Accident Investigation Manual

Aircraft Accident Investigation Introduction to Aircraft Accident Investigation Procedures

Editor: Curt Lewis PE, CSP

Associate Editor: Corey Burrell

Table of Contents

PART I: INTRODUCTION TO ACCIDENT INVESTIGATION 3 Regulations and Investigative Organizations 4 The National Transportation Safety Board 5 PART II: THE FIELD INVESTIGATION 10 Pre-Accident Planning and Personal Safety 11 Initial Actions 12 Accident Diagrams 13 Accident Photography 14 Fire Investigations 15 Structural Investigations 16 Aircraft Systems 17 Reciprocating Engines 18 Propellers 19 Turbine Engines 19 Instrument Investigation 19 Records 20 Witness Interviewing 20 PART III: ACCIDENT INFORMATION 22 Mid-Airs and Runway Incursions 23 Recording Equipment 24 Human Factors 24

PART I: INTRODUCTION TO ACCIDENT INVESTIGATION

Lesson 1: Regulations and Investigative Organizations Lesson 2: The National Transportation Safety Board

Aircraft Accident Investigation

Aircraft Accident Investigation 4

REGULATIONS AND INVESTIGATIVE ORGANIZATIONS Introduction: There are several reasons why people investigate air-craft accidents. These include: • Corrective actions • Punishment • Compensation Whatever the reason, all aircraft accident investigations should attempt the following questions: • What happened? • Why did this accident happen? • What can be done to prevent this accident from occurring again in the future? Definitions: Aircraft Accident: An occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disem-barked, in which: • a person is fatally or seriously injured as a result of direct contact with the aircraft or its jet blast • the aircraft sustains substantial damage the aircraft is missing or completely inaccessible Aircraft Incident: an occurrence other than an accident, associated with the operation of an aircraft, which af-

fects or could affect the safety of operations. Fatal Injury: Any injury that results in death within 30 days of the accident Serious Injury: An injury which is sustained by a per-son in an accident and which:

• requires hospitalization for more than 48 hours, commencing within seven days from the date the injury was received • results in a fracture of any bone (except simple fractures of fingers, toes, or nose) • involves lacerations which cause severe hemorrhage, nerve, muscle, or tendon damage • involves injury to any internal organ • involves second or third degree burns, or any burns affecting more than 5 % of the body surface • involves verified exposure to infectious substances or injurious radiation Substantial Damage: Damage or failure which ad-versely affects the structural strength, performance, or flight characteristics of the aircraft, and which would normally require major repair or replacement of the affected component. Engine failure or damage limited to an engine if only one engine fails or is damaged, bent fairings or cowling, dented skin, small punctured holes in the skin or fabric, ground damage to rotor or propel-ler blades, and damage to landing gear, wheels, tires, flaps, engine accessories, brakes, or wingtips are not considered substantial damage. Cause: Actions, omissions, events, conditions, or a combination thereof, which led to the accident or inci-dent

Although no passengers or crew were injured, this picture illustrates an accident because the aircraft sustained substantial damage due to the failure of the nose gear to extend.

This Airbus A319 was involved in an incident damag-ing the wingtip (and was subsequently removed). The event was written up as an “Aircraft incident” be-cause the damage did not fit into the category of “substantial damage.”

The damage to this MD-80 is considered substantial because of the effects the damage had on the struc-tural strength, performance, and flight characteris-tics. The damage to this particular aircraft was con-sidered beyond economic repair.


Investigative Organizations The National Transportation Safety Board (NTSB) This is an independent board charged with investigating all civil and certain public use aircraft in the United States. In the United States, the NTSB may delegate certain investigations to the FAA for investigation. There are similar independent boards or groups in Can-ada, England, Australia, New Zealand, and several other countries. The Federal Aviation Administration (FAA) The FAA is the US government agency responsible for aviation safety in the United States, not investigation. Their principle areas of concern are violations of Fed-eral Air Regulations (FARs) and deficiencies in FAA systems or procedures. The FAA may be called upon as a party to the investigation or may be handed the inves-tigation entirely by the NTSB. International Civil Aviation Organization (ICAO) ICAO is an organization that sets the ground rules for member nations involved in an aircraft accident involv-ing another member nation. The rules are defined by ICAO Annex 13. The Military The military has complete jurisdiction over accidents occurring on military installations. Off the military in-stallation, jurisdiction reverts to the local law enforce-ment structure unless the military can declare the acci-dent scene a national security area. Other organizations that might be involved • OSHA (if the accident involved ground operations) • Aircraft owner / operator • EPA • FBI • United States Customs Service • Insurance companies History Air Commerce Act 1926 Established the requirement to investigate accidents Civil Aeronautics Act of 1938 Established a three member Air Safety Board for acci-dent investigation. Civil Aeronautics Board (CAB) amendment (1940) Charged with all civil aviation regulations and the in-vestigation of accidents. Federal Aviation Act of 1958 Created the Federal Aviation Administration and regu-lated the CAB to economic regulation and accident in-

vestigation. Department of Transportation Act (1966) Established the NTSB under the DOT Independent Safety Board Act (1974) Redefined the NTSB as an independent, non-regulatory organization 1994 Amendment NTSB now investigates certain public use aircraft acci-dents THE NATIONAL TRANSPORTATION SAFETY BOARD Highlights from CFR Title 49 Part 800 NTSB Overview The Organization: The Board itself is composed of five persons appointed by the President for terms of five years. One of them is appointed Chairman for a term of two years. A Vice-Chairman is likewise appointed for two years. Each appointee must be confirmed by the Senate. The Organization itself consists of about 400 employ-ees with offices in Anchorage, Atlanta, Chicago, Dallas / Fort Worth, Denver, Los Angeles, Miami, Parsippany (NJ), Seattle, and Washington D.C. (headquarters). *** See the organizational chart on page 9 (figure 1). Responsibilities: The primary function of the Board is to promote safety in transportation. The Board is responsible for the in-vestigation, determination of facts, conditions, circum-stances, and the probable cause or causes of: all civil aviation and certain public aircraft events as well as all highway, rail, marine, and pipeline events. The Board makes transportation safety recommenda-tions to Federal, State, and local agencies as well as private organizations to reduce the likelihood of recur-rences of transportation accidents. Notification Procedures Immediate notification: The operator of any civil aircraft, or any public aircraft not operated by the Armed Forces or an intelligence agency of the United States, or any foreign aircraft shall immediately, and by the most expeditious means avail-able, notify the nearest National Transportation Safety Board (Board) field office when: 1. An aircraft accident or any of the following listed


