Aircraft Instrument Fudamentals

AIRCRAFT INSTRUMENT FUDAMENTALS

AERO 5386CLASS 3325

Learning Outcomes

State the ICAO instrumentation requirements & describe instrumentation elements, mechanisms, error sources and temperature compensationDescribe the lighting of panel-mounted instrumentsDescribe concepts and terms relating to the operation of aircraft instrumentation DC synchronous systemsDescribe the operation of engine indicating systems Describe the operation of temperature indicating systemsDescribe the operation of fuel quantity and flow systemsDescribe the principle of operation of pitot static flight instrumentsDescribe and explain the operation & construction of direct reading magnetic compasses

Learning Outcomes ContdDescribe and explain the operation of flight instruments incorporating gyroscopes & define related termsDescribe and explain using words & diagrams, the operation gyro-magnetic compass systemsDescribe and explain the operation of a flight director system to block diagram levelDescribe & explain the operation of accelerometers, fatigue meters & flight data recorders

Learning Outcome 1 Assessment CriteriaState the ICAO instrumentation requirements & describe instrumentation elements, mechanisms, error sources and temperature compensation

State the requirements for instrumentations IAW the International Civil Aviation Organisation (ICAO)

Describe the following elements of an instrument system a. detecting b. measuring c. coupling d. indicating

Describe how the following components function in instrument systems a. levers b. rods c. gears

Learning Outcome 1 Assessment CriteriaContdDescribe the function of hairsprings & jewelled bearings

Define the following terms : a. range error b. position error c. hysteresis error d. random error

Describe the following methods of temperature compensation in instrument mechanism a. bi-metal strip b. thermo- resistance c. thermo- magnetic shunt

Learning Outcome 2 Assessment CriteriaDescribe the lighting of panel-mounted instruments

Describe the types of instruments lighting, including: Flood lights Pillar lights bridge lighting internal (edge) lighting

List the types of control panel lighting, including: integrated electroluminescent

Learning Outcome 3 Assessment Criteria

Describe concepts & terms relating to the operation of aircraft instrumentation DC synchronous system

Describe the purpose of DC synchronous system

Describe the principle of operation DC synchronous system

Describe the purpose of AC synchronous system

Describe the principle of operation AC synchronous system

Learning Outcome 3 Assessment CriteriaContd5. State the purpose & identify the circuit symbols of the followingTorque synchro systemTorque synchro transmitter (TX)Torque synchro receiver (TR) Control synchro systemControl synchro transmitter (CX)Control synchro transformer (CT)Torque synchro differential transmitter (TDX)Control synchro differential transmitter (CDX)E & I bar sensors

Learning Outcome 4 Assessment Criteria

Describe the operation of engine Indicating systems

4.1 Describe the operation of DC speed measuring systems 4.2Describe the operation of AC speed measuring systems4.3Describe the operation of pulsed speed measuring systems4.4Describe the operation of oil pressure indicating systems4.5Describe the operation of manifold pressure indicating systems4.6Describe the operation of engine pressure ratio gauges4.7Describe the operation of engine vibration monitoring systems4.8Describe the operation of torque meters

Learning Outcome 5 Assessment Criteria Describe the operation of temperature Indicating system

5.1Define Static Air Temperature (SAT), Ram Air Temperature (RAT) and Total Air Temperature (TAT)5.2Describe the operation of Wheatstone Bridge based temperature indicating systems5.3 Describe the operation of Thermocouple temperature indicating systems 5.4 List the various combinations of Thermocouple materials used and state their operating parameters5.5. Describe the operation of the cold junction compensation for thermocouple leads and probes5.6 Describe the construction and operation of radiometer type temperature indicating systems 5.7Describe the construction and operation of radiation pyrometer type temperature indicating systems

Learning Outcome 6 Assessment CriteriaDescribe the operation of fuel quantity and flow systems

6.1 State the difference between 'Volumetric' and 'Mass' fuel indicating systems6.2 State the effects of temperature and density on fuel quantity indicating systems

