Aircraft Accident Investigation Introduction to Aircraft Accident Investigation Procedures Editor: Curt Lewis PE, CSP 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 Sound Spectrum Analysis 24 Human Factors 26 System Safety 29 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 aircraft 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 disembarked, 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 affects 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 person 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 adversely 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 propeller 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 incident 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 damaging the wingtip (and was subsequently removed). The event was written up as an “Aircraft incident” because 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 structural strength, performance, and flight characteristics. The damage to this particular aircraft was considered beyond economic repair. Aircraft Accident Investigation 5 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 Canada, 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 Federal 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 investigation 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 involving 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 installation, jurisdiction reverts to the local law enforcement structure unless the military can declare the accident 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 accident investigation. Civil Aeronautics Board (CAB) amendment (1940) Charged with all civil aviation regulations and the investigation of accidents. Federal Aviation Act of 1958 Created the Federal Aviation Administration and regulated the CAB to economic regulation and accident investigation. 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 accidents 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 employees 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 investigation, determination of facts, conditions, circumstances, 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 recommendations to Federal, State, and local agencies as well as private organizations to reduce the likelihood of recurrences 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 available, notify the nearest National Transportation Safety Board (Board) field office when: 1. An aircraft accident or any of the following listed Aircraft Accident Investigation 6 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, estimated 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 responsible 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 custody. 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 crewmember 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 aircraft or certain public aircraft, including an investigation 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 territory of another country (i.e., in international waters). The Federal Aviation Administration (FAA) may conduct 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 investigation is so delegated to the FAA by the Board considered to be joint investigations in the sense of sharing responsibility. These investigations remain NTSB investigations. Nature of investigation The results of investigations are used to ascertain measures 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 investigations are fact-finding proceedings with no formal issues and no adverse parties. They are not subject to the provisions 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 accidents 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. Aircraft Accident Investigation 7 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 reimbursement, 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 accident within the jurisdiction of the Board. The investigator- 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 extent consistent with the needs of the accident investigation, 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 participate 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 participate 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 association whose employees, functions, activities, or products were involved in an accident or incident under investigation may submit to the Board written proposed findings 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 circumstances of the accident, and in ascertaining measures which will tend to prevent accidents and promote transportation safety. Such hearings are fact-finding proceedings with no formal issues and no adverse parties and are not subject to the provisions of the Administrative 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 circumstances relating to the accident and the probable cause thereof, along with any appropriate recommendations 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, parties will be given an opportunity to examine such evidence and to comment thereon. Types of Accident Reports Narrative Report These are the most common reports and generally follow the facts-analysis-conclusion-recommendation format. 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 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 PERSONAL 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 investigations. This team consists of an investigator in charge (IIC) along with in any specialists and laboratory support 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 accident 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. Additionally, this is the time to start collecting and preserving 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 environment 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 Aircraft Accident Investigation 12 • 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 presentation. 