"Aircraft Accident Investigation Introduction to Aircraft Accident Investigation Procedures Editor"
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 Aircraft Accident Investigation PART I: INTRODUCTION TO ACCIDENT INVESTIGATION Lesson 1: Regulations and Investigative Organizations Lesson 2: The National Transportation Safety Board Aircraft Accident Investigation 4 REGULATIONS AND INVESTIGATIVE ORGANIZATIONS Introduction: There are several reasons why people investigate air- craft accidents. These include: This Airbus A319 was involved in an incident damag- • Corrective actions ing the wingtip (and was subsequently removed). The • Punishment event was written up as an “Aircraft incident” be- • Compensation cause the damage did not fit into the category of “substantial damage.” Whatever the reason, all aircraft accident investigations should attempt the following questions: • requires hospitalization for more than 48 hours, commencing within seven days from the date the • What happened? injury was received • Why did this accident happen? • results in a fracture of any bone (except simple • What can be done to prevent this accident from fractures of fingers, toes, or nose) occurring again in the future? • involves lacerations which cause severe hemorrhage, nerve, muscle, or tendon damage Definitions: • involves injury to any internal organ • involves second or third degree burns, or any burns Aircraft Accident: An occurrence associated with the affecting more than 5 % of the body surface operation of an aircraft which takes place between the • involves verified exposure to infectious substances time any person boards the aircraft with the intention of or injurious radiation flight until such time as all such persons have disem- barked, in which: Substantial Damage: Damage or failure which ad- versely affects the structural strength, performance, or • a person is fatally or seriously injured as a result of flight characteristics of the aircraft, and which would direct contact with the aircraft or its jet blast normally require major repair or replacement of the • the aircraft sustains substantial damage the aircraft affected component. Engine failure or damage limited is missing or completely inaccessible to an engine if only one engine fails or is damaged, bent fairings or cowling, dented skin, small punctured holes Aircraft Incident: an occurrence other than an accident, in the skin or fabric, ground damage to rotor or propel- associated with the operation of an aircraft, which af- 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. fects or could affect the safety of operations. Fatal Injury: Any injury that results in death within 30 The damage to this MD-80 is considered substantial days of the accident because of the effects the damage had on the struc- tural strength, performance, and flight characteris- Serious Injury: An injury which is sustained by a per- tics. The damage to this particular aircraft was con- son in an accident and which: sidered beyond economic repair. Aircraft Accident Investigation 5 Investigative Organizations vestigation. The National Transportation Safety Board (NTSB) Department of Transportation Act (1966) This is an independent board charged with investigating Established the NTSB under the DOT all civil and certain public use aircraft in the United States. In the United States, the NTSB may delegate Independent Safety Board Act (1974) certain investigations to the FAA for investigation. Redefined the NTSB as an independent, non-regulatory There are similar independent boards or groups in Can- organization ada, England, Australia, New Zealand, and several other countries. 1994 Amendment NTSB now investigates certain public use aircraft acci- The Federal Aviation Administration (FAA) dents The FAA is the US government agency responsible for aviation safety in the United States, not investigation. THE NATIONAL TRANSPORTATION Their principle areas of concern are violations of Fed- eral Air Regulations (FARs) and deficiencies in FAA SAFETY BOARD systems or procedures. The FAA may be called upon as Highlights from CFR Title 49 Part 800 a party to the investigation or may be handed the inves- tigation entirely by the NTSB. NTSB Overview International Civil Aviation Organization (ICAO) The Organization: ICAO is an organization that sets the ground rules for The Board itself is composed of five persons appointed member nations involved in an aircraft accident involv- by the President for terms of five years. One of them is ing another member nation. The rules are defined by appointed Chairman for a term of two years. A Vice- ICAO Annex 13. Chairman is likewise appointed for two years. Each appointee must be confirmed by the Senate. The Military The military has complete jurisdiction over accidents The Organization itself consists of about 400 employ- occurring on military installations. Off the military in- ees with offices in Anchorage, Atlanta, Chicago, Dallas stallation, jurisdiction reverts to the local law enforce- / Fort Worth, Denver, Los Angeles, Miami, Parsippany ment structure unless the military can declare the acci- (NJ), Seattle, and Washington D.C. (headquarters). dent scene a national security area. *** See the organizational chart on page 9 (figure 1). Other organizations that might be involved Responsibilities: • OSHA (if the accident involved ground operations) The primary function of the Board is to promote safety • Aircraft owner / operator in transportation. The Board is responsible for the in- • EPA vestigation, determination of facts, conditions, circum- • FBI stances, and the probable cause or causes of: all civil aviation and certain public aircraft events as well as all • United States Customs Service highway, rail, marine, and pipeline events. • Insurance companies The Board makes transportation safety recommenda- History tions to Federal, State, and local agencies as well as private organizations to reduce the likelihood of recur- Air Commerce Act 1926 rences of transportation accidents. Established the requirement to investigate accidents Notification Procedures Civil Aeronautics Act of 1938 Established a three member Air Safety Board for acci- Immediate notification: dent investigation. The operator of any civil aircraft, or any public aircraft not operated by the Armed Forces or an intelligence Civil Aeronautics Board (CAB) amendment (1940) agency of the United States, or any foreign aircraft shall Charged with all civil aviation regulations and the in- immediately, and by the most expeditious means avail- vestigation of accidents. able, notify the nearest National Transportation Safety Board (Board) field office when: Federal Aviation Act of 1958 Created the Federal Aviation Administration and regu- 1. An aircraft accident or any of the following listed lated the CAB to economic regulation and accident in- Aircraft Accident Investigation 6 incidents occur: only as requested by an authorized representative of the Board. • Flight control system malfunction or failure • Inability of any required flight crewmember to Each crewmember, if physically able at the time the perform normal flight duties as a result of in jury or report is submitted, shall