6.3 List the types of DC volumetric indicating systems6.4 Describe the operation of mass fuel quantity indicating systems6.5 State the requirements of fuel flow measuring systems6.6 Describe the operation of fuel flow measuring systems

Learning Outcome 7 Assessment CriteriaDescribe the principle operation of of pitot static flight instrumenets

7.1 State the layers of the atmosphere and describe the effects of altitude on pressure and temperature

7.2 Describe the effects of humidity, temperature and pressure on air density

7.3 Describe the characteristics of the International Standard Atmosphere (ISA) and the methods of measuring atmospheric pressure

7.4 In terms of the ISA define:lapse ratedensitytemperaturepressure

7.5 Describe the construction, operation and Junction of the following sensing devices:Bellows (absolute and differential)Bourdon tubesCapsules (absolute and differential)Diaphragms

Learning Outcome 7 Assessment Criteria ContdDescribe the principle operation of of pitot static flight instruments7.6 describe the construction and operation of pilot, pilot/static probes and static vents (primary and alternate)7.7 State the heating requirements for pitot, pitot/static probes and the methods of indication7.8 Explain position error and its effect on pitot static instruments7.9 Describe the layout of a typical pitot static aircraft system Carry out a pitot static leak test in accordance with (IAW) the7.10 relevant orders on both VFR and IFR aircraft7.11 Describe the construction and operation of an altimeter and explain the effects of temperature and atmospheric pressure changes on their indication7.12 Describe the different methods of presentation of altimeter indications7.13 Define the terms: QFE QNE QNH

Learning Outcome 7 Assessment Criteria ContdDescribe the principle operation of of pitot static flight instruments7.14 Describe the methods of adjustment applied to an altimeter to allow for the application of the settings of QFE, QNE, QNH7.15 Define the term Flight Level and describe the effect on altimeter reading when 1013.2mb is set on the barometric scale7.16 Describe the serviceability tests which can be applied to the altimeter system IAW relevant orders and instructions7.17 Describe the construction and operation of the vertical speed indicator and the instantaneous vertical speed indicator7.18 Define the following terms:Indicated, calibrated and true airspeedMach number and critical mach numberMaximum mach operating (MMO)Sonic, subsonic, transonic and supersonic speedsspeed of soundVelocity maximum operating (VMO

Learning Outcome 7 Assessment Criteria ContdDescribe the principle operation of of pitot static flight instruments7.19 Describe the construction and operation of:airspeed switches airspeed indicators Mach airspeed indicators Mach metersMaximum allowable airspeed indicators

7.20 Describe the construction and operation of a typical altitude alerting and reporting system including encoding altimeters

7.21 State the purpose of a central air data computer system (CADC)7.22 State the purpose of a:stall warning systemangle of attach system (Alpha Poles)

Learning Outcome 8 Assessment Criteria Describe the construction and operation of Direct reading & Magnetic compasses8.1 Define the following terms in relation to terrestrial magnetism: aclinic line or magnetic equator agonic line angle of dip deviation isoclinic line isogonal line magnetic meridian magnetic and geographic polesvariation or declination.8.2 describe the construction and operation of a direct reading magnetic compass

8.3 describe the following inherent errors or deficiencies in direct reading compasses and the methods used to overcome them:Soft iron and hard iron magnetismA, B, C errorsAcceleration and turning errors

Learning Outcome 9 Assessment Criteria Describe and explain the operation of flight instruments incorporating gyroscopes & defined related areas9.1 Describe the operation of a gyroscope when used as a reference for displacement and rate

9.2 Describe the limitations of a displacement gyroscope

9.3 Describe the effect of rotor speed change on the output of a rate gyroscope

9.4 Define the term tied gyroscope

9.5 Describe the errors that affect a spinning mass gyroscope, including: real drift apparent drift transport rate

Learning Outcome 9 Assessment Criteria Contd Describe and explain the operation of flight instruments incorporating gyroscopes & defined related areas9.6 Describe the method of correction for the following errors: real drift apparent drifttransport rate