incidents occur: • Flight control system malfunction or failure • Inability of any required flight crewmember to perform normal flight duties as a result of in jury or illness • Failure of structural components of a turbine engine excluding compressor and turbine blades and vanes • In-flight fire • Aircraft collide in flight • Damage to property, other than the aircraft, esti- mated to exceed $25,000 for repair (materials and labor) or fair market value in the event of total loss • Inflight failure of electrical system, or hydraulic system (requiring reliance on sole system for flight controls) • Sustained loss of thrust by two or more engines • An evacuation of an aircraft in which an emergency egress system is used 2. An aircraft is overdue and is believed to have been involved in an accident. Information to be given in notification: • Type, nationality, and registration of the aircraft • The name of the owner and operator of the aircraft • Pilot-in-command • Date and time of the accident • Last point of departure and point of intended landing • Position of aircraft in reference to some reasonable geographical point • Number of persons on board, fatalities, and serious injuries • Nature of the accident, weather, and damage to the aircraft • Description of any explosives, radioactive material, or other dangerous articles carried Preservation of mail, cargo, and records: The operator of an aircraft involved in an accident or incident for which notification must be given is respon-sible for preserving, to the extent possible, any aircraft wreckage, cargo, and mail aboard the aircraft as well as all records including recording mediums, maintenance, and voice recorders pertaining to the operation and maintenance of the aircraft until the Board takes cus-tody. Reports and statements to be filed The operator of a civil, public, or foreign aircraft shall file a report on Board Form 6120 within 10 days after an accident or after 7 days if an overdue aircraft is still missing. A report on an incident for which immediate notification is required by Sec. 830.5(a) shall be filed

only as requested by an authorized representative of the Board. Each crewmember, if physically able at the time the report is submitted, shall attach a statement setting forth the facts, conditions, and circumstances relating to the accident or incident as they appear to him. If the crew-member is incapacitated, he shall submit the statement as soon as he is physically able. Accident / Incident Investigation Procedures Responsibilities of the Board The Board is responsible for the organization, conduct, and control of all accident and incident investigations within the United States, its territories and possessions, where the accident or incident involves any civil air-craft or certain public aircraft, including an investiga-tion involving civil or public aircraft on the one hand, and an Armed Forces or intelligence agency aircraft on the other hand. It is also responsible for investigating accidents/incidents that occur outside the United States, and which involve civil aircraft and/or certain public aircraft, when the accident/incident is not in the terri-tory of another country (i.e., in international waters). The Federal Aviation Administration (FAA) may con-duct certain aviation investigations (as delegated by the NTSB), but the Board determines the probable cause of such accidents or incidents. Under no circumstances are aviation investigations where the portion of the investi-gation is so delegated to the FAA by the Board consid-ered to be joint investigations in the sense of sharing responsibility. These investigations remain NTSB in-vestigations. Nature of investigation The results of investigations are used to ascertain meas-ures that would best tend to prevent similar accidents or incidents in the future. The investigation includes the field investigation (on-scene at the accident, testing, teardown, etc.), report preparation, and, where ordered, a public hearing. The investigation results in Board conclusions issued in the form of a report or ``brief'' of the incident or accident. Accident/incident investiga-tions are fact-finding proceedings with no formal issues and no adverse parties. They are not subject to the pro-visions of the Administrative Procedure Act, and are not conducted for the purpose of determining the rights or liabilities of any person. Priority of Board Investigations The NTSB uses its own criteria to select which acci-dents or incidents it chooses to investigate based on current emphasis issues or heightened public interest. Regardless of who does the investigation, the NTSB retains the final authority on reporting, classification, and determination of the probable cause.


Right to Representation Any person interviewed by an authorized representative of the Board during the investigation, regardless of the form of the interview (sworn, un-sworn, transcribed, not transcribed, etc.), has the right to be accompanied, represented, or advised by an attorney or non-attorney representative. Autopsies The Board is authorized to obtain, with or without reim-bursement, a copy of the report of autopsy performed by State or local officials on any person who dies as a result of having been involved in a transportation acci-dent within the jurisdiction of the Board. The investiga-tor-in-charge, on behalf of the Board, may order an autopsy or seek other tests of such persons as may be necessary to the investigation, provided that to the ex-tent consistent with the needs of the accident investiga-tion, provisions of local law protecting religious beliefs with respect to autopsies shall be observed. Parties to the Investigation The investigator-in-charge designates parties to partici-pate in the investigation. Parties shall be limited to those persons, government agencies, companies, and associations whose employees, functions, activities, or products were involved in the accident or incident and who can provide suitable qualified technical personnel actively to assist in the investigation. Other than the FAA in aviation cases, no other entity is afforded the right to participate in Board investigations. Access to wreckage, mail, records, and cargo Only the Board's accident investigation personnel, and persons authorized by the investigator-in-charge to par-ticipate in any particular investigation, examination or testing shall be permitted access to wreckage, records, mail, or cargo in the Board's custody. Release of Information Release of information during the field investigation, particularly at the accident scene, shall be limited to factual developments, and shall be made only through the Board Member present at the accident scene, the representative of the Board's Office of Public Affairs, or the investigator-in-charge. Proposed Findings Any person, government agency, company, or associa-tion whose employees, functions, activities, or products were involved in an accident or incident under investi-gation may submit to the Board written proposed find-ings to be drawn from the evidence produced during the course of the investigation, a proposed probable cause, and/or proposed safety recommendations designed to prevent future accidents.