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 department, 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 extinguish 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 investigation and group leadership, wreckage access, news media, and so on Establish Safety Rules Review to personnel onsite some of the dangers associated 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, vapors, etc. Conduct an initial walk through of the wreckage This provides a perspective on the accident and facilitates 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: Aircraft Accident Investigation 13 • 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 identify 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 measure (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, fuselage, 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 perishable 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 reviewing 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 Aircraft Accident Investigation 14 Aircraft Accident Investigation 15 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 producing 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 following 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 confined or open space characterized by a shock wave preceding the flame front. Explosion Detonation within a confined space resulting in rapid build-up of pressure and rupture of the containing vessel. Explosions may be further categorized as mechanical 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 resulting 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 flammability or explosive limits. These describe the highest and lowest concentrations of a fuel /air by volume percent 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 temperature, but does not ignite due to a shortage of oxygen. 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 volatility 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 combustible material (or vapors) in its immediate vicinity 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 Aircraft Accident Investigation 16 • 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 contributing 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 indistinguishable from a ground or post impact fire unless there is some internal forced ventilation system 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 temperature of the fire substantially thus melting materials 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 turbulence, improper recovery techniques, any other operation outside of the aircraft’s operating envelope • 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 design 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 catastrophic 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. Aircraft Accident Investigation 17 Overload failures The following failures are often associated with an overstress type of failure • Ductile material: the most obvious feature of tension 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 deformation. 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 reinforced plastic. This may be found alone or sandwiched around a metallic or non-metallic honeycomb 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 brittle 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 protection devices to prevent the system from destroying 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 examining aircraft systems components • Photograph it – get pictures of what the part looked like before examining it • X-ray it – before taking the component apart, consider an x-ray; this is non-destructive and will provide 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 electricity 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 Aircraft Accident Investigation 18 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 rotation 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 discuss 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 accident. This includes witness statements, radio transmissions and the basic circumstances of the accidents. Second, 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 rotating 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 installed and armed. If the engine merely failed (not deliberately 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 related to fuel; or lack of it. We should start with a routine 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 engine 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 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 obvious 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 useful in determining what the engine was doing at the time of impact. Evidence of rotation You should be able to examine a propeller and determine 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, however, 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 significantly 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 detectors 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 operation. 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 happened prior to impact. Secondly, instruments are becoming highly complex making investigations more complicated. When examining instruments, treat them as perishable Aircraft Accident Investigation 20 evidence. Any instrument capture, readings, and switch positions may have changed during / after impact. Methods of investigating 1. Visual presentation – what do the instruments indicate 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 opening 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 information 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 illuminated (or even functioning) may provide important information to the investigator. It will give the investigator 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 particular 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 operational events concerning operations within a particular company. Searches can be categorized by a wide variety of factors including event type, aircraft type, a specific 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 approaches 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 recoverable wreckage, no survivors and no recorded information. In other cases, there is plenty of factual information available and the witnesses are merely collaborative. In these cases, it is interesting to note the differences 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 incriminate 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. 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 restate something after hearing their statement repeated 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 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 happen 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 direction. 