attach a statement setting forth illness the facts, conditions, and circumstances relating to the • Failure of structural components of a turbine en- accident or incident as they appear to him. If the crew- gine excluding compressor and turbine blades and member is incapacitated, he shall submit the statement vanes as soon as he is physically able. • In-flight fire • Aircraft collide in flight Accident / Incident Investigation Procedures • Damage to property, other than the aircraft, esti- mated to exceed $25,000 for repair (materials and Responsibilities of the Board labor) or fair market value in the event of total loss The Board is responsible for the organization, conduct, and control of all accident and incident investigations • Inflight failure of electrical system, or hydraulic within the United States, its territories and possessions, system (requiring reliance on sole system for flight where the accident or incident involves any civil air- controls) craft or certain public aircraft, including an investiga- • Sustained loss of thrust by two or more engines tion involving civil or public aircraft on the one hand, • An evacuation of an aircraft in which an emer- and an Armed Forces or intelligence agency aircraft on gency egress system is used the other hand. It is also responsible for investigating accidents/incidents that occur outside the United States, 2. An aircraft is overdue and is believed to have been and which involve civil aircraft and/or certain public involved in an accident. aircraft, when the accident/incident is not in the terri- tory of another country (i.e., in international waters). Information to be given in notification: The Federal Aviation Administration (FAA) may con- • Type, nationality, and registration of the aircraft duct certain aviation investigations (as delegated by the • The name of the owner and operator of the aircraft NTSB), but the Board determines the probable cause of • Pilot-in-command such accidents or incidents. Under no circumstances are • Date and time of the accident aviation investigations where the portion of the investi- • Last point of departure and point of intended land- gation is so delegated to the FAA by the Board consid- ing ered to be joint investigations in the sense of sharing • Position of aircraft in reference to some reasonable responsibility. These investigations remain NTSB in- geographical point vestigations. • Number of persons on board, fatalities, and serious injuries Nature of investigation • Nature of the accident, weather, and damage to the The results of investigations are used to ascertain meas- aircraft ures that would best tend to prevent similar accidents or • Description of any explosives, radioactive material, incidents in the future. The investigation includes the or other dangerous articles carried field investigation (on-scene at the accident, testing, teardown, etc.), report preparation, and, where ordered, Preservation of mail, cargo, and records: a public hearing. The investigation results in Board The operator of an aircraft involved in an accident or conclusions issued in the form of a report or ``brief'' of incident for which notification must be given is respon- the incident or accident. Accident/incident investiga- sible for preserving, to the extent possible, any aircraft tions are fact-finding proceedings with no formal issues wreckage, cargo, and mail aboard the aircraft as well as and no adverse parties. They are not subject to the pro- all records including recording mediums, maintenance, visions of the Administrative Procedure Act, and are and voice recorders pertaining to the operation and not conducted for the purpose of determining the rights maintenance of the aircraft until the Board takes cus- or liabilities of any person. tody. Priority of Board Investigations Reports and statements to be filed The NTSB uses its own criteria to select which acci- The operator of a civil, public, or foreign aircraft shall dents or incidents it chooses to investigate based on file a report on Board Form 6120 within 10 days after current emphasis issues or heightened public interest. an accident or after 7 days if an overdue aircraft is still Regardless of who does the investigation, the NTSB missing. A report on an incident for which immediate retains the final authority on reporting, classification, notification is required by Sec. 830.5(a) shall be filed and determination of the probable cause. Aircraft Accident Investigation 7 Rules for Hearings and Reports Right to Representation Any person interviewed by an authorized representative Nature of Hearing of the Board during the investigation, regardless of the Transportation accident hearings are convened to assist form of the interview (sworn, un-sworn, transcribed, the Board in determining cause or probable cause of an not transcribed, etc.), has the right to be accompanied, accident, in reporting the facts, conditions, and circum- represented, or advised by an attorney or non-attorney stances of the accident, and in ascertaining measures representative. which will tend to prevent accidents and promote trans- portation safety. Such hearings are fact-finding pro- Autopsies ceedings with no formal issues and no adverse parties The Board is authorized to obtain, with or without reim- and are not subject to the provisions of the Administra- bursement, a copy of the report of autopsy performed tive Procedure Act by State or local officials on any person who dies as a result of having been involved in a transportation acci- Sessions Open to the Public dent within the jurisdiction of the Board. The investiga- All hearings shall normally be open to the public tor-in-charge, on behalf of the Board, may order an (subject to the provision that any person present shall autopsy or seek other tests of such persons as may be not be allowed at any time to interfere with the proper necessary to the investigation, provided that to the ex- and orderly functioning of the board of inquiry). tent consistent with the needs of the accident investiga- tion, provisions of local law protecting religious beliefs Accident Report with respect to autopsies shall be observed. The Board will issue a detailed narrative accident report in connection with the investigation into those accidents Parties to the Investigation which the Board determines to warrant such a report. The investigator-in-charge designates parties to partici- The report will set forth the facts, conditions and cir- pate in the investigation. Parties shall be limited to cumstances relating to the accident and the probable those persons, government agencies, companies, and cause thereof, along with any appropriate recommenda- associations whose employees, functions, activities, or tions formulated on the basis of the investigation. products were involved in the accident or incident and who can provide suitable qualified technical personnel Investigation to Remain Open actively to assist in the investigation. Other than the Accident investigations are never officially closed but FAA in aviation cases, no other entity is afforded the are kept open for the submission of new and pertinent right to participate in Board investigations. evidence