producinglarge amounts of lift, as is the case with the flapsextended and at moderate angles of attack, thespoilers become very effective control devicesbecause there is more lift to spoil.

Because spoilers depend on there being some liftto “spoil” in order to be effective, they also losemuch of their effectiveness when the wing is in astalled condition. If the flow is already separated,putting a spoiler up will not induce any moreseparation. As was the case with aileron control athigh angles of attack, it is important to know thatthe wing must be unstalled in order for the aerody-namic controls to be effective.

2.5.5.3.2 Trim

Aerodynamicists refer to “trim” as that conditionin which the forces on the airplane are stabilizedand the moments about the center of gravity all addup to zero. Pilots refer to “trim” as that conditionin which the airplane will continue to fly in themanner desired when the controls are released. Inreality, both conditions must be met for the air-plane to be “in trim.” In the pitch axis, aerody-namic, or moment, trim is achieved by varying thelift on the horizontal tail/elevator combination tobalance the pitching moments about the center ofgravity. Once the proper amount of lift on the tailis achieved, means must be provided to keep itconstant. Traditionally, there have been three waysof doing that: fixed stabilizer/trim tab, all-flyingtail, and trimmable stabilizer.

In the case of the fixed stabilizer/trim tab configu-ration, the required tail load is generated by de-flecting the elevator. The trim tab is then deflected

Figure 24Typical

TrimmableTails Maximum deflection

Smaller additionaldeflection available,this direction

Deflected trim tab holds surface away from neutral position

Larger additionaldeflection available,this direction

Maximum deflection

Figure 23Spoiler Devices

Separationregion

Separationregion

Flaps Up Flaps Down

Spoiler deflectedSpoiler deflected

SECTION 2

2.23

in such a way as to get the aerodynamics of the tabto hold the elevator in the desired position. Theairplane is then in trim (because the required loadon the tail has been achieved) and the column forcetrim condition is met as well (because the tab holdsthe elevator in the desired position). One sideeffect of this configuration is that when trimmednear one end of the deflection range, there is notmuch more control available for maneuvering inthat direction (Fig. 24).

In the case of the all-flying tail, the entire stabilizermoves as one unit in response to column com-mands. This changing of the angle of attack of thestabilizer adjusts the tail lift as required to balancethe moments. The tail is then held in the desiredposition by an irreversible flight control system(usually hydraulic). This configuration requires avery powerful and fast-acting control system tomove the entire tail in response to pilot inputs, butit has been used quite successfully on commercialjet transport airplanes.

In the case of the trimmable stabilizer, the properpitching moment is achieved by deflecting theelevator and generating the required lift on the tail.The stabilizer is then moved (changing its angle ofattack) until the required tail lift is generated by thestabilizer with the elevator essentially at zero de-flection. A side effect of this configuration is thatfrom the trimmed condition, full elevator deflec-tion is available in either direction, allowing amuch larger range of maneuvering capability. Thisis the configuration found on most high-perfor-mance airplanes that must operate through a verywide speed range and that use very powerful high-lift devices (flaps) on the wing.

Knowing that in the trimmed condition the eleva-tor is nearly faired or at zero deflection, the pilotinstantly knows how much control power is avail-able in either direction. This is a powerful tactilecue, and it gives the pilot freedom to maneuverwithout the danger of becoming too close to sur-face stops.

2.5.5.4 Lateral and Directional Aerodynamic Considerations

Aerodynamically, anti-symmetric flight, or flightin sideslip can be quite complex. The forces andmoments generated by the sideslip can affect mo-tion in all three axes of the airplane. As will beseen, sideslip can generate strong aerodynamicrolling moments as well as yawing moments. In

particular the magnitude of the coupled roll-due-to-sideslip is determined by several factors.

2.5.5.4.1 Angle of Sideslip

Just as airplane angle of attack is the angle betweenthe longitudinal axis of the airplane and the rela-tive wind as seen in a profile view, the sideslipangle is the angle between the longitudinal axis ofthe airplane and the relative wind, seen this time inthe plan view (Fig. 25). It is a measure of whetherthe airplane is flying straight into the relative wind.

With the exception of crosswind landing consider-ations requiring pilot-commanded sideslip, com-mercial transport airplanes are typically flown ator very near zero sideslip. This usually results inthe lowest cruise drag and is most comfortable forpassengers, as the sideways forces are minimized.

For those cases in which the pilot commands asideslip, the aerodynamic picture becomes a bitmore complex. Figure 25 depicts an airplane in a

Figure 25Angle of Sideslip

Left rudder,right aileron/spoiler

“Cross-controlled”

Rudder deflected leftto hold sideslip angle

Aileron upAileron down

Spoilers up

Sideslipangle

Airp

lane

vel

ocity

Rel

ativ

e w

ind

Rel

ativ

e w

ind

SECTION 2

2.24

commanded nose-left sideslip. That is, the veloc-ity vector is not aligned with the longitudinal axisof the airplane, and the relative wind is comingfrom the pilot’s right.

One purpose of the vertical tail is to keep the noseof the airplane “pointed into the wind,” or make thetail follow the nose. When a sideslip angle isdeveloped, the vertical tail is at an angle of attackand generates “lift” that points sideways, tendingto return the airplane to zero sideslip. Commercialjet transport airplanes are certificated to exhibitstatic directional stability that tends to return theairplane to zero sideslip when controls are releasedor returned to a neutral position. In order to hold asideslip condition, the pilot must hold the rudder ina deflected position (assuming symmetrical thrust).

2.5.5.4.2 Wing Dihedral Effects

Dihedral is the positive angle formed between thelateral axis of an airplane and a line that passesthrough the center of the wing, as depicted inFigure 26. Dihedral contributes to the lateral sta-bility of an airplane, and commercial jet transportairplanes are certificated to exhibit static lateralstability. A wing with dihedral will develop stablerolling moments with sideslip. If the relative windcomes from the side, the wing into the wind issubject to an increase in lift. The wing away fromthe wind is subject to a decrease in angle of attackand develops a decrease in lift. The changes in lifteffect a rolling moment, tending to raise the wind-ward wing; hence, dihedral contributes a stableroll due to sideslip. Since wing dihedral is sopowerful in producing lateral stability, it is used asa “common denominator term” of the lateral sta-bility contribution of other airplane components,such as rudder and wing sweep. In other words, the

term “dihedral effect” is used when describing theeffects of wing sweep and rudder on lateral stabil-ity and control.

A swept-wing design used on jet transport air-planes is beneficial for high-speed flight, sincehigher flight speeds may be obtained before com-ponents of speed perpendicular to the leading edgeproduce critical conditions on the wing. In otherwords, wing sweep will delay the onset of com-pressibility effects. This wing sweep also contrib-utes to the dihedral effect. When the swept-wingairplane is placed in a sideslip, the wing into thewind experiences an increase in lift, since theeffective sweep is less, and the wing away from thewind produces less lift, since the effective sweep isgreater (Fig. 25). The amount of contribution, ordihedral effect, depends on the amount ofsweepback and lift coefficient of the wing. Theeffect becomes greater with increasing lift coeffi-cient and wing sweep. The lift coefficient willincrease with increasing angle of attack up to thecritical angle. This means that any sideslip resultsin more rolling moment on a swept-wing airplanethan on a straight-wing airplane. Lateral controlson swept-wing airplanes are powerful enough tocontrol large sideslip angles at operational speeds.

Rudder input produces sideslip and contributes tothe dihedral effect. The effect is proportional to theangle of sideslip. (That is, roll increases withsideslip angle; therefore, roll increases with in-creasing rudder input.) When an airplane is at ahigh angle of attack, aileron and spoiler roll con-trols become less effective. At the stall angle ofattack, the rudder is still effective; therefore, it canproduce large sideslip angles, which in turn pro-duces roll because of the dihedral effect.

Figure 26Wing Dihedral

Angle

Dihedral angle

SECTION 2

2.25

2.5.5.4.3 Pilot-Commanded Sideslip

It is important to keep in mind that the rudders onmodern jet transport airplanes are usually sized tocounter the yawing moment associated with anengine failure at very low takeoff speeds. This verypowerful rudder is also capable of generating largesideslips (when an engine is not failed). The largesideslip angles generate large rolling moments thatrequire significant lateral control input to stop theairplane from rolling. In maneuvering the airplane,if a crosswind takeoff or landing is not involvedand an engine is not failed, keeping the sideslip asclose to zero as possible ensures that the maximumamount of lateral control is available for maneu-vering. This requires coordinated use of bothaileron/spoilers and rudder in all maneuvering.

One way to determine the sideslip state of theairplane is to “feel” the lateral acceleration; it feelsas if the pilot is being pushed out of the seatsideways. Another way is to examine the slip-skidindicator and keep the ball in the center. Pilotsshould develop a feel for the particular airplanesthey fly and understand how to minimize sideslipangle through coordinated use of flight controls.