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 toward 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 Lesson 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 immediately before the collision, which is what the investigator would like to know. Mid-Air Collision Factors Flight Path / Plane of Collision This is the relationship of relative bearing, relative closure speed, and the lack of any apparent relative motion is important to the investigator. Another important concept is the plane of collision. There are only three possible 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 different. Aircraft Conspicuity Most mid-air collisions occur in daylight VMC conditions. 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 cockpit 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 equipment, 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 runway 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... Aircraft Accident Investigation 24 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 suddenly 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 included 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 usually has a separate channel for each flight deck crewmember 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 continuous 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 SOUND SPECTRUM ANALYSIS What if we could detect the cause of aircraft damage simply by listening to the sounds recorded in the cockpit? Detecting damage to aircraft after an accident or incident is conducted with the help of various tools and analysis techniques. Cockpit Voice Recorder (CVR) data is a useful tool that investigators use to obtain audio information from the cockpit during the sequence of flight. There are two types of sound that may be analyzed, speech and non-speech audio information. The CVR records audio information on 4 channels. Non-speech information is recorded on channel 1 from the Cockpit Area Microphone (CAM). The CAM records thumps, clicks and other sounds occurring in the cockpit other than speech. Channels 2 and 3 of the CVR record speech audio information from the Captain and First Officer’s audio selector panels. Channel 4 records the audio information from the jump seat/ observer’s radio panel. How are CVR recordings analyzed? The answer: sound spectrum analysis. Sound spectrum analysis is a technique that compares the amplitudes of sounds, and plots the distribution on a three-dimensional graph. This type of analysis depicts changes or modulations in sounds, and it can pinpoint the time when these changes occur. Sound spectrum analysis can be used for analyzing both speech and non-speech audio information. Believe it or not, non-speech sounds are highly important to the investigation of aircraft damage because the background cockpit sounds can reveal problem areas of the aircraft during the time leading up to the accident. Non-speech data from the CAM can be analyzed with sound spectrum analysis to detect whirl flutter, as well as possibly differentiating a bomb explosion from cabin decompression. Spectrum analysis can also be used to confirm that the clicks and thumps recorded by the CAM are simply cockpit controls, and the sound of the aircraft moving through the air. Pan Am Flight 103 disintegrated over Lockerbie, Scotland in 1989 due to a bomb explosion. Aircraft Accident Investigation 25 Speech information recorded by the CVR can be analyzed with spectrum analysis in order to match the recorded voices to the appropriate person. To further understand sound spectrum analysis, you must first understand the physics of sound. Sound is the vibration of any substance. Sound is processed in the form of waves. A wave is a disturbance that travels through a medium. The most common medium that sound waves travel through is air, but it may also travel through substances such as water, metal, or wood. The amplitude of a sound is the height of the wave. Loud sounds will have higher waves than softer waves, resulting in higher amplitude. Sounds are generally measured in cycles, or frequencies. Sound may be represented graphically as a waveform, spectral plot, sonogram, or spectrograph (spectrogram). Spectrographs are the graphical representations used commonly in sound spectrum analysis be cause it presents sounds in a three-dimensional form and it shows a clearer visual of how the amplitudes of various components of a sound change. Sound spectrum analysis is performed with the aid of a personal computer and specialized spectral analysis software. The audio information recorded from the CVR is loaded to the software program, which displays the information in a graphical representation. Each channel from the CVR can be separated to analyze each section of audio information if necessary. Spectrographs can display data in color and in black and white. As previously mentioned aircraft damage can be assessed effectively with the use of a sound spectrum analysis. The National Transportation Safety Board (NTSB)’s Sound Spectrum Group has assisted with many major accident investigations by analyzing the sounds obtained from the CVR and CAM. Such accidents that the sound spectrum group have worked on include American Airlines, Flight 587, in Belle Harbor, New York, and Egypt Air, Flight 990, off the coast of Nantucket, Massachusetts. American Airlines Flight 587 American Airlines, Flight 587, crashed shortly after take off from John F. Kennedy International Airport on November 12, 2001. The aircraft encountered wake turbulence forces from the aircraft that departed just before flight 587, and the vertical tail of the aircraft separated from it and landed over two miles from the main site of impact. The NTSB’s Sound Spectrum Group examined the CVR to document any signals of airframe vibration or flutter. In order to examine this, the team had to analyze the sound of the aircraft while it moved through the air. The airframe will vibrate at a resonant frequency during normal flight. An airframe vibration of the aircraft might change the constant vibration or change the normal steady background noise recorded on the CVR. The team found that the vibration of the aircraft remained relatively constant, and the only change in vibration occurred during the retraction of the landing gear, flaps, and slats. An engine from Flight 587. Another technique was used to examine airframe vibration, which involved a low pass filter applied to the Aircraft Accident Investigation 26 CVR recording. A signal processor calculated the frequency content