by any interested person. If the Board finds that such evidence is relevant and probative, it shall be Access to wreckage, mail, records, and cargo made a part of the docket and, where appropriate, par- Only the Board's accident investigation personnel, and ties will be given an opportunity to examine such evi- persons authorized by the investigator-in-charge to par- dence and to comment thereon. ticipate in any particular investigation, examination or testing shall be permitted access to wreckage, records, Types of Accident Reports mail, or cargo in the Board's custody. Narrative Report Release of Information These are the most common reports and generally fol- Release of information during the field investigation, low the facts-analysis-conclusion-recommendation for- particularly at the accident scene, shall be limited to mat. This is the only type of report that analyzes and factual developments, and shall be made only through explains the accident. the Board Member present at the accident scene, the *** See Figure 2 Page 8 representative of the Board's Office of Public Affairs, or the investigator-in-charge. Data Collection Reports These reports are designed to collect data about the Proposed Findings accident in a logical and consistent manner so that they Any person, government agency, company, or associa- may upload easily into a database. These reports often tion whose employees, functions, activities, or products have a prescribed format where the investigator simply were involved in an accident or incident under investi- “fills in the blanks.” gation may submit to the Board written proposed find- ings to be drawn from the evidence produced during the ***See Figure 3 Page 9 course of the investigation, a proposed probable cause, and/or proposed safety recommendations designed to prevent future accidents. Aircraft Accident Investigation 8 Figure 1 - NTSB ORGANIZATIONAL CHART Figure 3 - Narrative Report Aircraft Accident Investigation 9 Figure 3 - Data Collection Report Aircraft Accident Investigation 10 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 Aircraft Accident Investigation 11 PRE-ACCIDENT PLANNING AND PER- Diagramming and Plotting Equipment SONAL SAFETY Diagrams of the accident scene are usually helpful, so be sure to carry the following items: The NTSB Pre-Accident Plan • Pad of ruled paper The Go-Team • Navigation plotter w/ protractor The go team is a group of investigators who are on-call • Measuring tape / ruler for immediate assignment to major accident investiga- • Compass tions. This team consists of an investigator in charge • Calculator / E6-B (IIC) along with in any specialists and laboratory sup- • Notebooks, pencils, pens, etc port that is necessary. Regional investigators may be • Topographical Map used on the Go-Team when headquarters investigators are unavailable. A full Go-Team may consist of the Witness Interviewing Equipment following specialists: air traffic controllers, operations, meteorology, human performance, structures, systems, • Tape Recorders, tapes, batteries powerplants, maintenance, records, survival factors, • Statement forms aircraft performance, CVR, FDR, and metallurgy. The Go-Team must be able to depart to the scene of an acci- Evidence Collection Equipment dent with minimum delay at any time of day (usually a member has a two hour time frame to get to the airport). • Sterile containers • Magnifying glass A Pre-Accident Response Plan • Small tape measure • Flashlight Initial Coordination • Mirror This stage consists of notifying the proper authorities, arranging for transportation to the accident site as well • Tags, labels, markers as overseeing that the wreckage site is secured. Addi- • Plastic bags and sealing tape tionally, this is the time to start collecting and preserv- ing documents relevant to the accident. Resources Photographic Equipment might include the FAA, the aircraft operator, and the manufacturer. Finally, assemble any equipment that • 35mm SLR camera body might become necessary during the investigation. • Electronic flash • Small tripod Investigation Equipment • Ruler - for size reference • Photo log (notebook) • Bring everything you need: do not depend on • Spare batteries and film someone else to bring the equipment for you. • Be prepared to carry whatever you bring: do not Report Writing and Administrative Equipment depend on anyone else to carry it for you. • Accident report forms Also keep in mind - and be prepared - for the environ- • File folders and labels ment at the accident site (i.e. cold, wet, etc.) • Paper • Stapler / paper clips Personal Survival Items • Laptop or notebook computer An investigator must ensure their own safety first - he or she will not be of much use if they are not prepared. Technical Data Some items include: • Parts Catalog or illustrated parts breakdown • Appropriate severe weather clothing including sturdy • Flight manual boots • Color photographs of undamaged aircraft • Gloves (heavy - the wreckage is sharp) and latex gloves • Handbook of common aircraft hardware • Sun protection / insect repellant • Investigation manual and reference • Small first aid kit • Signaling device Other Personal Items • Ear protection • Food and water • Company / agency identification • Expense record Aircraft Accident Investigation 12 • Money - credit cards, checks, cash • How many fatalities? • Passport • What was the cargo? • Immunization records • What was done to the wreckage in order to extin- • Driver’s license guish the fire, rescue the injured, or to remove the bodies? Investigation Overview Conduct an Organizational Meeting Just remember, the key to an efficient investigation includes • Find out who is available to assist • Establish ground rules with respect to the investi- 1. Planning gation and group leadership, wreckage access, 2. Organizing news media, and so on 3. Conducting 4. Concluding Establish Safety Rules Review to personnel onsite some of the dangers associ- Personal Safety ated with aircraft accidents. These include: As previously mentioned, be sure to bring the proper • Chemical hazards clothing and protection for the environment you will be • Pressure vessels working in - be prepared for anything. It is possible that • Mechanical hazards the accident environment will be full of biohazards (i.e. • Pyrotechnic hazards human remains), so as an investigator you will want to • Hygiene hazards - including bloodborne pathogens minimize your exposure to these elements. and human remains • Miscellaneous hazards - radioactivity, fumes, va- Bloodborne Pathogens and other Biohazards pors, etc. Before entering the scene, the NTSB mandates that all persons be made aware of bloodborne pathogens and Conduct an initial walk through of the wreckage how to handle wreckage in this type of environment. This provides a perspective on the accident and facili- Usually, this instruction is in the form of a class presen- tates further discussion on it tation. Personal Protective Equipment (PPE) is a must when working in an accident environment. Obviously, Take initial photographs be careful when handling wreckage; use thick gloves when handling pieces of the aircraft and constantly be Collect perishable evidence