9.7 Describe the operation of a displacement gyroscope when used in artificial horizons and directional gyros

9.8 State the purpose of erection systems used on gyroscopes anddescribe their operation in artificial horizons and directional gyros

9.9 State the purpose and describe the principle of operation of a turn and slip indicator

Learning Outcome 10 Assessment Criteria Describe and explain using words and diagrams, the operation of gyro-magnetic compass systems

10.1 Sketch the block diagram of a gyro-magnetic compass system

10.2 List the advantages of a gyro-magnetic compass system over direct reading compasses

10.3 Describe the principle of operation of flux detector valves

10.4 Describe the two modes of gyro-magnetic compass system operation

10.5 Describe the principle of operation of gyro-magnetic compass systems

Learning Outcome 11 Assessment Criteria

Describe and explain the operation of a flight director system (FDS) to block diagram level

11.1 State the purpose of an FDS

11.2 List the components of a typical FDS

11.3 State the purpose of the controls and displays on:

horizontal situation indicators (HSIs) attitude direction indicators (ADIs)

11.4 Describe the operation of an FDS to block diagram level

Learning Outcome 11 Assessment CriteriaDescribe and explain the operation of accelerometers, fatigue meters and flight data recorders.

12.1 State the purpose and describe the principle of operation of:

accelerometers fatigue meters flight data recorders

IntroductionThe complexity of modern aircraft and all allied equipment and the nature of the environmental conditions under which they must operate, require conformity of design, development and subsequent operation with established requirements and standards.The international operation of civil aircraft necessitates international recognition that aircraft do, in fact, comply with their respective national airworthiness requirements. As a result, international standards of airworthiness are also laid down by the International Civil Aviation Organisation (ICAO). These standards do not replace national regulations, but serve to define the complete minimum international basis for the recognition by countries of airworthiness certification.

1.1 RequirementsLocation, Visibility and Grouping of Instruments1. All instruments shall be located so that they can be read easily by the appropriate member of the flight crew.2. When illumination of instruments is provided, there shall be sufficient illumination to make them easily readable and discernible by night. Instrument lights shall be installed in such a manner that the pilot's eyes- are shielded from their direct rays and that no objectionable reflections are visible to him.3. Flight, navigation and power plant instruments for use by a pilot shall be plainly visible to him from his station with the minimum practicable deviation from his normal position and line of vision when he is looking out- and forward along the flight path of the aircraft.4. All flight instruments shall be grouped on the instrument panel and, as far as practicable, symmetrically disposed about the vertical plane of the pilot's forward vision.5. All the required power plant instruments shall be conveniently grouped on instrument panels and in such a manner that they may be readily seen by the appropriate crew member.6. In multi-engine aircraft, identical power plant instruments for the several engines shall be located so as to prevent any misleading impression as to the engines to which they relate.

Instrument PanelsThe vibration characteristics of instrument panels shall be such as not to impair seriously the accuracy of the instruments or to damage them. The minimum acceptable vibration insulation characteristics are established by standards formulated by the appropriate national organisation.

1.2 Instruments to be Installed Flight and Navigation Instruments

1. Altimeter adjustable for changes in barometric pressure.2. Airspeed indicator.3. Vertical speed indicator.4. Gyroscopic bank-and-pitch attitude indicator.5. Gyroscopic rate-of-turn indicator (with bank indicator).6. Gyroscopic direction indicator.7. Magnetic compass.8. Outside air temperature indicator.9. clock.