Crossover speed is a recently coined term thatdescribes the lateral controllability of an airplanewith the rudder at a fixed (up to maximum) deflec-tion. It is the minimum speed (weight and configu-ration dependent) in a 1-g flight, where maximumaileron/spoiler input (against the stops) is reachedand the wings are still level or at an angle tomaintain directional control. Any additional rud-der input or decrease in speed will result in anunstoppable roll into the direction of the deflectedrudder or in an inability to maintain desired head-ing. Crossover speed is very similar in concept toVmca, except that instead of being Vmc due to athrust asymmetry, it is Vmc due to full rudderinput. This crossover speed is weight and configu-ration dependent. However, it is also sensitive toangle of attack. With weight and configurationheld constant, the crossover speed will increasewith increased angle of attack and will decreasewith decreased angle of attack. Thus, in an airplaneupset due to rudder deflection with large andincreasing bank angle and the nose rapidly fallingbelow the horizon, the input of additional nose-upelevator with already maximum input of aileron/spoilers will only aggravate the situation. Thecorrect action in this case is to unload the airplane

to reduce the angle of attack, which will regainaileron/spoiler effectiveness and allow recovery.This action may not be intuitive and will result ina loss of altitude.

Note: The previous discussion refers to the aero-dynamic effects associated with rudder input; how-ever, similar aerodynamic effects are associatedwith other surfaces.

2.5.5.5 High-Speed, High-AltitudeCharacteristics

Modern commercial jet transport airplanes aredesigned to fly at altitudes from sea level to morethan 40,000 ft. There are considerable changes inatmospheric characteristics that take place overthat altitude range, and the airplane must accom-modate those changes.

One item of interest to pilots is the air temperatureas altitude changes. Up to the tropopause (36,089 ftin a standard atmosphere), the standard tempera-ture decreases with altitude. Above the tropo-pause, the standard temperature remains relativelyconstant. This is important to pilots because thespeed of sound in air is a function only of airtemperature. Aerodynamic characteristics of lift-ing surfaces and entire airplanes are significantlyaffected by the ratio of the airspeed to the speed ofsound. That ratio is Mach number. At high alti-tudes, large Mach numbers exist at relatively lowcalibrated airspeeds.

As Mach number increases, airflow over parts ofthe airplane begins to exceed the speed of sound.Shock waves associated with this local supersonicflow can interfere with the normally smooth flowover the lifting surfaces, causing local flow sepa-ration. Depending on the airplane, as this separa-tion grows in magnitude with increasing Machnumber, characteristics such as pitchup, pitchdown,or aerodynamic buffeting may occur. Transportcategory airplanes are certificated to be free fromcharacteristics that would interfere with normalpiloting in the normal flight envelope and to besafely controllable during inadvertent exceedancesof the normal envelope, as discussed in Section2.5.4, “Aerodynamic Flight Envelope.”

The point at which buffeting would be expected tooccur is documented in the Approved FlightManual. The Buffet Boundary or Cruise Maneuver

SECTION 2

2.26

Capability charts contain a wealth of informationabout the high-altitude characteristics of each air-plane. A sample of such a chart is shown inFigure 27.

The chart provides speed margins to low-speed(stall-induced) and high-speed (shock-induced)buffet at 1 g, normal load factor or bank angle tobuffet at a given Mach number, or altitude capabil-ity at a given Mach number and 1 g. The buffetboundaries of various airplanes can differ signifi-cantly in their shapes, and these differences con-tain valuable information for the pilot. Someairplanes have broad speed margins, some haveabrupt high-speed buffet margins, some have nar-row, “peaky” characteristics, as depicted notion-ally in Figure 28. Pilots should become familiarwith the buffet boundaries. These boundaries letthe pilot know how much maneuvering room isavailable, and they give clues for successful strat-

egies should speed changes become rapid or atti-tude or flight path angles become large.

For example, the pilot of Airplane A in the figurehas a broad speed range between high- and low-speed buffet onset at 1 g and the current altitude,with only a nominal g capability. Airplane B hasby comparison a much smaller speed range be-tween high- and low-speed buffet onset, but agenerous g capability at the current Mach number.Airplane C is cruising much closer to the high-speed buffet boundary than the low-speed bound-ary, which lets the pilot know in which direction(slower) there is more margin available.

2.5.5.6 Stability

Positive static stability is defined as the initialtendency to return to an undisturbed state after adisturbance. This concept has been illustrated bythe “ball in a cup” model (Fig. 29).

Figure 27Sample Buffet

Boundary Chart

0.45

35 36 37 38 39 40 41 42 43

0.50 0.55 0.60

60

65

70

75

80

85

90

95

100

105

110

0.65 0.70 0.75 0.80

High-speedmargin

Low-speedmargin

0.85 10 20 30 40 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0

60555045403530252015

True Mach number (MT) CG percent MAC

Ref

. lin

e

Ban

k an

gle,

deg

Normal acceleration to initial buffet, g

Gro

ss w

eigh

t, kg

x 1

000

0

Altitude x 1000

Altitude margin

Figure 28Notional Buffet

Boundaries

Mach

Airplane A Airplane B Airplane CMach Mach

Cruise altitude

Coe

ffici

ent o

f lift

Coe

ffici

ent o

f lift

Coe

ffici

ent o

f lift

Cruise altitudeCruise altitude

SECTION 2

2.27

All transport airplanes demonstrate positive sta-bility in at least some sense. The importance hereis that the concept of stability can apply to anumber of different parameters, all at the sametime. Speed stability, the condition of an airplanereturning to its initial trim airspeed after a distur-bance, is familiar to most pilots. The same conceptapplies to Mach number. This stability can beindependent of airspeed if, for example, the air-plane crosses a cold front. When the outside airtemperature changes, the Mach number changes,even though the indicated airspeed may not change.Airplanes that are “Mach stable” will tend to returnto the original Mach number. Many jet transportairplanes incorporate Mach trim to provide thisfunction. Similarly, commercial airplanes are stablewith respect to load factor. When a gust or otherdisturbance generates a load factor, the airplane iscertificated to be stable: it will return to its initialtrimmed load factor (usually 1.0). This “maneu-

vering stability” requires a sustained pull force toremain at elevated load factors—as in a steep turn.

One important side effect of stability is that itallows for some unattended operation. If the pilotreleases the controls for a short period of time,stability will help keep the airplane at the conditionat which it was left.

Another important side effect of stability is that oftactile feedback to the pilot. On airplanes withstatic longitudinal stability, for example, if thepilot is holding a sustained pull force, the speed isprobably slower than the last trim speed.

2.5.5.7 Maneuvering in Pitch

Movement about the lateral axis is called “pitch,”as depicted in Figure 30.

Figure 29Static Stability

Unstable NeutralStableWhen ball is displaced,it returns to its original position.

When ball is displaced,it accelerates from its original position.

When ball is displaced,it neither returns, nor accelerates away—itjust takes up a newposition.

Figure 30Reference AxisDefinitions

Lateral axis

Ver

tical

axi

s

Longitudinal

axis

Center ofgravity

Pitch

SECTION 2

2.28

Controlling pitching motions involves controllingaerodynamic and other moments about the centerof gravity to modulate the angle of attack. Asidefrom the pitching moment effects of thrust whenengines are offset from the center of gravity (dis-cussed below), the pilot controls the pitching mo-ments (and therefore the angle of attack) by meansof the stabilizer and elevator. The horizontal stabi-lizer should be thought of as a trimming device,reducing the need to hold elevator deflection,while the elevator should be thought of as theprimary maneuvering control. This is true becausethe horizontal stabilizer has only limited rate capa-bility—it cannot change angle very quickly. Ma-neuvering, or active pilot modulation of the pitchcontrols, is usually accomplished by the elevatorcontrol, which is designed to move at much fasterrates. To get a better understanding of how thesecomponents work together, the following discus-sion will examine the various components of pitch-ing moment.

“Moments” have dimensions of force times dis-tance. Pilots are familiar with moments from work-ing weight and balance problems. In the case ofpitching moment, we are concerned with momentsabout the center of gravity. So the pitching mo-ment due to wing lift, for example, is the wing lift

times the distance between the center of gravityand the center of the wing lift. Since weight actsthrough the center of gravity, there is no momentassociated with it. In addition, there is a momentassociated with the fact that the wing is usuallycambered and with the fact that the fuselage isflying in the wing’s flowfield. This wing-bodymoment does not have a force associated with it; itis a pure torque.

Figure 31 shows many of the important compo-nents of pitching moment about the center ofgravity of an airplane. Weight acts through thecenter of gravity and always points toward thecenter of the Earth. In steady (unaccelerated) flight,the moments about the center of gravity, as well asthe forces, are all balanced: the sum is zero. Since,in general, there is a pitching moment due to thewing and body and the lift is not generally alignedwith the center of gravity—and the thrust of theengines is also offset from the center of gravity—there is usually some load on the horizontal tailrequired to balance the rest of the moments, andthat load is generally in the downward direction, asshown in the figure.

Essentially, the pilot controls the amount of liftgenerated by the horizontal tail (by moving the

Figure 31Airplane Pitching

Moments

Tail lift

Weight

Lift

Wing distance

Enginedistance

ThrustTail distance

Drag

Wing-bodymoment

(Moment)Tail

(Moment)Lift

(Moment)Thrust

(Moment) =Wing-body

(Moment)Wing-body

Totalpitchingmoment

=Totalpitchingmoment

+ + +

+Tail Tail + +* * *liftWing Wing

distancelift distanceThrust Engine

distance

SECTION 2

2.29

elevator), which adjusts the angle of attack of thewing and therefore modulates the amount of liftthat the wing generates. Similarly, since enginesare rarely aligned with the center of gravity, chang-ing the thrust will be accompanied by a change inthe pitching moment around the center of gravity.The pilot then adjusts the lift on the tail (with theelevator) to again balance the pitching moments.