vigilant of anything that might pose the risk of causing injury. Investigators might also be required to wear • Fuel samples biohazard suits. More information concerning working with bloodborne pathogens can be found by consulting • Oil / hydraulic fluid samples OSHA 1910.1030. • Loose papers, maps, and charts • Evidence of icing INITIAL ACTIONS • Runway condition • Switch positions Initial On-site Actions • Control surface and trim tab positions • FDRs and CVRs Establish a Base of Operations • Ground scars This should be a location near the scene where you can • Other perishables - anything that is likely to be work, store your equipment, and communicate with the moved or destroyed before it can be investigated rest of the world Inventory the wreckage Establish Liaison with the Local Authorities This allows the investigator to notice any missing parts This includes the police, sheriffs department, fire de- or anything that should not be there partment, and local coroners office. Arrange for Security / Protection of the Wreckage Begin a wreckage diagram Helps to give an overall picture of the accident site Determine what has happened so far Develop a plan • How many total people are involved? Items to think about: Aircraft Accident Investigation 13 • What is the immediate problem? of a wreckage distribution diagram: • Human remains and wreckage recovery • Underwater / inaccessible wreckage • Linear measuring equipment: 100 foot tape meas- • The general direction of the field investigation ure (cloth type is preferable) • Any possible reconstruction • Vertical angle measuring equipment: air navigation plotter ACCIDENT DIAGRAMS • Horizontal angle measuring equipment: magnetic compass Wreckage Diagramming • Plotting equipment: grid (graph) paper 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 Figure X. Single Point Wreckage Diagram • Select a starting point (usually the first impact Wreckage Inventory point), and make a straight line marking off every 50 feet (20 meters). A common phrase used by investigators to assure that • After this, plot the major components of the aircraft all major aircraft sections are accounted for is or anything else of important information relevant “TESTED” to the straight line (see figure x) T: Tips Equipment E: Engines S: Surfaces The following equipment may assist with the creation Aircraft Accident Investigation 14 T: Tail Taking the Pictures E: External Devices D: Doors What pictures should I take? ACCIDENT PHOTOGRAPHY 1. The cardinal rule - photograph the wreckage in reference to the eight points of the compass Photography Background 2. Work in from the perimeter - get the overall view first and then take any close-ups Photography of aircraft accidents is used for two main 3. Take pictures of evidence first - the nice-to know purposes. stuff can wait 4. Take pictures of the overall wreckages (the pictures 1. Photography as evidence in recording medium should tell a story) 2. Photography as a memory aid 5. Take pictures of the surrounding terrain, objects 6. Ground scars, propeller marks When taking photographs, investigators should first 7. Major aircraft structures (nose, wings, tail, fuse- answer the following questions: lage, gear, etc.) 8. Cockpit / cabin / instrument panel • What am I trying to accomplish? 9. Evident damage • Who is going to see the picture / video 10. Separated parts • Should I take back up photo’s with other media? 11. Fire evidence (i.e. soot) • How should I incorporate photos / videos into my How many pictures should be taken? report? As many as possible; film is cheap - the subject is per- ishable Equipment / Supplies Other sources of photos When choosing a camera and film, think of the purpose you will be using it for. • Police, fire, EMS The Camera • Witnesses • News media • 35mm SLR, “point and shoot”, Instant • Auto-focus Follow-up photography • Lenses • Removal of the aircraft wreckage • Flash • Relocation after the wreckage is clear • Back-up • Tear-down analysis What to take with you into the field: • Autopsy • Support Equipment Other information When taking photographs, include a form of label next • Reference aids / markers to the object you are photographing. It may be difficult • Backup identifying certain parts in the photograph when re- • Other viewing the photos at a later time. Film Videography Video recordings are becoming increasingly popular as • Popular brands (don’t risk using a “cheap” brand) they often show a dynamic process. • Note the ASA ratings / speed • User requirements: print film or slides? Advantages: Exposure • On-going narrative • Can illustrate a process • Auto-exposure • Record of investigation • ‘F’ Stop vs. speed vs. focal length • Real-time illustration • Results good for training aid It is important that you be familiar with your camera • Easily edited before you bring it into the field - in other words, do not use your camera for the first time at the accident scene. Aircraft Accident Investigation 15 Disadvantages: Flashover • More “stuff” to carry and keep track of This term is used to describe the situation where an area • Not as good as static scenes or its contents is heated to above its auto-ignition tem- • Lesser quality of image for most “truly” portable perature, but does not ignite due to a shortage of oxy- camcorders gen. When the area is ventilated (oxygen added) the area and its contents ignite simultaneously, sometimes FIRE INVESTIGATION with explosive force. Definitions Flashpoint This is the lowest temperature at which a material will Fire produce a flammable vapor. It is a measure of the vola- This is a collective term for an oxidation reaction pro- tility of the material. ducing heat and light. There are several types of fire. What is a fire? Diffusion Flame / Open Flame A rapid oxidation reaction with the production of heat Elements of a fire and light. A gas flame or a candle flame is termed an open flame – so is the burning of residual fuel follow- • Combustible Material ing the initial “fire ball” during an aircraft impact. • Oxidizer (Usually ordinary air – 20% Oxygen – is sufficient) Deflagration • Ignition: in order for a fire to ignite, the ignition Subsonic gaseous combustion resulting in intense heat source must first raise the temperature of the com- and light and (possibly) a low-level shock wave. Most bustible material (or vapors) in its immediate vicin- aircraft impact “fire balls” are technically deflagration. ity to the ignition temperature of the material. • Heat or energy to sustain the reaction. Detonation A supersonic combustion process occurring in a con- Fire Classes fined or open space characterized by a shock wave pre- ceding the flame front. • Class A • Class B Explosion • Class C Detonation within a confined space resulting in rapid • Class D build-up of pressure and rupture of the containing ves- sel. Explosions may be further categorized as mechani- Significance of Fire cal or chemical. A mechanical explosion involves the rupture of the confining vessel due to a combination of Pre-impact fires in the aircraft are relatively rare, but internal overpressure and loss of vessel integrity. A when they occur, the results are often catastrophic. chemical explosion