Rules for Hearings and Reports Nature of Hearing Transportation accident hearings are convened to assist the Board in determining cause or probable cause of an accident, in reporting the facts, conditions, and circum-stances of the accident, and in ascertaining measures which will tend to prevent accidents and promote trans-portation safety. Such hearings are fact-finding pro-ceedings with no formal issues and no adverse parties and are not subject to the provisions of the Administra-tive Procedure Act Sessions Open to the Public All hearings shall normally be open to the public (subject to the provision that any person present shall not be allowed at any time to interfere with the proper and orderly functioning of the board of inquiry). Accident Report The Board will issue a detailed narrative accident report in connection with the investigation into those accidents which the Board determines to warrant such a report. The report will set forth the facts, conditions and cir-cumstances relating to the accident and the probable cause thereof, along with any appropriate recommenda-tions formulated on the basis of the investigation. Investigation to Remain Open Accident investigations are never officially closed but are kept open for the submission of new and pertinent evidence by any interested person. If the Board finds that such evidence is relevant and probative, it shall be made a part of the docket and, where appropriate, par-ties will be given an opportunity to examine such evi-dence and to comment thereon. Types of Accident Reports Narrative Report These are the most common reports and generally fol-low the facts-analysis-conclusion-recommendation for-mat. This is the only type of report that analyzes and explains the accident. *** See Figure 2 Page 8 Data Collection Reports These reports are designed to collect data about the accident in a logical and consistent manner so that they may upload easily into a database. These reports often have a prescribed format where the investigator simply “fills in the blanks.” ***See Figure 3 Page 9


Figure 1 - NTSB ORGANIZATIONAL CHART

Figure 3 - Narrative Report


Figure 3 - Data Collection Report


PART II: THE FIELD INVESTIGATION

Lesson 3: Pre-Accident Planning Lesson 4: Initial Actions Lesson 5: Accident Diagrams and Photography Lesson 6: Fire Investigations Lesson 7: Structural Investigations Lesson 8: Aircraft Systems Lesson 9: Reciprocating Engines Lesson 10: Propellers Lesson 11: Turbine Engines Lesson 12: Instrument Investigation Lesson 13: Records Lesson 14: Witness Interviewing


PRE-ACCIDENT PLANNING AND PER-SONAL SAFETY The NTSB Pre-Accident Plan The Go-Team The go team is a group of investigators who are on-call for immediate assignment to major accident investiga-tions. This team consists of an investigator in charge (IIC) along with in any specialists and laboratory sup-port that is necessary. Regional investigators may be used on the Go-Team when headquarters investigators are unavailable. A full Go-Team may consist of the following specialists: air traffic controllers, operations, meteorology, human performance, structures, systems, powerplants, maintenance, records, survival factors, aircraft performance, CVR, FDR, and metallurgy. The Go-Team must be able to depart to the scene of an acci-dent with minimum delay at any time of day (usually a member has a two hour time frame to get to the airport). A Pre-Accident Response Plan Initial Coordination This stage consists of notifying the proper authorities, arranging for transportation to the accident site as well as overseeing that the wreckage site is secured. Addi-tionally, this is the time to start collecting and preserv-ing documents relevant to the accident. Resources might include the FAA, the aircraft operator, and the manufacturer. Finally, assemble any equipment that might become necessary during the investigation. Investigation Equipment • Bring everything you need: do not depend on

someone else to bring the equipment for you. • Be prepared to carry whatever you bring: do not

depend on anyone else to carry it for you. Also keep in mind - and be prepared - for the environ-ment at the accident site (i.e. cold, wet, etc.) Personal Survival Items An investigator must ensure their own safety first - he or she will not be of much use if they are not prepared. Some items include: • Appropriate severe weather clothing including sturdy

boots • Gloves (heavy - the wreckage is sharp) and latex gloves • Sun protection / insect repellant • Small first aid kit • Signaling device • Ear protection • Food and water

Diagramming and Plotting Equipment Diagrams of the accident scene are usually helpful, so be sure to carry the following items: • Pad of ruled paper • Navigation plotter w/ protractor • Measuring tape / ruler • Compass • Calculator / E6-B • Notebooks, pencils, pens, etc • Topographical Map Witness Interviewing Equipment • Tape Recorders, tapes, batteries • Statement forms Evidence Collection Equipment • Sterile containers • Magnifying glass • Small tape measure • Flashlight • Mirror • Tags, labels, markers • Plastic bags and sealing tape Photographic Equipment • 35mm SLR camera body • Electronic flash • Small tripod • Ruler - for size reference • Photo log (notebook) • Spare batteries and film Report Writing and Administrative Equipment • Accident report forms • File folders and labels • Paper • Stapler / paper clips • Laptop or notebook computer Technical Data • Parts Catalog or illustrated parts breakdown • Flight manual • Color photographs of undamaged aircraft • Handbook of common aircraft hardware • Investigation manual and reference Other Personal Items • Company / agency identification • Expense record


• Money - credit cards, checks, cash • Passport • Immunization records • Driver’s license Investigation Overview Just remember, the key to an efficient investigation includes 1. Planning 2. Organizing 3. Conducting 4. Concluding Personal Safety As previously mentioned, be sure to bring the proper clothing and protection for the environment you will be working in - be prepared for anything. It is possible that the accident environment will be full of biohazards (i.e. human remains), so as an investigator you will want to minimize your exposure to these elements. Bloodborne Pathogens and other Biohazards Before entering the scene, the NTSB mandates that all persons be made aware of bloodborne pathogens and how to handle wreckage in this type of environment. Usually, this instruction is in the form of a class presen-tation. Personal Protective Equipment (PPE) is a must when working in an accident environment. Obviously, be careful when handling wreckage; use thick gloves when handling pieces of the aircraft and constantly be vigilant of anything that might pose the risk of causing injury. Investigators might also be required to wear biohazard suits. More information concerning working with bloodborne pathogens can be found by consulting OSHA 1910.1030. INITIAL ACTIONS Initial On-site Actions Establish a Base of Operations This should be a location near the scene where you can work, store your equipment, and communicate with the rest of the world Establish Liaison with the Local Authorities This includes the police, sheriffs department, fire de-partment, and local coroners office. Arrange for Security / Protection of the Wreckage Determine what has happened so far • How many total people are involved?

• How many fatalities? • What was the cargo? • What was done to the wreckage in order to extin-

guish the fire, rescue the injured, or to remove the bodies?