As long as the angle of attack is within unstalledlimits and the airspeed is within limits, the aerody-namic controls will work to maneuver the airplanein the pitch axis as described. This is true regard-less of the attitude of the airplane or the orientationof the weight vector.

Recall that the object of maneuvering the airplaneis to manipulate the forces on the airplane in orderto manage the energy state. The aerodynamicforces are a function of how the pilot manipulatesthe controls, changing angle of attack, for ex-ample. Similarly, the thrust forces are commandedby the pilot. The weight vector always pointstoward the center of the Earth. The orientation withrespect to the airplane, though, is a function of theairplane attitude. The weight vector is a verypowerful force. Recall that transport airplanes arecertificated to 2.5 g. That means that the wing is

capable of generating 2.5 times the airplane weight.In contrast, engine thrust is typically on the orderof 0.3 times the airplane weight at takeoff weights.

To get an appreciation for the magnitude of theweight vector and the importance of its orienta-tion, consider the very simple example ofFigure 32.

In a nose-up pitch attitude, the component of theweight vector in the drag direction (parallel to theairplane longitudinal axis) equals the engine thrustat about 20 deg, nose-up pitch attitude on a takeoffclimb. Conversely, at nose-down pitch attitudes,the weight vector contributes to thrust. Since themagnitude of the weight vector is on the order of 3times the available thrust, pilots need to be verycareful about making large pitch attitude changes.When procedures call for a pitch attitude reductionto accelerate and clean up after takeoff, one aspectof that maneuver is getting rid of the weight com-ponent in the drag direction, allowing the airplaneto gain speed.

2.5.5.8 Mechanics of Turning Flight

Recalling that Newton’s laws dictate that an objectin motion will continue in a straight line unless

Figure 32Contributions ofWeight Vector

Weight

Component of weightin drag direction

Component of weightin thrust direction

Thrust

Thrust

SECTION 2

2.30

acted on by an external force, consider what isrequired to make an airplane turn. If a pilot wantsto change the course of an airplane in flight, a forceperpendicular to the flight path in the direction ofthe desired turn must first be generated. Usuallythis is accomplished by banking the airplane. Thispoints the lift vector off to the side, generating ahorizontal component of lift (Fig. 33). This is notthe only way to generate a sideways-pointing force,but it is the typical method.

When the lift vector is tilted to generate the hori-zontal component, the vertical component getssmaller. Since the acceleration due to gravity stillpoints toward the earth, there is now an imbalancein the vertical forces. Unless the lift vector isincreased so that its vertical component equals theweight of the airplane, the airplane will begin toaccelerate toward the earth—it will begin to de-scend. To maintain altitude in a banked turn, thelift produced by the airplane must be more than the

weight of the airplane, and the amount is a functionof bank angle (Fig. 34).

All of this is well known, but it bears reiteration inthe context of recovery from extreme airplaneupsets. If the objective is to arrest a descent,maneuvering in pitch if the wings are not level willonly cause a tighter turn and, depending on thebank angle, may not contribute significantly togenerating a lift vector that points away from theground. Indeed, Figure 34 indicates that to main-tain level flight at bank angles beyond 66 degrequires a larger load factor than that for whichtransport airplanes are certificated.

In early training, many pilots are warned about the“Graveyard Spiral.” The Graveyard Spiral maneu-ver is one in which the airplane is in a large bankangle and descending. The unknowing pilot fix-ates on the fact that airspeed is high and theairplane is descending. In an attempt to arrest both

Figure 33Mechanics of

Turning Flight

Figure 34Bank Versus Load

Factor (g’s) forLevel Flight

Weight

Lift

Additionallift required so that vertical componentstill equals weight

Horizontal componentproduces curvedflight path = turn

4

3

2

1

3020100 5040 60 70

Loadfactor, g's

Bank angle, deg

SECTION 2

2.31

the speed and sinkrate, the pilot pulls on the col-umn and applies up-elevator. However, at a largebank angle, the only effect of the up-elevator is tofurther tighten the turn. It is imperative to get thewings close to level before beginning any aggres-sive pitching maneuver. This orients the lift vectoraway from the gravity vector so that the forcesacting on the airplane can be managed in a con-trolled way.

Knowledge of these relationships is useful in othersituations as well. In the event that the load factoris increasing, excess lift is being generated, and thepilot does not want speed to decrease, bank anglecan help to keep the flight path vector below thehorizon, getting gravity to help prevent loss ofairspeed. In this situation, the excess lift can beoriented toward the horizon and, in fact, modu-lated up and down to maintain airspeed.

2.5.5.9 Lateral Maneuvering

Motion about the longitudinal axis (Fig. 35) iscalled “roll.” Modern jet transport airplanes usecombinations of aileron and spoiler deflections asprimary surfaces to generate rolling motion. Thesedeflections are controlled by the stick or wheel,and they are designed to provide precise maneu-vering capability. On modern jet airplanes, thespecific deflection combinations of ailerons andspoilers are usually designed to make adverse yawvirtually undetectable to the pilot. Even so, coor-dinated use of rudder in any lateral maneuveringshould keep sideslip to a minimum.

As described in Section 2.5.5, “Aerodynamics,”trailing edge control surfaces lose effectiveness inthe downgoing direction at high angles of attack.Similarly, spoilers begin to lose effectiveness asthe stall angle of attack is exceeded.

Transport airplanes are certificated to have posi-tive unreversed lateral control up to a full aerody-namic stall. That is, during certification testing,the airplane has been shown to have the capabilityof producing and correcting roll up to the time theairplane is stalled. However, beyond the stall angleof attack, no generalizations can be made. For thisreason it is critical to reduce the angle of attackat the first indication of stall so that controlsurface effectiveness is preserved.

The apparent effectiveness of lateral control, thatis, the time between the pilot input and when theairplane responds, is in part a function of the

airplane’s inertia about its longitudinal axis. Air-planes with very long wings, and, in particular,airplanes with engines distributed outboard alongthe wings, tend to have very much larger inertiasthan airplanes with engines located on the fuse-lage. This also applies to airplanes in which fuel isdistributed along the wing span. Early in a flightwith full wing (or tip) tanks, the moment of inertiaabout the longitudinal axis will be much largerthan when those tanks are nearly empty. Thisgreater inertia must be overcome by the rollingmoment to produce a roll acceleration and result-ing roll angle, and the effect is a “sluggish” initialresponse. As discussed before, airplanes of largemass and large inertia require that pilots be pre-pared for this longer response time and plan appro-priately in maneuvering.

From a flight dynamics point of view, the greatestpower of lateral control in maneuvering the air-plane—in using available energy to maneuver theflight path—is to orient the lift vector. In particu-lar, pilots need to be aware of their ability to orientthe lift vector with respect to the gravity vector.Upright with wings level, the lift vector is opposedto the gravity vector, and vertical flight path iscontrolled by longitudinal control and thrust. Up-right with wings not level, the lift vector is notaligned with gravity, and the flight path will becurved. In addition, if load factor is not increasedbeyond 1.0, that is, if lift on the wings is not greaterthan weight, the vertical flight path will becomecurved in the downward direction, and the airplanewill begin to descend. Hypothetically, with theairplane inverted, lift and gravity point in the samedirection: down. The vertical flight path will be-

Figure 35Roll Axis

Lateral axis

Ver

tical

axi

s

Longitudinal

axis

Center ofgravity

Roll

SECTION 2

2.32

come curved and the airplane will accelerate to-ward the earth quite rapidly. In this case, the pilotmust find a way to orient the lift vector away fromgravity. In all cases, the pilot should ensure that theangle of attack is below the stall angle and roll toupright as rapidly as possible.

2.5.5.10 Directional Maneuvering

Motion about the vertical axis is called “yaw”(Fig. 36). The character of the motion about thevertical axis is determined by the balance of mo-ments about the axis (around the center of gravity).The principal controller of aerodynamic momentsabout the vertical axis is the rudder, but it is not theonly one. Moments about the vertical axis can begenerated or affected by asymmetric thrust, or byasymmetric drag (generated by ailerons, spoilers,asymmetric flaps, and the like). These asymmetricmoments may be desired (designed in) or unde-sired (perhaps the result of some failure).

Generally, the rudder is used to control yaw in away that minimizes the angle of sideslip, that is,the angle between the airplane’s longitudinal axisand the relative wind. For example, when an en-gine fails on takeoff, the object is to keep theairplane aligned with the runway by using rudder.

On modern jet transports with powerful engineslocated away from the centerline, an engine failurecan result in very large yawing moments, andrudders are generally sized to be able to controlthose moments down to very low speeds. Thismeans that the rudder is very powerful and has thecapability to generate very large yawing moments.When the rest of the airplane is symmetric, for

example, in a condition of no engine failure, verylarge yawing moments would result in very largesideslip angles and large structural loads, shouldthe pilot input full rudder when it is not needed.Pilots need to be aware of just how powerful therudder is and the effect it can have when the rest ofthe airplane is symmetric. Many modern airplaneslimit the rudder authority in parts of the flightenvelope in which large deflections are not re-quired, for example, at high speeds. In this way, thesupporting structure can be made lighter. Pilotsalso need to be aware of such “rudder limiting”systems and how they operate on airplanes.