of the low pass signal that was passed through it. Neither of the two methods identified airframe vibrations or flutter associated with flight 587. The final examination by the Sound Spectrum Group was to document unknown or unusual sounds in the cockpit or from the aircraft. There were many sounds recorded including thumps, clicks, squeaks, rattles, etc. These sounds were later identified as the movements of items in the cockpit during the wake turbulence. The team did not identify any sounds that could be associated with the tail separation of the aircraft. Egypt Air Flight 990 Landing in LAX earlier during the day of the accident. In order to examine the phrases spoken, the sound spectrum group used an analysis technique called voice print methodology. This type of analysis involves comparing the unidentified spoken phrases with known speech sounds. The individual phrases of speech were first broken down and the frequency spectrum of each phrase was plotted. The plots of the frequency spectrum for each phrase were compared with other known speech samples. The team was able to identify the pilot who spoke the phrases because every person has their own unique harmonic variations when they speak. A fundamental (primary) frequency is produced when the vocal cords vibrate. Harmonics are overtones of the fundamental frequency. From this analysis of plotting frequencies and harmonics, the team was able to identify the First Officer as the speaker during the last several minutes of the recording. The sound spectrum group used the plots of the voice print study to determine who was in the cockpit at the end of the recording. After the sound of the cockpit door opening was recorded, the team was able to identify that the door never re-opened, and that the Captain and First Officer were both in the cockpit. Sound Spectrum Analysis has recently been a successful tool to help in the investigations of aircraft accidents. Each recorded sound from the CVR acts as a signature, which can be compared and identified by plotting the sounds in a spectrograph. The research of sound spectrum analysis is fairly new to the accident investigation process. If we knew more about the possibilities of the damage it could detect, then the effects of aircraft damage, such as the disintegration of TWA Flight 800, could be explained more effectively. The cause of TWA 800’s disintegration is still unknown today. HUMAN FACTORS Introduction According to Frank W. Hawkins, human factors is obviously 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 technology of Human Factors is that it is concerned with optimizing the relationship between people and their activities by the systematic application of the human sciences, integrated within the framework of systems engineering. 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 limitations. 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 nonphysical aspects of the system such as procedures, manual and checklist layout, symbology, and computer programs. Liveware - Hardware The L-H interface is one of the most commonly considered 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 perform 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 determining 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, therefore, necessitates probing beyond the human failure to determine the underlying factors that led to this behavior. Aircraft Accident Investigation 27 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. 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 deficiency 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 hazards are found in the design, manufacture, or maintenance of aircraft. In fact, a number of accidents can be traced to errors in the conceptual, design, and development 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 directly 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. Obviously the risks associated with different types of operation vary considerably. Each category of operation has certain intrinsic hazards that have to be accepted. Management The responsibility for safety and, thus accident prevention in any organization ultimately rests with management, 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 apply 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 intensity; 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 SATURATION in which the amount of information to be processed exceeds an individual’s span of attention. Distraction The interruption and redirection of attention by environmental cues or mental processes. Fascination An attention anomaly in which a person observes environmental 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 prolonged 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 information is presented or interpreted. Judgement Assessing the significance and priority of information in a timely manner. The basis for DECISION. Aircraft Accident Investigation 28 Motivation A person’s prioritized value system which influences his or her behavior. Peer Pressure A motivating factor stemming from a person’s perceived 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. SYSTEM SAFETY AND THE SAFETY ORDER OF PRECEDENCE For every incident, there are many near accidents. H.W. Heinrich’s Accident Safety Triangle projects that for every 300 hazards present, there are 29 incidents, and 1 accident. According to this, there are numerous hazards that could potentially develop into the cause of an incident or accident. The key is to identify these hazards in the system and assess them so that a solution may be determined. System Safety is the application of special technical and managerial skills to the systematic, forward-looking identification and control of hazards throughout the life cycle of a project, program, or activity. Simply stated, system safety involves the identifying, evaluating, and addressing of hazards or risk. Its sole purpose is to prevent accidents. The causes of an accident are factors, events, acts, or unsafe conditions which singly, or in combination with other causes, result in the damage or injury that occurred and, if corrected, would have likely prevented or reduced the damage or injury. A hazard is any condition, event, or circumstance, which could induce (cause) an accident. Risk is defined as the probability that an event will occur. There are two major types of risks that are involved in