Conduct an Organizational Meeting • Find out who is available to assist • Establish ground rules with respect to the investi-

gation and group leadership, wreckage access, news media, and so on

Establish Safety Rules Review to personnel onsite some of the dangers associ-ated with aircraft accidents. These include: • Chemical hazards • Pressure vessels • Mechanical hazards • Pyrotechnic hazards • Hygiene hazards - including bloodborne pathogens

and human remains • Miscellaneous hazards - radioactivity, fumes, va-

pors, etc. Conduct an initial walk through of the wreckage This provides a perspective on the accident and facili-tates further discussion on it Take initial photographs Collect perishable evidence • Fuel samples • Oil / hydraulic fluid samples • Loose papers, maps, and charts • Evidence of icing • Runway condition • Switch positions • Control surface and trim tab positions • FDRs and CVRs • Ground scars • Other perishables - anything that is likely to be

moved or destroyed before it can be investigated Inventory the wreckage This allows the investigator to notice any missing parts or anything that should not be there Begin a wreckage diagram Helps to give an overall picture of the accident site Develop a plan Items to think about:


• What is the immediate problem? • Human remains and wreckage recovery • Underwater / inaccessible wreckage • The general direction of the field investigation • Any possible reconstruction ACCIDENT DIAGRAMS Wreckage Diagramming Typical items in an accident diagram include: • Location references (roads, buildings, runways,

etc.) • Direction and scale reference • Elevations / contours (depending on the level of

detail) • Impact heading / scars • Location of human remains • Location of major aircraft parts • Burn areas • Damage to buildings, structures, trees, etc. • Location of eye witnesses Diagramming methods Grid systems This is just what it states - a grid is transposed onto an aerial view of the wreckage so that each piece of the wreckage falls within a certain square. This helps iden-tify wreckage areas in harsh terrains or vegetation. Polar system In this system, the center of the wreckage site serves as a reference point. From this point, major pieces of the wreckage are plotted in relation to there direction and distance form the central wreckage point Single Point System This system is similar to the polar system, except the central point does not necessarily have to be the center of the wreckage Straight Line System • This one of the more common and simpler forms of

diagramming available • Select a starting point (usually the first impact

point), and make a straight line marking off every 50 feet (20 meters).

• After this, plot the major components of the aircraft or anything else of important information relevant to the straight line (see figure x)

Equipment The following equipment may assist with the creation

of a wreckage distribution diagram: • Linear measuring equipment: 100 foot tape meas-

ure (cloth type is preferable) • Vertical angle measuring equipment: air navigation

plotter • Horizontal angle measuring equipment: magnetic

compass • Plotting equipment: grid (graph) paper

Wreckage Inventory A common phrase used by investigators to assure that all major aircraft sections are accounted for is “TESTED” T: Tips E: Engines S: Surfaces

Figure X. Single Point Wreckage Diagram

T: Tail E: External Devices D: Doors ACCIDENT PHOTOGRAPHY Photography Background Photography of aircraft accidents is used for two main purposes. 1. Photography as evidence in recording medium 2. Photography as a memory aid When taking photographs, investigators should first answer the following questions: • What am I trying to accomplish? • Who is going to see the picture / video • Should I take back up photo’s with other media? • How should I incorporate photos / videos into my

report? Equipment / Supplies When choosing a camera and film, think of the purpose you will be using it for. The Camera • 35mm SLR, “point and shoot”, Instant • Auto-focus • Lenses • Flash • Back-up What to take with you into the field: • Support Equipment • Reference aids / markers • Backup • Other Film • Popular brands (don’t risk using a “cheap” brand) • Note the ASA ratings / speed • User requirements: print film or slides? Exposure • Auto-exposure • ‘F’ Stop vs. speed vs. focal length It is important that you be familiar with your camera before you bring it into the field - in other words, do not use your camera for the first time at the accident scene.

Taking the Pictures What pictures should I take? 1. The cardinal rule - photograph the wreckage in

reference to the eight points of the compass 2. Work in from the perimeter - get the overall view

first and then take any close-ups 3. Take pictures of evidence first - the nice-to know

stuff can wait 4. Take pictures of the overall wreckages (the pictures

should tell a story) 5. Take pictures of the surrounding terrain, objects 6. Ground scars, propeller marks 7. Major aircraft structures (nose, wings, tail, fuse-

lage, gear, etc.) 8. Cockpit / cabin / instrument panel 9. Evident damage 10. Separated parts 11. Fire evidence (i.e. soot) How many pictures should be taken? As many as possible; film is cheap - the subject is per-ishable Other sources of photos • Police, fire, EMS • Witnesses • News media Follow-up photography • Removal of the aircraft wreckage • Relocation after the wreckage is clear • Tear-down analysis • Autopsy Other information When taking photographs, include a form of label next to the object you are photographing. It may be difficult identifying certain parts in the photograph when re-viewing the photos at a later time. Videography Video recordings are becoming increasingly popular as they often show a dynamic process. Advantages: • On-going narrative • Can illustrate a process • Record of investigation • Real-time illustration • Results good for training aid • Easily edited



Disadvantages: • More “stuff” to carry and keep track of • Not as good as static scenes • Lesser quality of image for most “truly” portable

camcorders FIRE INVESTIGATION Definitions Fire This is a collective term for an oxidation reaction pro-ducing heat and light. There are several types of fire. Diffusion Flame / Open Flame A rapid oxidation reaction with the production of heat and light. A gas flame or a candle flame is termed an open flame – so is the burning of residual fuel follow-ing the initial “fire ball” during an aircraft impact. Deflagration Subsonic gaseous combustion resulting in intense heat and light and (possibly) a low-level shock wave. Most aircraft impact “fire balls” are technically deflagration. Detonation A supersonic combustion process occurring in a con-fined or open space characterized by a shock wave pre-ceding the flame front. Explosion Detonation within a confined space resulting in rapid build-up of pressure and rupture of the containing ves-sel. Explosions may be further categorized as mechani-cal or chemical. A mechanical explosion involves the rupture of the confining vessel due to a combination of internal overpressure and loss of vessel integrity. A chemical explosion involves a chemical reaction result-ing in catastrophic overpressure and subsequent vessel rupture. Auto-Ignition Temperature It is the temperature at which a material will ignite on its own without any outside source of ignition. Flammability Limits These are generally listed as the upper and lower flam-mability or explosive limits. These describe the highest and lowest concentrations of a fuel /air by volume per-cent which will sustain combustion. In other words, a fuel air mixture below the lower limit is too lean to burn while a mixture above the upper limit is too rich to burn. In considering in-flight fires, the upper and lower limits may be useful as they vary with temperature and altitude. Thus, for an in-flight fire to occur, the aircraft must be operating in a temperature / altitude regime where a combustible fuel-air mixture can exists

Flashover This term is used to describe the situation where an area or its contents is heated to above its auto-ignition tem-perature, but does not ignite due to a shortage of oxy-gen. When the area is ventilated (oxygen added) the area and its contents ignite simultaneously, sometimes with explosive force. Flashpoint This is the lowest temperature at which a material will produce a flammable vapor. It is a measure of the vola-tility of the material. What is a fire? Elements of a fire • Combustible Material • Oxidizer (Usually ordinary air – 20% Oxygen – is

sufficient) • Ignition: in order for a fire to ignite, the ignition

source must first raise the temperature of the com-bustible material (or vapors) in its immediate vicin-ity to the ignition temperature of the material.

