Aircraft Accident Investigation Procedures飞机事故调查程序

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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.

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