There are a few cases, however, when it is neces-sary to generate sideslip. One of the most commonis the crosswind landing. In the slip-to-a-landingtechnique, simultaneous use of rudder and aileron/spoiler aligns the airplane with the runwaycenterline and at the same time keeps the airplanefrom drifting downwind. The airplane is flying“sideways” and the pilot feels the lateralacceleration.

Static stability in the directional axis tends to drivethe sideslip angle toward zero. The vertical fin andrudder help to do this. The number of times theairplane oscillates as it returns to zero sideslipdepends on its dynamic stability. Most of thedynamic stability on a modern transport comes,not from the natural aerodynamics, but from anactive stability augmentation system: the yawdamper. If disturbed with the yaw damper off, theinertial and aerodynamic characteristics of a mod-ern jet transport will result in a rolling and yawingmotion referred to as “dutch roll.” The yaw dampermoves the rudder to oppose this motion and dampit out very effectively. Transport airplanes arecertificated to demonstrate positively dampeddutch-roll oscillations.

The installed systems that can drive the ruddersurface are typically designed in a hierarchicalmanner. For example, the yaw damper typicallyhas authority to move the rudder in only a limiteddeflection range. Rudder trim, selectable by thepilot, has authority to command much larger rud-der deflections that may be needed for enginefailure. In most cases, the pilot, with manual con-trol over rudder deflection, is the most powerfulelement in the system. The pilot can commanddeflection to the limits of the system, which maybe surface stops, actuator force limits, or anyothers that may be installed (e.g., rudder ratiochangers).

Figure 36Yaw Axis

Lateral axis

Ver

tical

axi

s

Longitudinal

axis

Center ofgravity

Yaw

SECTION 2

2.33

2.5.5.11 Flight at Extremely Low Airspeeds

Stall speed is discussed in Section 2.5.5.1. It ispossible for the airplane to be flown at speedsbelow the defined stall speed. This regime is out-side the certified flight envelope. At extremely lowairspeeds, there are several important effects forthe pilot to know.

Recall from the discussion of aerodynamics thatthe aerodynamic lift that is generated by wings andtails depends on both the angle of attack and thevelocity of the air moving over the surfaces. Angleof attack alone determines whether the surface isstalled. At very low airspeeds, even far below thestrictly defined stall speed, an unstalled surface(one at a low angle of attack) will produce lift.However, the magnitude of the lift force willprobably be very small. For a surface in thiscondition, the lift generated will not be enough tosupport the weight of the airplane. In the case of thelift generated by the tail, at very low airspeeds, itmay not be great enough to trim the airplane, thatis, to keep it from pitching.

With small aerodynamic forces acting on the air-plane, and gravity still pulling towards the earth,the trajectory will be largely ballistic. It may bedifficult to command a change in attitude untilgravity produces enough airspeed to generate suf-ficient lift—and that is only possible at angles ofattack below the stall angle. For this reason, ifairspeed is decreasing rapidly it is very importantto reduce angle of attack and use whatever aerody-namic forces are available to orient the airplane sothat a recovery may be made when sufficientforces are available.

When thrust is considered, the situation becomesonly slightly more complicated. With engines off-set from the center of gravity, thrust produces bothforces and moments. In fact, as airspeed decreases,engine thrust generally increases for a given throttlesetting. With engines below the center of gravity,there will be a nose-up moment generated byengine thrust. Especially at high power settings,this may contribute to even higher nose-up atti-tudes and even lower airspeeds. Pilots should beaware that as aerodynamic control effectivenessdiminishes with lower airspeeds, the forces andmoments available from thrust become more evi-dent, and until the aerodynamic control surfacesbecome effective, the trajectory will depend largelyon inertia and thrust effects.

2.5.5.12 Flight at Extremely High Speeds

Inadvertent excursions into extremely high speeds,either Mach number or airspeed, should be treatedvery seriously. As noted in the section on high-speed, high-altitude aerodynamics (Sec. 2.5.5.5),flight at very high Mach numbers puts the airplanein a region of reduced maneuvering envelope (closerto buffet boundaries). Many operators opt to fly atvery high altitudes, because of air traffic control(ATC) and the greater efficiencies afforded there.But operation very close to buffet-limiting alti-tudes restricts the range of Mach numbers and loadfactors available for maneuvering. During certifi-cation, all transport airplanes have been shown toexhibit safe operating characteristics with inad-vertent exceedances of Mach envelopes. Theseexceedances may be caused by horizontal gusts,penetration of jet stream or cold fronts, inadvertentcontrol movements, leveling off from climb, de-scent from Mach-limiting to airspeed-limiting al-titudes, gust upsets, and passenger movement.This means that the controls will operate normallyand airplane responses are positive and predictablefor these conditions. Pilots need to be aware thatthe maneuvering envelope is small and that pru-dent corrective action is necessary to avoid ex-ceeding the other end of the envelope duringrecovery. Pilots should become very familiar withthe high-speed buffet boundaries of their airplaneand the combinations of weights and altitudes atwhich they operate.

Flight in the high-airspeed regime brings with it anadditional consideration of very high control power.At speeds higher than maneuver speed (Fig. 14),very large deflection of the controls has the poten-tial to generate structural damage. While promptcontrol input is required to reduce speed after aninadvertent exceedance, care must be taken toavoid damage to the airplane. Pilots should beknowledgeable of the load factor envelope of theirairplane.

In either the Mach or airspeed regime, if speed isexcessive, the first priority should be to reducespeed to within the normal envelope. Many toolsare available for this, including orienting the liftvector away from the gravity vector; adding loadfactor, which increases drag; reducing thrust; andadding drag by means of the speedbrakes. Asdemonstrated in Section 2.5.5.8, “Mechanics ofTurning Flight,” the single most powerful forcethe pilot has available is the wing lift force. The

SECTION 2

2.34

second largest force acting on the airplane is theweight vector. Getting the airplane maneuvered sothat the lift vector points in the desired directionshould be the first priority, and it is the first steptoward managing the energy available in theairplane.

2.6 Recovery From Airplane UpsetsPrevious sections of this training aid review thecauses of airplane upsets to emphasize the prin-ciple of avoiding airplane upsets. Basic aerody-namic information indicates how and why large,swept-wing airplanes fly. That information pro-vides the foundation of knowledge necessary forrecovering an airplane that has been upset. Thissection highlights several issues associated withairplane upset recovery and presents basic recom-mended airplane-recovery techniques for pilots.There are infinite potential situations that pilotscan experience while flying an airplane. The tech-niques that are presented in this section are appli-cable for most situations.

2.6.1 Situation Awareness of anAirplane UpsetIt is important that the first actions for recoveringfrom an airplane upset be correct and timely.Guard against letting the recovery from one upsetlead to a different upset situation. Troubleshoot-ing the cause of the upset is secondary to initiat-ing the recovery. Regaining and then maintainingcontrol of the airplane is paramount.

It is necessary to use the primary flight instrumentsand airplane performance instruments when ana-lyzing the upset situation. While visual meteoro-logical conditions may allow the use of referencesoutside the airplane, it normally is difficult orimpossible to see the horizon. This is because inmost large commercial airplanes the field of viewis restricted. For example, the field of view from anairplane that exceeds 25-deg, nose-up attitude prob-ably is limited to a view of the sky. Conversely, thefield of view is restricted to the ground for a nose-down pitch attitude that exceeds 10 deg. In addi-tion, pilots must be prepared to analyze the situationduring darkness and when instrument meteoro-logical conditions (IMC) exist. Therefore, the At-titude Direction Indicator (ADI) is used as a primaryreference for recovery. Compare the ADI informa-tion with performance instrument indications be-fore initiating recovery. For a nose-low upset,

normally the airspeed is increasing, altitude isdecreasing, and the VSI indicates a descent. For anose-high upset, the airspeed normally is decreas-ing, altitude is increasing, and the VSI indicates aclimb. Cross-check other attitude sources, for ex-ample, the Standby Attitude Indicator and the PilotNot Flying (PNF) instruments.

Pitch attitude is determined from the ADI PitchReference Scales (sometimes referred to as PitchLadder Bars). Most modern airplanes also usecolors (blue for sky, brown for ground) or groundperspective lines to assist in determining whetherthe airplane pitch is above or below the horizon.Even in extreme attitudes, some portion of the skyor ground indications is usually present to assistthe pilot in analyzing the situation.

The Bank Indicator on the ADI should be used todetermine the airplane bank.

Situation analysis process:• Locate the Bank Indicator.• Determine pitch attitude.• Confirm attitude by reference to other

indicators.• Assess the energy.

Recovery techniques presented later in this sectioninclude the phrase, “Recognize and confirm thesituation.” This situation analysis process is usedto accomplish that technique.