involves a chemical reaction result- They can be causal to the accident. ing in catastrophic overpressure and subsequent vessel rupture. Post-impact fires are much more common. From an investigation standpoint, they are resultant from the Auto-Ignition Temperature original accident sequence. Post-impact fires are the It is the temperature at which a material will ignite on main threat to accident survivability. its own without any outside source of ignition. Fire scenarios in aviation Flammability Limits These are generally listed as the upper and lower flam- Basic Questions: mability or explosive limits. These describe the highest and lowest concentrations of a fuel /air by volume per- • Where and how did the fire originate cent which will sustain combustion. In other words, a • Where did the fire go (spread)? fuel air mixture below the lower limit is too lean to burn • What did the fire involve? while a mixture above the upper limit is too rich to • What was the fire environment? burn. In considering in-flight fires, the upper and lower • What were the results of the fire? limits may be useful as they vary with temperature and altitude. Thus, for an in-flight fire to occur, the aircraft Variables effecting fires must be operating in a temperature / altitude regime where a combustible fuel-air mixture can exists Aircraft Accident Investigation 16 • Time of exposure to the fire tem that changes the characteristics of the fire. • Temperature of the fire Most inflight fires, though, eventually burn through • Behavior of the flames the structure and are exposed to the slipstream. • Burning characteristics of aircraft materials This adds oxygen to the fire which raises the tem- • Thickness of aircraft materials perature of the fire substantially thus melting mate- • Containment – was there any? rials that would not normally burn in a ground fire (ground fires usually reach temperatures around • Suppression activities (fire extinguishing agents, 2000°F while inflight fires reach temperatures of ARFF, etc.) around 3000°F) Sources of fuel Here is a list of some common sources of fuels contrib- STRUCTURAL INVESTIGATION uting to aircraft fires: Types of structural failures • Aircraft fuel • Oil Overstress The part should have failed (more stress was placed on • Hydraulic fluids the part than it was designed to withstand) • Battery gases • Cargo • Pilot induced: aerobatics, over reaction to turbu- • Waste material lence, improper recovery techniques, any other operation outside of the aircraft’s operating enve- Sources of ignition lope Here is a list of common ignition sources of aircraft • Weather induced overstress: excessive gust loading fires: (turbulence), wind shear • Wake turbulence induced overstress: downwash, • hot engine section parts wingtip vortices • engine exhaust • electrical arc Under-stress • overhead equipment The part should not have failed • bleed air system • static discharge • Faulty manufacture: the part did not meet the de- • lightning sign specifications. • hot brakes / wheels • Faulty repair / modification • friction sparks • Reduction of load bearing capacity: over time, • aircraft heaters metal parts may corrode or develop fatigue cracks. • APU The result of either of these is that the part can no • Inflight galleys longer sustain the specified load. • Ovens / hot-cups • Smoking materials Failures 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 This Boeing 737, Aloha 243, experienced a catastro- • inflight fire effects: if a fire occurs inflight and is phic failure in flight. Metal fatigue caused a crack to contained be the aircraft structure, it will be indis- form in the front section of the fuselage which led to a tinguishable from a ground or post impact fire rapid decompression in flight along with the tearing unless there is some internal forced ventilation sys- away of a large portion of the fuselage. Aircraft Accident Investigation 17 needs to be moved somewhere else (fluid, fuel, Overload failures etc.) The following failures are often associated with an • Power: something that moves the supply through overstress type of failure the system (i.e. pump) • Control: most systems can be controlled, to some • Ductile material: the most obvious feature of ten- extent, by the cockpit; the control often consists of sion fracture in ductile material is the gross plastic an input signal identifying what is desired and a deformation in the area surrounding the fracture. feedback signal identifying what happened The more ductile the material, the more dramatic • Protection: most aircraft systems incorporate pro- will be the necking down of the material on either tection devices to prevent the system from destroy- side of the fracture ing itself (i.e. pressure regulators, fuses, circuit • Brittle material: brittle tension load failures tend to breakers, etc.) have their fracture surface oriented 90 degrees to • Distribution: this provides a means for the systems the tension load. There is little if any plastic defor- medium (i.e. fuel) to be distributed mation. • Application: the purpose of the system Under-stress failures Component Examinations The following issues are common to aircraft accidents The following methods are commonly used when ex- involving the under-stress of certain parts amining aircraft systems components • Fatigue cracking • Photograph it – get pictures of what the part looked • Corrosion like before examining it • Wear • X-ray it – before taking the component apart, con- • Creep (the permanent elongation of a metal part sider an x-ray; this is non-destructive and will pro- due to combination of stress and high temperature) vide a means of examining items that normally would not be available to inspect even if taken Composites apart • Test the part – if possible, add pressure or electric- Construction techniques ity to see if the part actually works • Tear-down analysis – open the part (take apart) for • A composite is any non-homogenous material further examination • the composite most commonly found in structural • Documentation – write down what has been done applications on aircraft is called carbon fiber rein- to the part as well as any conclusions about that forced plastic. This may be found alone or sand- part wiched around a metallic or non-metallic honey- comb structure Specific Systems Properties / Failures Mechanical systems These usually are associated with pilot controls that are • Composites do not develop fatigue cracks; they tied to stick, column, or pedal movements that often develop delaminations, which can be hard to find. involve mechanical items such as cables, pulleys, rods, • When they fail, they do not fail in a ductile or brit- etc. tle manner; they delaminate Cable Systems Questions to ask while examining parts Cables are a popular method of transferring mechanical force somewhere else. They are usually tied into flight • Was the manner of failure consistent with the way control systems and propulsion control systems this part was stressed in flight? • If this part did fail inflight, would that explain the Hydraulic Systems accident? Hydraulic systems use fluids that enable the function of: AIRCRAFT SYSTEMS • Flaps • Landing gear on larger