• Heat or energy to sustain the reaction. Fire Classes • Class A • Class B • Class C • Class D Significance of Fire Pre-impact fires in the aircraft are relatively rare, but when they occur, the results are often catastrophic. They can be causal to the accident. Post-impact fires are much more common. From an investigation standpoint, they are resultant from the original accident sequence. Post-impact fires are the main threat to accident survivability. Fire scenarios in aviation Basic Questions: • Where and how did the fire originate • Where did the fire go (spread)? • What did the fire involve? • What was the fire environment? • What were the results of the fire? Variables effecting fires


• Time of exposure to the fire • Temperature of the fire • Behavior of the flames • Burning characteristics of aircraft materials • Thickness of aircraft materials • Containment – was there any? • Suppression activities (fire extinguishing agents,

ARFF, etc.) Sources of fuel Here is a list of some common sources of fuels contrib-uting to aircraft fires: • Aircraft fuel • Oil • Hydraulic fluids • Battery gases • Cargo • Waste material Sources of ignition Here is a list of common ignition sources of aircraft fires: • hot engine section parts • engine exhaust • electrical arc • overhead equipment • bleed air system • static discharge • lightning • hot brakes / wheels • friction sparks • aircraft heaters • APU • Inflight galleys • Ovens / hot-cups • Smoking materials Inflight fire vs. Post-impact fire There are two types of evidence that indicate if a fire occurred in-flight or post-flight 1. Indirect evidence - these are just clues that aid in

indicating if there might have been an inflight fire: • extinguishing system actuated • oxygen masks dropped • deactivated electrical circuits 2. Direct evidence • inflight fire effects: if a fire occurs inflight and is

contained be the aircraft structure, it will be indis-tinguishable from a ground or post impact fire unless there is some internal forced ventilation sys-

tem that changes the characteristics of the fire. Most inflight fires, though, eventually burn through the structure and are exposed to the slipstream. This adds oxygen to the fire which raises the tem-perature of the fire substantially thus melting mate-rials that would not normally burn in a ground fire (ground fires usually reach temperatures around 2000°F while inflight fires reach temperatures of around 3000°F)

STRUCTURAL INVESTIGATION Types of structural failures Overstress The part should have failed (more stress was placed on the part than it was designed to withstand) • Pilot induced: aerobatics, over reaction to turbu-

lence, improper recovery techniques, any other operation outside of the aircraft’s operating enve-lope

• Weather induced overstress: excessive gust loading (turbulence), wind shear

• Wake turbulence induced overstress: downwash, wingtip vortices

Under-stress The part should not have failed • Faulty manufacture: the part did not meet the de-

sign specifications. • Faulty repair / modification • Reduction of load bearing capacity: over time,

metal parts may corrode or develop fatigue cracks. The result of either of these is that the part can no longer sustain the specified load.

Failures

This Boeing 737, Aloha 243, experienced a catastro-phic failure in flight. Metal fatigue caused a crack to form in the front section of the fuselage which led to a rapid decompression in flight along with the tearing away of a large portion of the fuselage.


Overload failures The following failures are often associated with an overstress type of failure • Ductile material: the most obvious feature of ten-

sion fracture in ductile material is the gross plastic deformation in the area surrounding the fracture. The more ductile the material, the more dramatic will be the necking down of the material on either side of the fracture

• Brittle material: brittle tension load failures tend to have their fracture surface oriented 90 degrees to the tension load. There is little if any plastic defor-mation.

Under-stress failures The following issues are common to aircraft accidents involving the under-stress of certain parts • Fatigue cracking • Corrosion • Wear • Creep (the permanent elongation of a metal part

due to combination of stress and high temperature) Composites Construction techniques • A composite is any non-homogenous material • the composite most commonly found in structural

applications on aircraft is called carbon fiber rein-forced plastic. This may be found alone or sand-wiched around a metallic or non-metallic honey-comb structure

Properties / Failures • Composites do not develop fatigue cracks; they

develop delaminations, which can be hard to find. • When they fail, they do not fail in a ductile or brit-

tle manner; they delaminate Questions to ask while examining parts • Was the manner of failure consistent with the way

this part was stressed in flight? • If this part did fail inflight, would that explain the

accident? AIRCRAFT SYSTEMS Systems overview Common factors to all systems • Supply: involves a source of energy or fluid that

needs to be moved somewhere else (fluid, fuel, etc.)

• Power: something that moves the supply through the system (i.e. pump)

• Control: most systems can be controlled, to some extent, by the cockpit; the control often consists of an input signal identifying what is desired and a feedback signal identifying what happened

• Protection: most aircraft systems incorporate pro-tection devices to prevent the system from destroy-ing itself (i.e. pressure regulators, fuses, circuit breakers, etc.)

• Distribution: this provides a means for the systems medium (i.e. fuel) to be distributed

• Application: the purpose of the system Component Examinations The following methods are commonly used when ex-amining aircraft systems components • Photograph it – get pictures of what the part looked

like before examining it • X-ray it – before taking the component apart, con-

sider an x-ray; this is non-destructive and will pro-vide a means of examining items that normally would not be available to inspect even if taken apart

• Test the part – if possible, add pressure or electric-ity to see if the part actually works

• Tear-down analysis – open the part (take apart) for further examination

• Documentation – write down what has been done to the part as well as any conclusions about that part

Specific Systems Mechanical systems These usually are associated with pilot controls that are tied to stick, column, or pedal movements that often involve mechanical items such as cables, pulleys, rods, etc. Cable Systems Cables are a popular method of transferring mechanical force somewhere else. They are usually tied into flight control systems and propulsion control systems Hydraulic Systems Hydraulic systems use fluids that enable the function of: • Flaps • Landing gear on larger aircraft • Certain flight controls • Brakes • Other


Pneumatic Systems Pneumatic systems usually use a form of compressed gas to power systems such as: • aircraft pressurization • air conditioning systems Fuel Systems When looking at fuel systems, consider the following parts for examination: • Fuel vent systems • Fuel return lines • Fuel pumps • Fuel system contaminants • Fuel system filters Electrical System These systems tend to be slightly more complicated. Areas to loom at might include: • circuit breakers • emergency power sources • electrical wiring Combination systems Several common combination systems found on aircraft include: • electromechanical systems • hydromechanical systems • pneumomechanical systems Protection Systems Common protection systems include: • Fire protection • Ice protection • Anti-skid systems • Other Investigation questions about systems When examining aircraft systems, the investigator should consider items such as: • continuity • integrity • condition • system function • influence on the rest of the aircraft • influence on the accident causation