2.6.2 Miscellaneous Issues AssociatedWith Upset RecoverySeveral issues associated with recovering from anupset have been identified by pilots who haveexperienced an airplane upset. In addition, obser-vation of pilots in a simulator training environ-ment has also revealed useful informationassociated with recovery.

2.6.2.1 Startle Factor

It has already been stated that airplane upsets donot occur very often and that there are multiplecauses for these unpredictable events. Therefore,pilots are usually surprised or startled when anupset occurs. There can be a tendency for pilots toreact before analyzing what is happening or tofixate on one indication and fail to properly diag-nose the situation. Proper and sufficient training isthe best solution for overcoming the startle factor.

SECTION 2

2.35

The pilot must overcome the surprise and quicklyshift into analysis of what the airplane is doing andthen implement the proper recovery. Gain controlof the airplane and then determine and eliminatethe cause of the upset.

2.6.2.2 Negative G Force

Airline pilots are normally uncomfortable withaggressively unloading the g forces on a largepassenger airplane. They habitually work hard atbeing very smooth with the controls and keeping apositive 1-g force to ensure flight attendant andpassenger comfort and safety. Therefore, theymust overcome this inhibition when faced withhaving to quickly and sometimes aggressivelyunload the airplane to less than 1 g by pushingdown elevator.

Note: It should not normally be necessary to obtainless than 0 g.

While flight simulators can replicate normal flightprofiles, most simulators cannot replicate sus-tained negative-g forces. Pilots must anticipate asignificantly different cockpit environment duringless-than-1-g situations. They may be floating upagainst the seat belts and shoulder harnesses. Itmay be difficult to reach or use rudder pedals ifthey are not properly adjusted. Unsecured itemssuch as flight kits, approach plates, or lunch traysmay be flying around the cockpit. These are thingsthat the pilot must be prepared for when recoveringfrom an upset that involves forces less than 1-gflight.

2.6.2.3 Use of Full Control Inputs

Flight control forces become less effective whenthe airplane is at or near its critical angle of attackor stall. Therefore, pilots must be prepared to usefull control authority, when necessary. The ten-dency is for pilots not to use full control authoritybecause they rarely are required to do this. Thishabit must be overcome when recovering fromsevere upsets.

2.6.2.4 Counter-Intuitive Factors

Pilots are routinely trained to recover fromapproach to stalls. The recovery usually requiresan increase in thrust and a relatively small reduc-tion in pitch attitude. Therefore, it may be counter-intuitive to use greater unloading control forces or

to reduce thrust when recovering from a high angleof attack, especially at lower altitudes. If the air-plane is stalled while already in a nose-downattitude, the pilot must still push the nose down inorder to reduce the angle of attack. Altitude cannotbe maintained and should be of secondaryimportance.

2.6.2.5 Previous Training inNonsimilar Airplanes

Aerodynamic principles do not change, but air-plane design creates different flight characteris-tics. Therefore, training and experience gained inone model or type of airplane may or may not betransferable to another. For example, the handlingcharacteristics of a fighter-type airplane cannot beassumed to be similar to those of a large, commer-cial, swept-wing airplane.

2.6.2.6 Potential Effects on Engines

Some extreme airplane upset situation may affectengine performance. Large angles of attack canreduce the flow of air into the engine and result inengine surges or compressor stalls. Additionally,large and rapid changes in sideslip angles cancreate excessive internal engine side loads, whichmay damage an engine.

Boeing Response

To

NTSB SafetyRecommendation

1

BOEING COMMERCIAL AIRPLANE GROUP FLIGHT OPERATIONS TECHNICAL BULLETIN

NUMBER:

707 717 727 737 747 02-1 B-717-02-09 02-1 02-2 13

747-400 757 767 777 DC-8 50 68 68 10 DC-8-02-01

DC-9 DC-10 MD-80 MD-90 MD-10 DC-9-02-01 DC-10-02-01 MD-80-02-01 MD-90-02-01 MD-10-02-01

MD-11 MD-11-02-01

DATE: May 13, 2002 These bulletins provide information which may prove useful in airline operations or airline training. This information will remain in effect depending on production changes, customer-originated modifications, and Service Bulletin incorporation. Information in these bulletins is supplied by the Boeing Company and may not be approved or endorsed by the FAA at the time of writing. Appropriate formal documentation will be revised, as necessary to reflect the information contained in these bulletins. For further information, contact Boeing Commercial Airplane Group, Chief Pilot, Training, Technical & Standards, P.O. Box 3707, Mail Stop 14-HA, Seattle, WA, USA 98124-2207, Phone (206) 655-1400, Fax (206) 655-3694, SITA: SEABO7X Station 627. SUBJECT: Use of rudder on transport category airplanes ATA NO: APPLIES TO: All 707, 717, 727, 737, 747, 757, 767, 777, DC-8, DC-9, DC-10, MD-80,

MD-90, MD-10 & MD-11 Background As part of the on-going accident investigation of American Airlines flight 587, an Airbus A300-600, the National Transportation Safety Board (NTSB) issued a Safety Recommendation letter on Feb. 8, 2002. The letter recommends that pilots be made aware that aggressive maneuvering using “sequential full opposite rudder inputs” can potentially lead to “structural loads that exceed those addressed by the requirements.” Airplanes are designed and tested based on certain assumptions on how pilots will use the rudder. These assumptions drive the FAA/JAA certification requirements and any additional Boeing design requirements. The net result of this approach is that there has been no catastrophic structural failure of a Boeing airplane due to a pilot control input in over 40 years of commercial operations involving more than 300 million flights. However, providing additional information to pilots about the characteristics of their aircraft in unusual circumstances may prove useful.

2

Rudder Maneuvering Considerations Jet transport airplanes, especially those with wing mounted engines, have large and powerful rudders. These powerful rudders are necessary to provide sufficient directional control of asymmetric thrust after an engine failure on takeoff and to provide suitable crosswind capability for both takeoff and landing. As the airplane flies faster, less rudder is needed for directional control and the available rudder deflection is therefore reduced. This reduction in rudder deflection is achieved through rudder limiting (discussed later in more detail). Maneuvering an airplane using the rudder will result in a yaw and roll response. The roll response is the result of sideslip. For example, if the pilot applies left rudder the nose will yaw left (Figure 1). This yawing response to the left will generate a sideslip (right wing forward). The resulting sideslip will cause the airplane to roll to the left (i.e., roll due to sideslip). The actual force on the vertical tail due to the rudder deflection tends to roll the airplane right, but as the sideslip moves the right wing forward, the net airplane roll rate is to the left. Figure 1 Rudder Induced Sideslip

It is difficult to perceive sideslip and few modern transport airplanes have true sideslip indicators. In older transport instrument panels the “ball” was an indicator of side force or acceleration, not sideslip angle. Some newer models have electronic flight displays with a slip/skid indication, which is still an indication of side force or acceleration; not sideslip. As the pilot applies more rudder, more sideslip is generated and a greater roll response will result. Large, abrupt rudder inputs can generate very large sideslip angles, much larger than encountered in a steady state sideslip (that which is reached with a slow

3

pedal input and held for a period of time). This is due to the dynamic response characteristics of the airplane (Figure 2). This “over yaw” can amplify the roll rate. It is important to use the rudder carefully so that unintended large sideslip angles and resulting roll rate do not develop. The amount of roll rate that is generated by using the rudder is typically proportional to the amount of sideslip, NOT the amount of rudder deflection. Figure 2 “Sideslip Response to Abrupt Steady Rudder Input”

Steady Pedal Input

Time

Side

slip

Ang

le

Over Yaw Steady State

Precise roll control using rudder is difficult and therefore not recommended. Because sideslip must build up to generate the roll, there is a time lag between the pilot making a rudder input and the pilot perceiving a roll rate. This lag has caused some pilots to be surprised by the abrupt roll onset and in some cases to interpret the rapid onset of roll as being caused by an outside element not related to their rudder pedal input. If the pilot reacts to this abrupt roll onset with another large rudder input in the opposite direction, large amplitude oscillations in roll and yaw can result. Cyclic rudder pedal inputs can result in very large amplitude sideslip oscillations (See Figure 3).

4

Figure 3 “Sideslip Response to Abrupt Cyclic Rudder Input”

Cyclic Pedal Input

Time

Side

slip

Ang

leOver Yaw Sequential Over Yaw

The sideslip angle that is momentarily reached with such “sequential over yaw” can be much larger than the over yaw associated with a single, abrupt rudder input (See Figure 2 & 3). When the rudder is reversed at this sequential over yaw/sideslip angle, the rudder induced fin force is added to the sideslip induced fin force (See Figure 4 & 5). The resulting structural loads can exceed the limit loads and possibly the ultimate loads, which can result in structural damage. Note: Limit loads are the maximum loads to be expected in service. Ultimate loads are the limit loads multiplied by prescribed factors of safety,

normally 1.5.