Pitot-static System

Instruments 1, 2 and 3 mentioned previously form part of an aircraft's pitot-static system, which must also conform to certain requirements. These are summarised as follows:

the system shall be airtight, except for the vents to atmosphere and shall be arranged so that the accuracy of the instruments cannot be seriously affected by the aircraft's speed, attitude or configuration; by moisture; or other foreign matter;

2. the system shall be provided with a heated pitot-pressure probe to prevent malfunctioning due to icing;

3. sufficient moisture traps shall be installed to ensure positive drainage throughout the whole of the system;

4. in aircraft in which an alternate or emergency system is to be installed, the system must be as reliable as the primary one and any selector valve must be clearly marked to indicate which system is in use;

5. pipelines shall be of such an internal diameter that pressure lag and possibility of moisture blockage is kept to an acceptable minimum;

6. where static vents are used, to obviate yawing errors, they shall be situated on opposite sides of the aircraft and connected together as one system. Where duplicate systems are prescribed, a second similar system shall be providedPitot-static System Contd

Gyroscopic Instruments

Gyroscopic instruments may be of the vacuum-operated or electrically operated type, but in all cases, the instruments shall be provided with two independent sources of power, a means of selecting either power source or a means of indicating that the power supply is working satisfactorily.The installation and power supply system shall be such that failure of one instrument, or of the supply from one source, or a fault in any part of the supply system, will not interfere with the proper supply of power from the other source.

Duplicate Instruments

In aircraft involving two-pilot operation it is necessary for each pilot to have his own pilot-static and gyroscopic instruments. Therefore two independent operating systems must be provided and must be so arranged that no fault which might impair the operation of one is likely to impair the operation of both.

Magnetic Compass

The magnetic compass shall be installed so that its accuracy will not be excessively affected by the aircraft vibration or magnetic fields of a permanent or transient nature.

Power plant Instruments

1. Tachometer to measure the rotational speed of a crankshaft or a compressor as appropriate to the type of power plant.2. Cylinder-head temperature indicator for an air-cooled engine to indicate the temperature of the hottest cylinder.3- Carburetor-intake air temperature indicator.4. Oil temperature indicator to show the oil inlet and/or outlet temperature.5. For turbojet and turbo propeller engines a temperature indicator to indicate whether the turbine or exhaust gas temperature is maintained within its limitations.6. Fuel-pressure indicator to indicate pressure at which fuel is being supplied and a means for warning of low pressure.7. Oil pressure indicator to indicate pressure at which oil is being supplied to a lubricating system and a means for warning of low pressure.

INSTRUMENT MECHANISMS ElementsFrom the operating point of view, we may regard an instrument as being made up of the following four principal elements:1. the detecting element, which detects changes in value of the physical quantity or condition presented to it;2. the measuring element, which actually measures the value of the physical quantity or condition in terms of small translation or angular displacements;3. ,the coupling element, by which displacements are magnified and transmitted; and4. the indicating element, which exhibits the value of the measured quantity transmitted by the coupling element, by the relative positions of a pointer or index and a scale.

Four elements Detecting UnitMeasuring UnitCoupling ElementIndicating Element

Mechanism(a) Direct-reading pressure gauge

(b) Airspeed indicator containing measuring, coupling and indicating elements

Lever Mechanism Let us consider first of all the simple Bourdon tube pressure gauge . The Bourdon tube forms both the detecting and measuring elements, a simple link, lever, quadrant and pinion forms the coupling element, while the indicating element is made up of the pointer and scale. This mechanism is of the basic lever type, the lever being, in this case, the complete coupling element. When pressure is applied to the tube it is displaced, such displacement resulting in input and output movements of the coupling and indicating elements respectively, in the directions shown.

Simple lever mechanism lever length which is the distance d between the point of operation of the measuring element and pivoting point of the lever; and lever angle which is the angle 0 between the lever and the link connecting it to the measuring element.

Rod Mechanisms Unlike pure lever mechanisms, rod mechanisms dispense with pin or screw-jointed linkages for the interconnection of component parts and rely on rods in contact with and sliding relative to each other for the generation of the input/output relationship. Contact between the rods under all operating conditions is maintained by the use of a hairspring which tensions the whole mechanism.

These mechanisms find their greatest application in flight instruments Rod mechanisms(a) Sine mechanism (b) Tangent mechanism (c) Double-tangent mechanism

Gears The coupling and indicating elements of many aircraft instruments employ gears in one form or another, for the direct conversion of straight-line or arc-like motion into full rotary motion and for increasing or decreasing the motion. Figure 2.5 illustrates, in schematic