RECIPROCATING ENGINES Introduction Compared to turbine engines, recips are quite difficult to investigate. First, they always show evidence of ro-tation as that is their normal wear pattern. Second, there is nothing on the recip that consistently captures evidence of what was happening at impact. That is why so much attention is paid to the propeller. It provides at least an indication of what was going on. We will dis-cuss propellers in the next section. Basic Steps Step one in a reciprocating engine investigation is to assemble everything that is known so far about the acci-dent. This includes witness statements, radio transmis-sions and the basic circumstances of the accidents. Sec-ond, determine what you really need to know about the engine: • Was it completely stopped? • Was it turning at something less than full power? • Was it turning at something close to full power? Complete Engine Failure or Inflight Shutdown If the propeller was feathered, the engine was not rotat-ing at impact and the feathering occurred at some point prior to impact. The pilot either deliberately shutdown the engine and feathered the propeller due to some cockpit indication or the engine failed and the propeller feathered itself because an auto-feather circuit was in-stalled and armed. If the engine merely failed (not de-liberately shut down), then we are not likely to find much evidence of the cause in the cockpit. In these situations, a large percentage of engine failures are re-lated to fuel; or lack of it. We should start with a rou-tine check of the fuel system: • Was there fuel on board? • Was the fuel the correct type? • Was the fuel free of contaminants? • Could the fuel get to the engine? • Did the fuel actually get to the engine? • Was the engine getting air? • Was the engine getting ignition? Internal Engine Failure If the inspection above fails to reveal a problem, the next possibility is massive internal damage to the en-gine that just made it quit running. If possible, you might try turning the engine over by hand. The recip is a rugged piece of machinery and it frequently survives an impact and can still be rotated. If it turns without


any weird noises, there is probably no internal damage serious enough to keep it from running. Engine Did Not Fail, But Was Not Producing Full Power There might be several reasons for power loss. • Induction system ice. • Induction system failure. • Spark plug failure. • Cylinder failure. • Lubrication system failure. • Timing failure. • Turbocharger failure. Now What? Still a mystery? OK, stand back and take an overall look at the engine. Do you see any signs of obvious mechanical damage? Do you see any signs of a fire that seem to emanate from a point? A cracked fuel pump housing, for example, might not be detectable in the field, but the fire pattern resulting from it might be ob-vious if you back up a little bit. PROPELLERS Introduction Propellers are common to both reciprocating engines and turbine engines (turboprops). An examination of the damage to the propeller can sometimes be very use-ful in determining what the engine was doing at the time of impact. Evidence of rotation You should be able to examine a propeller and deter-mine whether it was rotating or not at impact. Some evidence of rotation: • Blades bent opposite the direction of rotation. • Chordwise scratches on the front side of the blades. • Similar curling or bending at the tips of all blades. • Dings and dents to the leading edge of the blades. • Torsional damage to the prop shaft or attachment

fittings. TURBINE ENGINES Field Investigation Limitations If the engine needs to be disassembled as part of the investigation, it is almost always best to take the engine

to an engine facility where there are hoists, mounting stands, tools and good lighting. Taking a turbine engine apart in the field just isn’t practical. There are, how-ever, some basic techniques that can be used by the field investigator. While these won’t always provide the final answer, they may give the investigator a pretty good idea of whether the engine contributed signifi-cantly to the accident. Field examination of a turbine engine follows a fairly standard protocol. • Identify and account for all the major components

of the engine. • Locate and recover any engine-installed recording

devices. • Check the external appearance of the engine. Look

for gross evidence of mechanical failure or overtemperature.

• Obtain fluid samples, particularly the engine oil. • Examine the fuel and oil filters. • Examine the chip detectors if installed. Preserve

any chips or “fuzz” for analysis along with the de-tectors themselves.

• If possible, use a borescope to examine the engine internally.

• Examine the engine mechanisms such as IGVs, variable stators, fuel controls, etc. for evidence of power output.

• Examine the turbine section for evidence of overtemperature operation.

• Examine the accessory drive train for condition and continuity.

• Examine the accessories for condition and opera-tion.

Common Turbine Engine Problems • Foreign object damage • Volcanic ash ingestion • Compressor stall • Accessory failure • Thrust reverser failure • Bearing failure INSTRUMENT INVESTIGATION Introduction It is possible to derive a lot of useful information from the cockpit of crashed aircraft, but there are two general problems with cockpit instrument examination. First, the instruments usually indicate the situation at the time of impact, but investigators need to know what hap-pened prior to impact. Secondly, instruments are be-coming highly complex making investigations more complicated. When examining instruments, treat them as perishable


evidence. Any instrument capture, readings, and switch positions may have changed during / after impact. Methods of investigating 1. Visual presentation – what do the instruments indi-

cate upon a visual inspection 2. Microscopic investigation – this is exactly what it

states – a microscopic examination of the part 3. Internal examination – this usually involves open-

ing up an instrument and examining the internal components such as gears

4. Electrical synchro readout Pitot / Static system The following instruments run off of the pitot / static system: • Airspeed indicator • Altimeter • Vertical Speed Indicator (VSI) Other Instruments The following instruments can give important informa-tion concerning the situation of the accident aircraft • attitude indicator • angle of attack • navigation / communication instruments • engine instruments • clocks • digital instruments Light Bulbs Determining whether or not a light bulb was illumi-nated (or even functioning) may provide important in-formation to the investigator. It will give the investiga-tor a chance to see what was actually occurring form the pilots perspective – i.e. was the pilot reacting to a malfunctioning light or did a warning light burn out. AIRCRAFT RECORDS Aircraft records provide investigators a wide variety of information that aids in the investigation. Taking into account the history of a particular aircraft, personnel, or even airline may aid the investigator in noting a particu-lar problem that may have contributed to the accident sequence. Types of Records • Corporate records • Operations records