5

Figure 4 Rudder Induced Sideslip Forces Figure 5 Rapid Rudder Reversal Forces

Design Maneuvering Speed - Va A structural design maneuvering speed, Va, is defined for evaluating airplane structural design. At or below this speed, Boeing airplanes are capable of sustaining a single input to any set of control surfaces (elevators, ailerons, rudder(s)) to their maximum available authority (as limited by control surface limiters, blowdown, or control stops). These control surface inputs are to be in one axis (not in combination) and do not include control input reversal or oscillatory inputs. In addition, on Boeing airplanes at speeds above Va, full rudder input is evaluated out to the maximum operating air speed, Vmo/Mmo, and for some models, out to the design dive speed, Vd/Md (where Vd/Md is typically 30-60 knots/.05-.07 Mach higher than Vmo/Mmo). Therefore the pilot does not have to be concerned about how fast or how hard to push the rudder pedal in one direction, from zero to full available pedal deflection throughout the flight envelope (from a structural capability standpoint). The maneuver speed is provided in most FAA/JAA approved Flight Manuals in the Section 1 Limitations under Maximum Airspeed Limits, and is usually shown for the most critical gross weight. The more commonly known Turbulent Air Penetration Speed gives a rough approximation to maneuver speed. It should be pointed out, for reasons discussed in the next section, that many aircraft have structural capability beyond that required by the minimum structural design criteria of the FARs or JARs. Design maneuver speed should not be confused with the “minimum” or “recommended” maneuver speed supplied for each flap setting to be used in daily operation. These speeds are based on aerodynamic margins: margins to stick shaker, flap placard, and acceleration and deceleration capability during flap changes.

6

NTSB Recommendations

A. Explain to Flight Crews the structural certification requirements for the rudder and vertical stabilizer on transport category airplanes. Response: The FAA/JAA have three rudder maneuver structural load design requirements, that the rudder and vertical fin must meet in order to be certified. These requirements are met for all airspeeds up to the design maneuvering speed. In addition, newer airplane designs meet these requirements up to the design dive speed. Note: The following conditions are engineering design conditions that may be

physically impossible to fly.

1. At a zero sideslip condition, the airplane must be able to withstand a rapid rudder input to full rudder deflection. A Safety Factor of 1.5 is then applied. This means the structure must have at least a 50% safety margin over the maximum load generated by this maneuver.

2. Starting from a zero sideslip condition, the airplane must be able to withstand

a rapid rudder input to full deflection that is held at full deflection until the maximum sideslip angle (over yaw) is achieved. The airplane will exceed the maximum steady state sideslip due to the dynamic response characteristics of the airplane. A Safety Factor of 1.5 is then applied.

3. Starting from a maximum steady heading sideslip condition, the rudder is

rapidly returned to neutral while maintaining the sideslip angle. A Safety Factor of 1.5 is then applied.

During airplane certification, Boeing does not flight test these exact conditions, but gathers flight test data to validate structural loads analysis. This analysis, combined with ground structural load testing, ensures that the structure meets design requirements. The FAA/JAA impose structural load design requirements in addition to these rudder maneuver requirements. These include requirements for loads due to gusts, engine failure dynamics, and lateral control induced rolling conditions. Boeing airplane vertical fins can also sustain loads if the rudder is rapidly returned to neutral from the over yaw sideslip or the rudder is fully reversed from a full steady state sideslip.

B. Explain to Flight Crews that a full or nearly full rudder deflection in the opposite direction, or certain combinations of sideslip angle and opposite rudder deflection can result in potentially dangerous loads on the vertical stabilizer, even at speeds below the design maneuvering speed. Response: Boeing airplanes are designed to withstand the structural loads generated by a full rudder input out to the airplane’s maximum operating airspeed, Vmo/Mmo. Some Boeing airplanes meet these requirements out to the design dive speed. This means the structure has at least a 50% safety margin over the maximum load

7

generated by this kind of maneuver. As previously mentioned, Boeing airplane vertical fins can also sustain loads if the rudder is rapidly returned to neutral from the over yaw sideslip or the rudder is fully reversed from a full steady state sideslip. Boeing airplanes are not designed to a requirement of full authority rudder reversals from an “over yaw” condition. Sequential full or nearly full authority rudder reversals may not be within the structural design limits of the airplane, even if the airspeed is below the design maneuvering speed. There are no Boeing Procedures that require this type of pilot input. It should also be pointed out that excessive structural loads may be generated in other areas of the airplane, such as engine struts, from this type of control input. In addition, large sideslip angles may cause engine surging at high power settings.

It is important to note that use of full rudder for control of engine failures and crosswind takeoffs and landings is well within the structural capability of the airplane.

C. Explain to Flight Crews that on some aircraft, as speed increases, the maximum

available rudder deflection can be obtained with comparatively light pedal forces and small pedal deflections. Response: Implementation of the rudder limiting function and associated forces vary from model to model. The force a pilot feels when pushing on the rudder pedals of a Boeing airplane is analogous to that of a force generated by a spring. The more the pedal is displaced the greater the required force. All modern transport airplanes limit rudder deflection as airspeed increases. Engine out takeoff and crosswind landing requirements define the maximum rudder deflection (authority). As the airplane flies faster, less deflection is needed and rudder authority is therefore reduced. Some Boeing models (747, 757, 767, & 777) have rudder limiters that reduce the rudder authority by changing the gearing between the rudder and the rudder pedals. As the airplane speeds up, the pilot must continue to fully deflect the rudder pedal to command full available rudder, even though the maximum available rudder deflection has been reduced. This means the pilot will have to apply the same force to the rudder pedal to achieve maximum available rudder deflection throughout the flight envelope. On other Boeing models (707, 717, 727, 737, DC-8, DC-9, MD-80, MD-90, DC-10 & MD-11), as the airplane speeds up, the rudder authority is limited, but the gearing between the rudder and the rudder pedal does not change. Since rudder authority is limited, rudder pedal travel is also limited; i.e., full rudder pedal deflection is not required to get full available rudder deflection. Rudder pedal force is a function of rudder pedal deflection, so less force will be required to achieve maximum available rudder deflection as airspeed increases Table 1 contains approximate values for rudder pedal force, rudder pedal travel and rudder deflection for the models listed. Three flight conditions (airspeeds) are presented: V1 (135 knots), 250 knots, and Mmo at FL390.

8

Table 1 Rudder Deflection and Force Required

V1 (135) 250 kts FL390 MMo

Pedal Force (lbs)

Pedal Travel

(in)

Rudder Deflection

(deg)

Pedal Force (lbs)

Pedal Travel

(in)

Rudder Deflection

(deg)

Pedal Force (lbs)

Pedal Travel

(in)

Rudder Deflection

(deg) 747 80 4 30 80 4 12 80 4 8 757 80 4 26 80 4 6 80 4 5 767 80 3.6 26 80 3.6 8 80 3.6 7

777 60 2.9 27 60 2.9 9 60 2.9 6

707 70 2.3 24 100 1.3 9 100 1.1 7

717 75 3.3 29 65 1.6 13 40 0.5 4

727 80 3 18 50 1.3 7 45 1.3 6

737 70 2.8 18 50 1.0 4 50 1.0 4

DC8 85 3.6 32 65 1.5 13 60 1.0 8

DC9 75 2.6 22 60 1.1 8 30 0.4 3

MD 80

75 2.6 22 60 1.1 8 30 0.4 3

MD 90

75 3.3 29 65 1.6 13 40 0.5 4

DC 10

80 3.8 23 65 2 14 55 1.5 9

MD 11

80 3.8 23 65 2.2 15 60 1.7 11

Airplanes do vary on the amount of rudder pedal force and displacement required to achieve maximum available rudder as airspeed changes. It is important that pilots understand their airplane’s feel and response characteristics to flight control inputs. By understanding and becoming familiar with the airplane’s characteristics, pilots will learn to apply the appropriate control input in response to various flight situations.

9

D. Carefully review all existing and proposed guidance and training provided to pilots of transport-category airplanes concerning special maneuvers intended to address unusual or emergency situations and, if necessary, require modifications to ensure that flight crews are not trained to use the rudder in a way that could result in dangerous combinations of sideslip angle and rudder position or other flight parameters.

Response: Boeing agrees that additional and more comprehensive dissemination of information to flight crews about aircraft characteristics and capabilities may prove useful. For example, Boeing strongly supports industry efforts to improve training of airline flight crew in:

• Techniques of large aircraft upset recovery • Appropriate response to wake vortex encounters • Consequences of pilot initiated security related in-flight maneuvers.

To aid in pilot education, a significant amount of material is currently available and should be incorporated and stressed in pilot training programs. For example, Boeing Flight Crew Training Manuals and Flight Crew Operating Manuals contain material on upset recovery guidance that includes guidance on the proper use of the rudder. The Quick Reference Handbook (QRH), in the Non-Normal Maneuvers section under Upset Recovery contains the Warning: “Excessive use of pitch trim or rudder may aggravate an upset situation or may result in loss of control and/or high structural loads.” In addition, Boeing has published related information such as the article “Aerodynamic Principles of Large- Airplane Upsets” in its AERO magazine (Vol. 3 1998) and the Airplane Upset Recovery Training Aid in which similar guidance was provided in a much more detailed format. Boeing supports efforts that will assure that this information and other similar materials reliably reach pilots in line operations. Additionally, there may be misconceptions among transport pilots about the use of flight controls, how aircraft may be maneuvered, and what are the structural load capabilities of transports. These misconceptions may be due to previous experience with other aircraft classes or configurations (e.g., tactical military aircraft, small General Aviation {GA} aircraft). Such misconceptions could lead transport pilots to attempt maneuvers in unusual situations that could make the situation worse and introduce excessive risk. The issue is further compounded by the limitations in simulator fidelity that may cause pilots to assume some maneuvers are feasible and repeatable. Boeing recommends that:

• Transport pilots should be made aware that certain prior experience or training in military, GA, or other non-transport aircraft that emphasizes use of rudder input as a means to maneuver in roll typically does not apply to transport aircraft or operations.