system safety. An informed risk is a risk that has been corrected and assessed, whereas an uninformed risk is a risk that was not identified or was incorrectly measured. The objective of risk management is to obtain an understanding of how to access the various levels of hazards and to gain an insight on logical approaches to deal with those hazards. In order to control these risks, risk management techniques must be enforced. The first step of managing risks is to collect data. Once data is collected, accident precursors (hazards) are identified and evaluated. Finally, countermeasures (solutions) are developed, communicated throughout the organization, and are then implemented in the system. An internal reporting system is an effective way of collecting information about what is going on with respect to safety within an organization. Employees involved in an event report the hazard in the organization’s internal reporting system. From there, hazards can be prioritized, and risk can be assessed and analyzed. Rank each hazard from 1 to 5, with 1 being the most severe and 5 being the least severe. Hazards can be prioritized according to the probability of an accident occurring, and by the severity of an accident that may occur due to the hazard. In order to prioritize hazards, each hazard is ranked according to the most severe or the least severe outcomes. Rankings are assigned with the numbers 1 through 5, 1 being the Aircraft Accident Investigation 29 most severe and 5 being the least severe. It must be understood that we anticipate hazards, not discover them. The Safety Order of Precedence is the hierarchy of solutions that may be implemented to eliminate, control, or reduce a hazard. The highest, most efficient solution is to design for minimum risk or the engineering solution. According to this, the hazard is corrected and eliminated so that it is no longer a threat. For example, if there is a tall tree obstructing takeoff and landing traffic on a runway, the engineering solution would be to cut down the tree. The tree (hazard) is eliminated and normal operations can continue. If a hazard cannot be eliminated, then you should control or guard the hazard. The Control / Guard Solution leaves the hazard in the system, but guards are put up or procedures are changed in order to decrease exposure. In the case of the tree obstructing the runway, if the tree cannot be cut down (eliminated), then choosing to replace the runway threshold would control or guard the hazard. This solution is not the most effective, but the hazard will be reduced in the operation. If it is impossible to eliminate or control the hazard, then warnings to personnel should be issued. This type of solution is known as the Personnel Warning Solution. If the tree in our example cannot be cut down, nor can the runway threshold be moved, then warnings such as safety alerts or Notices to Airmen (NOTAMs) should be issued. From this, personnel who are involved in the situation will be informed of the hazard. The final solution that is used to assess hazards is through the development of training or procedures. This solution, unfortunately, is used the most in the safety industry. The cost of eliminating or controlling the hazard, legal issues, or conflicting company policies may cause safety experts to choose this solution. From this solution, procedures and training for the hazard are applied to reduce risks of catastrophic, hazardous, major, or critical severity. Back to the tree obstruction example, if the tree cannot be cut down, the runway threshold cannot be moved, nor can warnings be issued to reduce the severity of the hazard, procedures and training of pilots to commit a short-field takeoff in order to rotate their aircraft early enough to clear the tree is an example of this final type of hazard solution. System safety also involves risk assessment and risk acceptance. Risks are analyzed by quantifying them according to probability of an accident, level of exposure, and severity of the risk. Risks are ranked in numbers from 1 through 8. An unacceptable risk is ranked with the numbers 1,2, and 3. An undesirable risk is ranked with the number 4. An acceptable risk is ranked with the number 5, 6, 7, and 8, but rankings of 5 and 6 must be closely monitored. If a risk is determined to be acceptable, then the system may continue with the operation as normal. If a risk is determined to be unacceptable, then operations must be discontinued immediately. The key to risk acceptance is to manage the hazard (risk) to a point where it is acceptable. Risks are accepted when 1.) the risk involved is really acceptable, but safety experts don’t like having to accept them due to other constraints, or 2.) safety experts choose not to take any action to eliminate or reduce a hazard. In system safety, there is ALWAYS some amount of risk involved. Some risks can be engineered out of the system, other risks can be controlled or reduced, but it is impossible to eliminate all risks. One of the major problems in safety is that an accident usually must occur in order to prove that a problem exists. This concept is known as blood priority, which states that it is easier to get a hazard corrected if a fatal accident has just occurred. Examples of the blood priority issue can be seen from accidents such as TWA Flight 800, the Grand Canyon mid-air collision, and the September 11, 2001 accidents. Hazards must be identified in order to decrease or eliminate risk in a system and it requires the teamwork of all employees or individuals interacting in Safety Order of Precedence Description Priority Definition Design for Minimum Risk (Engineering Solution) 1 Hazard is corrected and eliminated Control / Guard Solution 2 Guards put up to decrease exposure Personnel Warning Solution 3 Warn personnel if you can’t eliminate / control the hazard Develop Procedures and Training 4 Develop procedures / training to reduce risk (Used most in safety) Risks must be assessed in order to determine whether they are acceptable or unacceptable. a system in order for the process to be effective. Is Safety First? The DECIDE Model • Detect a change has occurred. • Estimate the need to counter the risk. • Choose a desirable outcome. • Identify actions leading to success. • Do take necessary action • Evaluate the results. The DECIDE Model can help us assess hazards and risk.作者: mrmmx 时间: 2010-8-14 17:26:51