• Maintenance records • Airfield records • Air Traffic Control (ATC) records • Weather reports Miscellaneous Reports • Accident / incident reports • Sheriff / emergency medical reports • Service difficulty reports Databases Corporate Event Reporting System (CERS) This database system provides a wide variety of opera-tional events concerning operations within a particular company. Searches can be categorized by a wide vari-ety of factors including event type, aircraft type, a spe-cific aircraft, etc. Flight Operations Quality Assurance (FOQA) FOQA takes data broadcasted directly from an aircraft (via a discrete signal) and stores that information to a particular computer. It provides information commonly recorded onto FDRs. This allows personnel within the organization to note any trends that are occurring within the organization (i.e. high speed approaches or ap-proaches that should have been aborted) WITNESS INTERVIEWING Introduction The importance if witnesses varies with the accident. In some cases, they are absolutely vital. There is no recov-erable wreckage, no survivors and no recorded informa-tion. In other cases, there is plenty of factual informa-tion available and the witnesses are merely collabora-tive. In these cases, it is interesting to note the differ-ences between what the witnesses say and what the facts support. The problem with witness interviewing lies in the inability to recover accurate information. When interviewing, remember that it is exactly this, an interview and not an interrogation. The investigator is merely trying to establish the facts and not to incrimi-nate anyone. Planning the interview • Set priorities for witness interviewing – in other

words, who is more important or who will give the most helpful information

• Obtain contacts for the witnesses • Select a location for interviewing the witness • Prepare for the interview – what questions will you

ask, will you use a video or tape recorder, etc.


Conducting the Interview • Make the witness feel at ease – tell them their

rights and the purpose of the interview • Qualify the witness • Encourage the witness to tell a story of the events

that they saw • Repeat the story yourself to make sure you have

the correct facts; the witness may also want to re-state something after hearing their statement re-peated to themselves

• Ask any remaining questions and thank the witness Factors affecting witness reporting A witness interview can be affected by several factors including: • Witness background in aviation/ IQ • Perception of the witness • Emotion / excitements • Interpretation of the ambiguous • Agreement with other witnesses Other reasons for inaccurate statements • Environmental • Physiological • Psychological


PART III: ACCIDENT INFORMATION

Lesson 12: Mid-Airs and Runway Incursions Lesson 13: Recording Equipment Lesson 14: Human Factors


MID-AIR COLLISIONS AND RUNWAY INCURSIONS Types of Mid-Air Collisions Associated mid-air collisions In this type of mid-air, the two aircraft were flying in each other’s vicinity and knew it. These typically hap-pen during formation flight or during military combat maneuvers. In civil aviation, mid-air collisions have occurred when an aircraft was attempting to inspect the landing gear of another aircraft. Associated mid-airs occur because of pilot technique or the operational procedures (or lack of them) in use at the time. The thrust of the investigation is in that direc-tion. Non-associated mid-air collisions These occur between aircraft who are not intentionally flying in each other’s vicinity and neither knows the other is there. The investigation, in these cases, is to-ward the management of the airspace. • Where was each plane suppose to be? • Who had the right of way? • Who could have seen who? In this type of investigation, the first priority is usually the Air Traffic Control records and radar data. Second is probably the Flight Data Recorders and Cockpit Voice Recorders if either plane was equipped (see Les-son 13). Third is usually witnesses, if any. The problem with witnesses is that most of them see the aftermath of the collision. Few see what the planes were doing im-mediately before the collision, which is what the inves-tigator would like to know. Mid-Air Collision Factors Flight Path / Plane of Collision This is the relationship of relative bearing, relative clo-sure speed, and the lack of any apparent relative motion is important to the investigator. Another important con-cept is the plane of collision. There are only three possi-ble planes in which the two aircraft can operate as they approach on collision course: • Horizontal: Both aircraft are in level flight or have

vertical speeds which are equal • Vertical: This occurs when aircraft are flying the

same course and have different vertical speeds • Combination (neither vertical or horizontal): This

is probably the most common mid-air situation. Airspeed, vertical speed, and heading are all differ-ent.

Aircraft Conspicuity Most mid-air collisions occur in daylight VMC condi-tions. The reason that our ATC system does a pretty good job of separating IMC traffic during night VMC conditions is that the aircraft lights are highly visible, therefore decreasing the chances that aircraft will run into each other. Cockpit Visibility Few aircraft outside of the military are deliberately built to provide the pilot with good visibility. Also, the cock-pit environment often causes the pilot to focus their attention in the cockpit. ATC Environment If either or both of the aircraft were under air traffic control, then ATC has some degree of involvement in the collision.

Collision Avoidance Equipment As more aircraft become equipped with TCAS equip-ment, several questions are bound to arise. • Was either aircraft TCAS equipped? • If so, was the equipment functioning? • Did the equipment provide the pilots with any

warning of the impending collision? Runway Incursions Runway incursions are usually associated with some form of human factors contribution (See Lesson 14). In addition, the following factors also contribute to run-way incursion accidents: • Weather • Cockpit environment • ATC environment

LAX 1991 - This aircraft was cleared to land while at the same time a SkyWest Metroliner was cleared to taxi into position and hold on the same runway. The 737 did not see the SkyWest plane in time to avoid the accident. ATC error...


RECORDING EQUIPMENT Aircraft Flight Recorders Digital Flight Data Recorders (DFDR) The development of digital FDRs improved both data readout and readout accuracy. The recording medium became Mylar tape and the recording parameters sud-denly became anything on the airplane that could be measured and reduced to digital forms. DFDRs have the capability to record at least 62 different channels or parameters; the number of actual parameters is almost infinite as one channel can be used for several different parameters. The following key items are always in-cluded in all DFDRs: • Time • Altitude • Airspeed • Heading • Acceleration (vertical) • Pitch attitude • Roll attitude • Radio transmission keying • Thrust / power on each engine • Trailing edge flap or cockpit control Cockpit Voice Recorders (CVRs) The CVR records on Mylar tape and is much easier to install and maintain than the FDR; thus more aircraft are likely to have them. Most CVRs usually have a cockpit area microphone (CAM) usually mounted on the overhead panel between the pilots. This is meant to record cockpit conversation not otherwise recorded through the radio or interphone circuits. The CVR usu-ally has a separate channel for each flight deck crew-member and records everything that goes through those audio circuits. It may also have a channel for the cabin public address (PA) system. The recording is a continu-ous 30 minute loop tape which automatically erases and records over itself. At no time is there more than 30 minutes of recording available which means that events occurring before landing (or crash) are not recorded. Other Recording Sources • FAA Tower and Center Radio (audio) tapes • FAA Radar tapes • Flight Service Station tapes • National Weather Service radar tapes HUMAN FACTORS Introduction According to Frank W. Hawkins, human factors is ob-viously about people. It also concerns:

• People in their working and living environment • A relationship between people and machines /

equipment / procedures • People’s relationship with other people The most appropriate definition of the applied technol-ogy of Human Factors is that it is concerned with opti-mizing the relationship between people and their activi-ties by the systematic application of the human sci-ences, integrated within the framework of systems engi-neering. The SHEL Model In order to better understand human factors, it may be helpful to construct a model that visually represents the different factors associated with human factors.