10

• Transport pilots should be made aware that certain prior experience or training in military, GA, or other non-transport aircraft types emphasizing the acceptability of unrestricted dynamic control application typically does not apply to transport aircraft or operations. Excessive structural loads can be achieved if the aircraft is maneuvered significantly different than what is recommended by the manufacturer or the operator’s training program.

Finally, as background information, crews should “optionally” be able to learn more about their aircraft, such as how certain regulatory certification practices are accomplished. This could help them better understand what their aircraft have been tested for, the maneuvers their aircraft have been shown to be capable of safely doing, and conditions that have not specifically been tested. For example, a manufacturer is required to demonstrate full stall and stall recovery characteristics. The FAA assesses whether the characteristics during a full stall are acceptable and that the recovery does not require any unusual pilot technique. Note that these stalls are not done in large dynamic yaw rate or sideslip conditions. Boeing airplanes have demonstrated entry and recovery from full stalls without the need for rudder. Boeing strongly recommends that the rudder not be used in a stall recovery, and that stall recovery should be accomplished before proceeding with any unusual attitude recovery. Once the stall recovery is complete, the ailerons/spoilers should provide adequate rolling moment for unusual attitude recovery. Unless a transport airplane has suffered significant loss of capability due to system or structural failure (such as a loss of a flap or thrust reverser deployment), rudder input is generally not required.

In simple pilot terms, if you are in a stall, don’t use the rudder; if you are not in a stall, you don’t need the rudder. The rudder in a large transport airplane is typically used for trim, engine failure, and crosswind takeoff and landing. Only under an extreme condition, such as loss of a flap, mid air collision, or where an airplane has pitched to a very high pitch attitude and a pushover or thrust change has already been unsuccessful, should careful rudder input in the direction of the desired roll be considered to induce a rolling maneuver to start the nose down or provide the desired bank angle. A rudder input is never the preferred initial response for events such as a wake vortex encounter, windshear encounter, or to reduce bank angle preceding an imminent stall recovery. Finally, following the events of September 11, there has been much discussion about aggressively maneuvering the airplane to thwart a hijacking attempt. The Boeing recommendation in this situation has been to rely on maneuvers that do not apply inputs to the rudder. The issues discussed in this bulletin have shown the risks associated with large rudder inputs. The use of ailerons and elevators in this situation has limitations as well. Elevators and ailerons are not designed for abrupt reversals from a fully displaced position. In all cases the manufacturer’s specific recommendations for aggressive maneuvering should be followed. Random unplanned maneuvers outside the manufacturer’s recommendations can lead to loss of control and/or structural damage.

11

Summary

• There has been no catastrophic structural failure of a Boeing airplane due to a

pilot control input in over 40 years of commercial operations involving more than 300 million flights.

• Jet transport airplanes have large and powerful rudders. • The use of full rudder for control of engine failures and crosswind takeoffs and

landings is well within the structural capability of the airplane. • As the airplane flies faster, less rudder authority is required. Implementation of

the rudder limiting function varies from model to model.

• Airplanes are designed and tested based on certain assumptions about how pilots will use the rudder. These assumptions drive the FAA/JAA certification requirements and any additional Boeing design requirements.

• The pilot should be aware that the airplane has been designed with the structural

capability to accommodate a rapid and immediate rudder pedal input when going in one direction from zero input to full.

• It is important to use the rudder in a manner that avoids unintended large sideslip

angles and resulting excessive roll rates. The amount of roll rate that is generated by using the rudder is proportional to the amount of sideslip, NOT the amount of rudder input.

• If the pilot reacts to an abrupt roll onset with a large rudder input in the opposite

direction, the pilot can induce large amplitude oscillations. These large amplitude oscillations can generate loads that exceed the limit loads and possibly the ultimate loads, which could result in structural damage.

• A full or nearly full authority rudder reversal as the airplane reaches an “over

yaw” sideslip angle may be beyond the structural design limits of the airplane. There are no Boeing flight crew procedures that would require this type of rudder input.

12

Attachment One

COMMONLY ASKED QUESTIONS REGARDING RUDDER USEAGE 1. The NTSB recommendation mentions that any new rudder training should

not compromise the substance or effectiveness of existing training regarding proper rudder use (i.e. engine out during takeoff, crosswind landings). Please provide Boeing comments about this.

A- Service history and previous investigations demonstrate that pilots must be willing to use full available control authority in certain specific situations such as engine out during takeoff. We agree with the NTSB that any new guidance that is developed must not undermine this training.

2. During an engine failure situation, would an initial input of rudder in the

wrong direction followed by a rapid full input in the opposite direction cause structural problems with the rudder or vertical stabilizer?

A- No, such a maneuver does not result in excessive loads being produced.

3. Some non-normal procedures call for using maximum force to overcome

jammed controls. If I have a jam in one direction and do the procedure and the jam frees itself will I overstress the airplane?

A- If the rudder is jammed off neutral, the airplane will establish itself in a steady state sideslip. The removal of the jam condition will not overstress the airplane.

4. At what point are the stresses on the tail at the maximum if I put in full

rudder? Right before the limiter starts reducing the travel? Maximum speed?

A- The point of maximum stress will depend on the airplane type, configuration, and specific maneuver. However, from a zero sideslip condition the maximum available rudder can be applied in one direction out to the maximum operating speed, Vmo/Mmo, and for some models, out to the design dive speed, Vd/Md.

5. At high angles of attack, beyond stick shaker, the roll effectiveness of the

ailerons and spoilers is decreased. On some airplanes this is more pronounced than others. Should I use rudder, up to full authority, to assist in maintaining wings level, especially if I encounter a back and forth rolling motion?

13

A- If the airplane is stalled the use of rudder for roll control is not recommended. Precise roll control using rudder is difficult, and the use of rudder could aggravate the situation. If after applying full nose down elevator and reducing thrust, a pitch down response does not occur, apply a small amount of rudder to initiate a roll and resultant pitch down. As roll control is regained, the rudder should be centered.

6. During a wind shear recovery, large control wheel inputs can cause the

spoilers on one wing to deflect, with a resultant reduction in lift and increase in drag. Should I keep the control wheel level and use rudder to control roll?

A- In wind shear recovery the use of rudder is not recommended. Precise roll control using rudder is difficult, and the use of rudder could aggravate the situation. Additionally, from a human factors standpoint, it is not reasonable to expect pilots to maintain a level control wheel in these conditions as a reaction to roll upsets. Lift loss and drag produced from spoiler deflection during upset recovery is momentary.

7. In the 747 with an engine failure at V1 I am taught the technique of full

rudder then take ½ of it out and hold. Does that put undue stress on the tail?

A- This technique for rudder movement does not put undue stress on the tail structure.

8. If my aircraft is upset and in a 90-degree bank and the ailerons appear to be

ineffective, should I smoothly put in rudder or can I aggressively put it in? What should I do when it rapidly reverses the roll?

A- The first action to take is to unload the airplane to the point of being “light in the seat” to improve roll capability. If this does not improve roll control then the smooth application of small amounts of coordinated rudder in the direction of the desired roll can assist in rolling the airplane. Aggressive rudder application could cause a rapid roll. If this occurs, the rudder should be moved to neutral and aileron control used to complete the recovery.

9. What pilot action should I take to recover when I encounter wake

turbulence?

A- Normal piloting actions for roll control are sufficient for large commercial jet transports. If a roll off does occur, the normal use of ailerons and spoilers should be sufficient to recover. The use of rudder is not recommended. The induced roll from the vortex will be more severe for short span airplanes (relative to the aircraft that generated the vortex) but the recovery procedures are the same. Crews should perform the upset recovery procedures if bank angles of greater than 45 degrees are encountered.

14

10. Does Boeing have pre-planned upset recovery scenarios that can be plugged into the simulator and activated by the instructor?

A- Boeing does not have pre-planned system failure upset recovery scenarios. Simulator manufacturers have assisted some carriers in activating such scenarios. Boeing does provide Simulator Training Exercise in the Airplane Upset Recovery Aid. These exercises demonstrate techniques for recovering from an upset regardless of the cause. The training recommended in the Training Aid has been researched and test flown to ensure that sideslip and angle of attack limits are not exceeded. Additional simulator envelope information is provided in the Appendix to the Training Aid. Therefore, simulator action correctly mimics real airplane performance. Simulators flown outside the limits of valid data can present misleading airplane response. Airlines should use caution when activating pre-loaded scenarios such that data limits are not exceeded and that poor habit patterns are not instilled that will have negative consequences.

11. How much force are Boeing tails designed to withstand?

A- The tail structures of Boeing airplanes are designed to withstand at least 1.5 times the maximum forces airplanes are expected to encounter in service.