aircraft Systems overview • Certain flight controls • Brakes Common factors to all systems • Other • Supply: involves a source of energy or fluid that Aircraft Accident Investigation 18 Pneumatic Systems RECIPROCATING ENGINES Pneumatic systems usually use a form of compressed gas to power systems such as: Introduction • aircraft pressurization Compared to turbine engines, recips are quite difficult • air conditioning systems 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 Fuel Systems evidence of what was happening at impact. That is why When looking at fuel systems, consider the following so much attention is paid to the propeller. It provides at parts for examination: least an indication of what was going on. We will dis- cuss propellers in the next section. • Fuel vent systems • Fuel return lines Basic Steps • Fuel pumps • Fuel system contaminants Step one in a reciprocating engine investigation is to • Fuel system filters assemble everything that is known so far about the acci- dent. This includes witness statements, radio transmis- Electrical System sions and the basic circumstances of the accidents. Sec- These systems tend to be slightly more complicated. ond, determine what you really need to know about the Areas to loom at might include: engine: • circuit breakers • Was it completely stopped? • emergency power sources • Was it turning at something less than full power? • electrical wiring • Was it turning at something close to full power? Combination systems Complete Engine Failure or Inflight Shutdown Several common combination systems found on aircraft include: If the propeller was feathered, the engine was not rotat- ing at impact and the feathering occurred at some point • electromechanical systems prior to impact. The pilot either deliberately shutdown • hydromechanical systems the engine and feathered the propeller due to some • pneumomechanical systems cockpit indication or the engine failed and the propeller feathered itself because an auto-feather circuit was in- Protection Systems stalled and armed. If the engine merely failed (not de- Common protection systems include: liberately shut down), then we are not likely to find much evidence of the cause in the cockpit. In these • Fire protection situations, a large percentage of engine failures are re- • Ice protection lated to fuel; or lack of it. We should start with a rou- tine check of the fuel system: • Anti-skid systems • Other • Was there fuel on board? • Was the fuel the correct type? Investigation questions about systems • Was the fuel free of contaminants? When examining aircraft systems, the investigator • Could the fuel get to the engine? should consider items such as: • Did the fuel actually get to the engine? • Was the engine getting air? • continuity • Was the engine getting ignition? • integrity • condition Internal Engine Failure • system function • influence on the rest of the aircraft If the inspection above fails to reveal a problem, the next possibility is massive internal damage to the en- • influence on the accident causation 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 Aircraft Accident Investigation 19 any weird noises, there is probably no internal damage to an engine facility where there are hoists, mounting serious enough to keep it from running. stands, tools and good lighting. Taking a turbine engine apart in the field just isn’t practical. There are, how- Engine Did Not Fail, But Was Not Producing Full ever, some basic techniques that can be used by the Power field investigator. While these won’t always provide the final answer, they may give the investigator a pretty There might be several reasons for power loss. good idea of whether the engine contributed signifi- cantly to the accident. Field examination of a turbine • Induction system ice. engine follows a fairly standard protocol. • Induction system failure. • Spark plug failure. • Identify and account for all the major components • Cylinder failure. of the engine. • Lubrication system failure. • Locate and recover any engine-installed recording • Timing failure. devices. • Turbocharger failure. • Check the external appearance of the engine. Look for gross evidence of mechanical failure or Now What? overtemperature. • Obtain fluid samples, particularly the engine oil. Still a mystery? OK, stand back and take an overall • Examine the fuel and oil filters. look at the engine. Do you see any signs of obvious • Examine the chip detectors if installed. Preserve mechanical damage? Do you see any signs of a fire that any chips or “fuzz” for analysis along with the de- seem to emanate from a point? A cracked fuel pump tectors themselves. housing, for example, might not be detectable in the • If possible, use a borescope to examine the engine field, but the fire pattern resulting from it might be ob- internally. vious if you back up a little bit. • Examine the engine mechanisms such as IGVs, variable stators, fuel controls, etc. for evidence of power output. PROPELLERS • Examine the turbine section for evidence of overtemperature operation. Introduction • Examine the accessory drive train for condition and continuity. Propellers are common to both reciprocating engines • Examine the accessories for condition and opera- and turbine engines (turboprops). An examination of tion. the damage to the propeller can sometimes be very use- ful in determining what the engine was doing at the Common Turbine Engine Problems time of impact. • Foreign object damage Evidence of rotation • Volcanic ash ingestion You should be able to examine a propeller and deter- • Compressor stall mine whether it was rotating or not at impact. Some • Accessory failure evidence of rotation: • Thrust reverser failure • Bearing failure • Blades bent opposite the direction of rotation. • Chordwise scratches on the front side of the blades. INSTRUMENT INVESTIGATION • Similar curling or bending at the tips of all blades. • Dings and dents to the leading edge of the blades. Introduction • Torsional damage to the prop shaft or attachment fittings. 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, TURBINE ENGINES 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- Field Investigation Limitations coming highly complex making investigations more complicated. If the engine needs to be disassembled as part of the investigation, it is almost always best to take the engine When examining instruments, treat them as perishable Aircraft Accident Investigation 20 evidence. Any instrument capture, readings, and switch • Maintenance records positions may have changed during / after impact. • Airfield records • Air Traffic Control (ATC) records Methods of investigating • Weather reports 1. Visual presentation – what do the instruments indi- Miscellaneous Reports cate upon a visual inspection 2. Microscopic investigation – this is exactly what it • Accident / incident reports states – a microscopic examination of the part • Sheriff / emergency medical reports 3. Internal examination – this usually involves open- • Service difficulty reports ing up an instrument and examining the internal components such as gears Databases 4. Electrical synchro readout Corporate Event Reporting System (CERS) Pitot / Static system This database system provides a wide variety of opera- tional events concerning operations within a particular The following instruments run off of the pitot / static company. Searches can be categorized by a wide vari- system: ety of factors including event type, aircraft type, a spe- cific aircraft, etc. • Airspeed indicator • Altimeter Flight Operations Quality Assurance (FOQA) • Vertical Speed Indicator (VSI) FOQA takes data broadcasted directly from an aircraft (via a discrete signal) and stores that information to a Other Instruments particular computer. It provides information commonly recorded onto FDRs. This allows personnel within the The following instruments can give important informa- organization to note any trends that are occurring within tion concerning the situation of the accident aircraft the organization (i.e. high speed approaches or ap- proaches that should have been aborted) • attitude indicator • angle of attack WITNESS INTERVIEWING • navigation / communication instruments • engine instruments Introduction • clocks • digital instruments The importance if witnesses varies with the accident. In some cases, they are absolutely vital. There is no recov- Light Bulbs erable wreckage, no survivors and no recorded informa- tion. In other cases, there is plenty of factual informa- Determining whether or not a light bulb was illumi- tion available and the witnesses are merely collabora- nated (or even functioning) may provide important in- tive. In these cases, it is interesting to note the differ- formation to the investigator. It will give the investiga- ences between what the witnesses say and what the tor a chance to see what was actually occurring form facts support. The problem with witness interviewing the pilots perspective – i.e. was the pilot reacting to a lies in the inability to recover accurate information. malfunctioning light or did a warning light burn out. When interviewing, remember that it is exactly this, an AIRCRAFT RECORDS interview and not an interrogation. The investigator is merely trying to establish the facts and not to incrimi- Aircraft records provide investigators a wide variety of nate anyone. information that aids in the investigation. Taking into account the history of a particular aircraft, personnel, or Planning the interview even airline may aid the investigator in noting a particu- lar problem that may have contributed to the accident • Set priorities for witness interviewing – in other sequence. words, who is more important or who will give the most helpful information Types of Records • Obtain contacts for the witnesses • Select a location for interviewing the witness • Corporate records • Prepare for the interview – what questions will you • Operations records ask, will you use a video or tape recorder, etc. Aircraft Accident Investigation 21 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 Aircraft Accident Investigation 22 PART III: ACCIDENT INFORMATION Lesson 12: Mid-Airs and Runway Incursions Lesson 13: Recording Equipment Lesson 14: Human Factors Aircraft Accident Investigation 23 MID-AIR COLLISIONS AND RUNWAY Aircraft Conspicuity INCURSIONS Most mid-air collisions occur in daylight VMC condi- tions. The reason that our ATC system does a pretty Types of Mid-Air Collisions good job of separating IMC traffic during night VMC conditions is that the aircraft lights are highly visible, Associated mid-air collisions therefore decreasing the chances that aircraft will run In this type of mid-air, the two aircraft were flying in into each other. each other’s vicinity and knew it. These typically hap- pen during formation flight or during military combat Cockpit Visibility maneuvers. In civil aviation, mid-air collisions have Few aircraft outside of the military are deliberately built occurred when an aircraft was attempting to inspect the to provide the pilot with good visibility. Also, the cock- landing gear of another aircraft. pit environment often causes the pilot to focus their attention in the cockpit. Associated mid-airs occur because of pilot technique or the operational procedures (or lack of them) in use at ATC Environment the time. The thrust of the investigation is in that direc- If either or both of the aircraft were under air traffic tion. control, then ATC has some degree of involvement in the collision. 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 LAX 1991 - This aircraft was cleared to land while at the same time Voice Recorders if either plane was equipped (see Les- 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 son 13). Third is usually witnesses, if any. The problem avoid the accident. ATC error... 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- Collision Avoidance Equipment tigator would like to know. As more aircraft become equipped with TCAS equip- ment, several questions are bound to arise. Mid-Air Collision Factors • Was either aircraft TCAS equipped? Flight Path / Plane of Collision • If so, was the equipment functioning? This is the relationship of relative bearing, relative clo- • Did the equipment provide the pilots with any sure speed, and the lack of any apparent relative motion warning of the impending collision? is important to the investigator. Another important con- cept is the plane of collision. There are only three possi- Runway Incursions ble planes in which the two aircraft can operate as they approach on collision course: Runway incursions are usually associated with some form of human factors contribution (See Lesson 14). In • Horizontal: Both aircraft are in level flight or have addition, the following factors also contribute to run- vertical speeds which are equal way incursion accidents: • Vertical: This occurs when aircraft are flying the same course and have different vertical speeds • Weather • Combination (neither vertical or horizontal): This • Cockpit environment is probably the most common mid-air situation. • ATC environment Airspeed, vertical speed, and heading are all differ- ent. Aircraft Accident Investigation 24 RECORDING EQUIPMENT • People in their working and living environment Aircraft Flight Recorders • A relationship between people and machines / equipment / procedures Digital Flight Data Recorders (DFDR) • People’s relationship with other people The development of digital FDRs improved both data readout and readout accuracy. The recording medium The most appropriate definition of the applied technol- became Mylar tape and the recording parameters sud- ogy of Human Factors is that it is concerned with opti- denly became anything on the airplane that could be mizing the relationship between people and their activi- measured and reduced to digital forms. DFDRs have the ties by the systematic application of the human sci- capability to record at least 62 different channels or ences, integrated within the framework of systems engi- parameters; the number of actual parameters is almost neering. infinite as one channel can be used for several different parameters. The following key items are always in- The SHEL Model cluded in all DFDRs: In order to better understand human factors, it may be • Time helpful to construct a model that visually represents the • Altitude different factors associated with human factors. • 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 The model is divided into four interfaces: audio circuits. It may also have a channel for the cabin public address (PA) system. The recording is a continu- • liveware - software ous 30 minute loop tape which automatically erases and • liveware - hardware records over itself. At no time is there more than 30 minutes of recording available which means that events • liveware - environment occurring before landing (or crash) are not recorded. • liveware - liveware Other Recording Sources Liveware In the center of the model is man, or Liveware. This is • FAA Tower and Center Radio (audio) tapes the most valuable as well as most flexible component in • FAA Radar tapes the system. At the same time, man is subject to many variations in his performance and suffers many limita- • Flight Service Station tapes tions. Areas to consider when analyzing liveware would • National Weather Service radar tapes include: HUMAN FACTORS • physical size and shape • fuel requirements (food / water) Introduction • Input characteristics • Information processing According to Frank W. Hawkins, human factors is ob- • output characteristics viously about people. It also concerns: Aircraft Accident Investigation 25 • environmental tolerances 5-M Approach to Accident Investigation Liveware - Software The liveware-software interface encompasses the non- Man physical aspects of the system such as procedures, man- Many questions arise when one considers the “why” of ual and checklist layout, symbology, and computer pro- human failures. Successful accident prevention, there- grams fore, necessitates probing beyond the human failure to determine the underlying factors that led to this behav- Liveware - Hardware ior. For example: The L-H interface is one of the most commonly consid- ered interfaces when speaking of machine systems. This • Was the individual physically and mentally capable system concerns how the human interacts with physical of responding properly? If not, why not? hardware. Some examples might include seat design • Did the failure derive from a self-induced state, and control positions. An item to consider in the section such as fatigue or alcohol intoxication? is: was the device in question adapted to meet natural • Had he or she been adequately trained to cope with human characteristics? the situation? • If not, who was responsible for the training defi- Liveware - Environment ciency and why? The liveware - environment concerns how humans per- • Was he or she provided with adequate operational form in a certain environment. Factors might include: information on which to base decisions? • If not, who failed to provide the information and • heat / cold (was there air conditioning or heating?) why? • oxygen / pressurization • Was he or she distracted so that he or she could not • exposure to the elements (i.e. ozone / radiation) give proper care and attention to duties? • disturbing circadian (biological) rhythms • If so, who or what created the distraction and why? Liveware - Liveware These are but of few of the many “why” questions that This last interface concerns the interaction between should be asked during a human-factor investigation. people. Attention is now being turned to the breakdown The answers to these questions are vital for effective of team-work or the system of assuring safety through accident prevention. redundancy. Flight crews function as groups and so group influences can be expected to play a role in deter- Machine mining behavior and performance. Factors affecting the Although the machine (aviation technology) has made L-L interface include: substantial advances, there are still occasions when haz- ards are found in the design, manufacture, or mainte- • leadership nance of aircraft. In fact, a number of accidents can be • crew-cooperation traced to errors in the conceptual, design, and develop- • team-work 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 Tenerife 1977 - The two 747s collided on the runway after the purpose of the operation, to be equally important. Ob- KLM initiated a takeoff without permission while Pan Am had viously the risks associated with different types of op- already announced and begun its takeoff roll. The picture on page 21 shows the aftermath. This is the worst human factors related eration vary considerably. Each category of operation disaster in aviation history. has certain intrinsic hazards that have to be accepted. Aircraft Accident Investigation 26 Management stress. The responsibility for safety and, thus accident preven- tion in any organization ultimately rests with manage- Illusion ment, because only management controls the allocation An erroneous perception of reality due to limitations of of resources. For example, airline management selects sensory receptors and/or the manner in which the infor- the type of aircraft to be purchased, the personnel to fly mation is presented or interpreted. and maintain them, the routes over which they operate, and the training and operating procedures used. Judgement Assessing the significance and priority of information Psychological Factors in a timely manner. The basis for DECISION. Within the broad subject of aviation psychology there Motivation are a number of conditions or situations that could ap- A person’s prioritized value system which influences ply to a particular accident. Here are a few of them his or her behavior. with their definitions as developed jointly by the Life Sciences Division of the USAF Inspection and Safety Peer Pressure Center and the USAF School of Aviation Medicine. A motivating factor stemming from a person’s per- The purpose of this list is to provide the investigator ceived need to meet peer expectations. with the definition of terms likely to be encountered when talking with human performance specialists. Perception The detection and interpretation of environment cues by Affective States one or more of the senses. These are subjective feelings that a person has about his (her) environment, other people or himself. These are Perceptual Set either EMOTIONS, which are brief, but strong in inten- A cognitive or attitudinal framework in which a person sity; or MOODS, which are low in intensity, but long in expects to perceive certain cues and tends to search for duration. those cues to the exclusion of others. Attention Anomalies Situational Awareness These can be CHANNELIZED ATTENTION, which is The ability to keep track of he prioritized significant the focusing upon a limited number of environmental events and conditions in one’s environment. cues to the exclusion of others; or COGNITIVE SATU- RATION in which the amount of information to be Spatial Disorientation processed exceeds an individual’s span of attention. Unrecognized incorrect orientation in space. This can result from a illusion, or an anomaly of attention, or an Distraction anomaly of motivation. The interruption and redirection of attention by environ- mental cues or mental processes. Stress Mental or physical demand requiring some action or Fascination adjustment. 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