The model is divided into four interfaces: • liveware - software • liveware - hardware • liveware - environment • liveware - liveware Liveware In the center of the model is man, or Liveware. This is the most valuable as well as most flexible component in the system. At the same time, man is subject to many variations in his performance and suffers many limita-tions. Areas to consider when analyzing liveware would include: • physical size and shape • fuel requirements (food / water) • Input characteristics • Information processing • output characteristics


• environmental tolerances Liveware - Software The liveware-software interface encompasses the non-physical aspects of the system such as procedures, man-ual and checklist layout, symbology, and computer pro-grams Liveware - Hardware The L-H interface is one of the most commonly consid-ered interfaces when speaking of machine systems. This system concerns how the human interacts with physical hardware. Some examples might include seat design and control positions. An item to consider in the section is: was the device in question adapted to meet natural human characteristics? Liveware - Environment The liveware - environment concerns how humans per-form in a certain environment. Factors might include: • heat / cold (was there air conditioning or heating?) • oxygen / pressurization • exposure to the elements (i.e. ozone / radiation) • disturbing circadian (biological) rhythms Liveware - Liveware This last interface concerns the interaction between people. Attention is now being turned to the breakdown of team-work or the system of assuring safety through redundancy. Flight crews function as groups and so group influences can be expected to play a role in deter-mining behavior and performance. Factors affecting the L-L interface include: • leadership • crew-cooperation • team-work

5-M Approach to Accident Investigation Man Many questions arise when one considers the “why” of human failures. Successful accident prevention, there-fore, necessitates probing beyond the human failure to determine the underlying factors that led to this behav-ior. For example: • Was the individual physically and mentally capable

of responding properly? If not, why not? • Did the failure derive from a self-induced state,

such as fatigue or alcohol intoxication? • Had he or she been adequately trained to cope with

the situation? • If not, who was responsible for the training defi-

ciency and why? • Was he or she provided with adequate operational

information on which to base decisions? • If not, who failed to provide the information and

why? • Was he or she distracted so that he or she could not

give proper care and attention to duties? • If so, who or what created the distraction and why? These are but of few of the many “why” questions that should be asked during a human-factor investigation. The answers to these questions are vital for effective accident prevention. Machine Although the machine (aviation technology) has made substantial advances, there are still occasions when haz-ards are found in the design, manufacture, or mainte-nance of aircraft. In fact, a number of accidents can be traced to errors in the conceptual, design, and develop-ment phases of an aircraft. Modern aircraft design, therefore, attempts to minimize the effect of any one hazard. For instance, good design should not only seek to make system failure unlikely, but also ensure that should it nevertheless occur, a single failure will not result in an accident. Medium The medium (environment) in which aircraft operations take place, equipment is used, and personnel work di-rectly affects safety. From the accident prevention viewpoint, this discussion considers the environment to comprise two parts--the natural environment and the artificial environment. Mission Notwithstanding the man, machine, medium concept, some safety experts consider the type of mission, or the purpose of the operation, to be equally important. Ob-viously the risks associated with different types of op-eration vary considerably. Each category of operation has certain intrinsic hazards that have to be accepted.

Tenerife 1977 - The two 747s collided on the runway after the KLM initiated a takeoff without permission while Pan Am had already announced and begun its takeoff roll. The picture on page 21 shows the aftermath. This is the worst human factors related disaster in aviation history.


Management The responsibility for safety and, thus accident preven-tion in any organization ultimately rests with manage-ment, because only management controls the allocation of resources. For example, airline management selects the type of aircraft to be purchased, the personnel to fly and maintain them, the routes over which they operate, and the training and operating procedures used. Psychological Factors Within the broad subject of aviation psychology there are a number of conditions or situations that could ap-ply to a particular accident. Here are a few of them with their definitions as developed jointly by the Life Sciences Division of the USAF Inspection and Safety Center and the USAF School of Aviation Medicine. The purpose of this list is to provide the investigator with the definition of terms likely to be encountered when talking with human performance specialists. Affective States These are subjective feelings that a person has about his (her) environment, other people or himself. These are either EMOTIONS, which are brief, but strong in inten-sity; or MOODS, which are low in intensity, but long in duration. Attention Anomalies These can be CHANNELIZED ATTENTION, which is the focusing upon a limited number of environmental cues to the exclusion of others; or COGNITIVE SATU-RATION in which the amount of information to be processed exceeds an individual’s span of attention. Distraction The interruption and redirection of attention by environ-mental cues or mental processes. Fascination An attention anomaly in which a person observes envi-ronmental cues, but fails to respond to them. Habit pattern interference This is reverting to previously learned response patterns which are inappropriate to the task at hand. Inattention Usually due to a sense of security, self-confidence or perceived absence of threat. Fatigue The progressive decrement in performance due to pro-longed or extreme mental or physical activity, sleep deprivation, disrupted diurnal cycles, or life event

stress. Illusion An erroneous perception of reality due to limitations of sensory receptors and/or the manner in which the infor-mation is presented or interpreted. Judgement Assessing the significance and priority of information in a timely manner. The basis for DECISION. Motivation A person’s prioritized value system which influences his or her behavior. Peer Pressure A motivating factor stemming from a person’s per-ceived need to meet peer expectations. Perception The detection and interpretation of environment cues by one or more of the senses. Perceptual Set A cognitive or attitudinal framework in which a person expects to perceive certain cues and tends to search for those cues to the exclusion of others. Situational Awareness The ability to keep track of he prioritized significant events and conditions in one’s environment. Spatial Disorientation Unrecognized incorrect orientation in space. This can result from a illusion, or an anomaly of attention, or an anomaly of motivation. Stress Mental or physical demand requiring some action or adjustment.

Accident Investigation Manual

Documents

aircraft accidents

particular aircraft

accident investigation

accident serious injury

inaccessible aircraft

ground damage

accident informationmidairs

tendon damage