12. Has the vertical tail of a Boeing commercial jet ever failed in flight?

A- No vertical tail has ever broken off a Boeing commercial jet in revenue service due to rudder movements. There was a 747 accident in 1985 in which significant damage occurred to the vertical tail when the aft pressure bulkhead failed and the airplane rapidly decompressed. Additionally, structural damage has occurred due to lighting strikes, midair collisions, and engine failures. Damage has also occurred in flight test but the damage was not due to use of controls.

13. What kind of tests do you do to ensure the vertical tail is strong enough?

A- There are numerous tests that directly verify structural integrity, or support analytical methods:

• Element testing for mechanical properties (e.g., strength, stiffness, uniformity) of raw materials, fasteners, bolted-joints, etc. This includes the effects of environment and manufacturing flaws.

• Subcomponent tests to validate concepts, to verify analytical methods, provide substantiating data for material design values, demonstrate repairs, and show compliance with strength requirements in configured structure. These tests include ribs, spars, skin panels, joints and fittings.

15

• The full-scale airplane, with fin attached, is tested for static strength to prove ultimate load capability. A separate full-scale airplane with fin attached is tested under simulated service loads for 3 lifetimes to show durability and lack of widespread fatigue damage. A separate full-scale horizontal stabilizer is tested for static strength and fatigue also.

• Boeing then flight tests the airplane to gather flight test data to validate

structural loads analysis. This analysis, combined with ground structural load testing, ensures that the structure meets design requirements.

14. Which Boeing models have composite vertical tails?

A- The 777 has a vertical tail made of composites.

15. Where else has Boeing used composites in its airplanes?

A- Composite materials were used on secondary structure on the 727 (fairing, radome, trailing edges). As technology advanced, more composites were used on new airplane models such as the 737, 757, 767 and 777. Composites also were used on the MD-80, MD-90, MD-11 and 717. Many other components on the 777 contain composite materials. Examples include fairings, floor beams, engine nacelles, rudder and elevator, movable and fixed wing trailing edge surfaces, and gear doors. The 777 is similar to other Boeing models in that elevators and rudders are made of composite materials (the skins, ribs and spars). There are metal ribs and fittings that attach the rudder/elevator to the stabilizer structures.

16. Are composite tails as strong as metal tails?

A- Yes. If one were to go through the design process for a metal or composite tail for the same airplane, then the same requirements would be applied. Similar engineering activities would occur (i.e., aerodynamic analysis, external loads, structural design, stress analysis, material qualification, manufacturing verification, testing, validation, maintenance & inspection planning, certification, in-service monitoring, etc.).

Airbus Response

To

NTSB SafetyRecommendation

Flight Simulator

Aero Model

Information

App. 3-D.1

APPENDIX

3-D

Flight Simulator Information

3-DGeneral Information

The ability of the simulators in existence today toadequately replicate the maneuvers being pro-posed for airplane upset recovery training is animportant consideration. Concerns raised aboutsimulators during the creation of the AirplaneUpset Recovery Training Aid include the adequacyof the hardware, the equations of motion, and theaerodynamic modeling to provide realistic cues tothe flight crew during training at unusual attitudes.

It is possible that some simulators in existencetoday may have flight instruments, visual systemsor other hardware that will not replicate the fullsix-degree-of-freedom movement of the airplanethat may be required during unusual attitude train-ing. It is important that the capabilities of eachsimulator be evaluated before attempting airplaneupset training and that simulator hardware andsoftware be confirmed as compatible with thetraining proposed.

Properly implemented equations of motion inmodern simulators are generally valid through thefull six-degree-of-freedom range of pitch, roll, andyaw angles. However, it is possible that someexisting simulators may have equations of motionthat have unacceptable singularities at 90, 180,270, or 360 deg of roll or pitch angle. Each simu-lator to be used for airplane upset training must beconfirmed to use equations of motion and mathmodels (and associated data tables) that are validfor the full range of maneuvers required. Thisconfirmation may require coordination with theairplane and simulator manufacturer.

Operators must also understand that simulatorscannot fully replicate all flight characteristics. Forexample, motion systems cannot replicate sus-tained linear and rotational accelerations. This istrue of pitch, roll, and yaw accelerations, andlongitudinal and side accelerations, as well asnormal load factor, “g’s.” This means that a pilotcannot rely on all sensory feedback that would beavailable in an actual airplane. However, a prop-erly programmed simulator should provide accu-rate control force feedback and the motion systemshould provide airframe buffet consistent with the

aerodynamic characteristics of the airplane whichcould result from control input during certainrecovery situations.

The importance of providing feedback to a pilotwhen control inputs would have exceeded air-frame, physiological, or simulator model limitsmust be recognized and addressed. Some simula-tor operators have effectively used a simulator’s“crash” mode to indicate limits have been ex-ceeded. Others have chosen to turn the visualsystem red when given parameters have been ex-ceeded. Simulator operators should work closelywith training departments in selecting the mostproductive feedback method when selected pa-rameters are exceeded.

The simulation typically is updated and validatedby the airplane manufacturer using flight dataacquired during the flight test program. Before asimulator is approved for any crew training, itmust be evaluated and qualified by a nationalregulatory authority. This process includes a quan-titative comparison of simulation results to actualflight data for certain test conditions such as thosespecified in the ICAO Manual of Criteria for theQualification of Flight Simulators. These flightconditions represent airplane operation within thenormal operating envelope.

The simulation may be extended to represent re-gions outside the typical operating envelope usingwind tunnel data or other predictive methods.However, flight data are not typically available forconditions where flight testing would be veryhazardous. From an aerodynamic standpoint, theregimes of flight that are usually not fully vali-dated with flight data are the stall region and theregion of high angle of attack with high sideslipangle where there may be separated airflow overthe wing or empennage surfaces. While numerousapproaches to stall or stalls are flown on eachmodel (available test data are normally matchedon the simulator), the flight controls are not fullyexercised during an approach to stall or during afull stall, because of safety concerns. Also, roll andyaw rates and sideslip angle are carefully con-trolled during stall maneuvers to be near zero;therefore, validation of derivatives involving these

App. 3-D.2

APPENDIX

3-D

terms in the stall region is not possible. Trainingmaneuvers in this regime of flight must be care-fully tailored to ensure that the combination ofangle of attack and sideslip angle reached duringthe maneuver does not exceed the range of vali-dated data or analytical/extrapolated data sup-ported by the airplane manufacturer.

Values of pitch, roll, and heading angles, however,do not directly affect the aerodynamic characteris-tics of the airplane or the validity of simulatortraining as long as angle of attack and sideslipangles do not exceed values supported by theairplane manufacturer. For example, the aerody-namic characteristics of the upset experiencedduring a 360-deg roll maneuver will be correctlyreplicated if the maneuver is conducted withoutexceeding the valid range of angle of attack andsideslip.

Simulator Alpha-Beta Data Plots

The aerodynamic model for each simulation maybe divided into regions of various “confidencelevels,” depending on the degree of flight valida-tion or source of predictive methods if supportedby the airplane manufacturer, correctly imple-mented by the simulator manufacturer and accu-rately supported and maintained on an individualsimulator. These confidence levels may be classi-fied into three general areas:

1. High: Validated by flight test data for avariety of tests and flight conditions.

2. Medium:Based on reliable predictivemethods.

3. Low: Extrapolated.

The flaps up data represent the maximums achievedat low speeds flaps up and do not imply that thesevalues have been achieved at or near cruise speeds.For flaps down, the maximums were generallyachieved at landing flaps, but are considered validfor the flaps down speed envelope.

App. 3-D.3

APPENDIX

3-D

A300/A310 Flaps Up Alpha/Beta Envelope

-10

-40 -30 -20 -10 0 10 20 30 400

10

20

30

40 Flight validatedWind tunnel/analyticalExtrapolated for simulator

Sideslip (deg)

Win

g an

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(de

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Flight validatedWind tunnel/analyticalExtrapolated for simulator

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A300/A310 Flaps Extended Alpha/Beta Envelope

App. 3-D.4

APPENDIX

3-D


-10

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727 Alpha/Beta Envelope

App. 3-D.5

APPENDIX

3-D


-40 -30 -20 -10 0 10 20 30 400

10

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Sideslip (deg)

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(de

g)737 Flaps Up Alpha/Beta Envelope

737 Flaps Extended Alpha/Beta Envelope

App. 3-D.6

APPENDIX

3-D

747 Flaps Up Alpha/Beta Envelope



Sideslip (deg)

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of a

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(de

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-40 -30 -20 -10 0 10 20 30 400

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App. 3-D.7

APPENDIX

3-D




-40 -30 -20 -10 0 10 20 30 400

10

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Sideslip (deg)

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App. 3-D.8

APPENDIX

3-D




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Sideslip (deg)

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App. 3-D.9

APPENDIX

3-D




Sideslip (deg)

Win

g an

gle

of a

ttack

(de

g)


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App. 3-D.10

APPENDIX

3-D

MD-90 Flaps Up Alpha/Beta Envelope

MD-90 Alpha/Beta Envelope Flaps Deflected


-10

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App. 3-D.11

APPENDIX

3-D

MD-11 Flaps Up Alpha/Beta Envelope

MD-11 Alpha/Beta Envelope Flaps Deflected


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