A
ten week course on Aircraft Incidents and Accidents investigation for Pilots and AMTs
Captain
Antonio Carlos Arantes De Biasi
Aircraft accidents and incidents investigation
is not a new procedure. Its roots came from the time the Wright brothers
initiated their pioneering flights. They had a system to record data comprising
their engine RPM, flight time and traveled distance utilizing a rudimentary
contraption that is considered the great grandfather of the actual “black box”
or Flight Data Recorder. They were able to post flight analyze specific
segments of their flights and further adjust the subsequent ones to suit their
research needs. Those were the first steps of what nowadays is called the
sciences of aviation incidents and accidents investigation.
There are several reasons why people
investigate aircraft incidents. These include:
– Corrective actions to prevent future similar incidents or
accidents
– Punishment
– Compensation
In our course of
study we will pursue only the first of the above mentioned reasons.
The main objective of this lecture is to
briefly teach you how and why an incident or accident investigation result is a
powerful tool to enhance safety and promote new procedures and actions that
would contribute to make aviation safer . Our main goal would be to train and
exercise your minds to be kept always open to small details that might in
principle seem trivial but in the end could be the culprit of a tragedy. As an
AMT you should know that the simple event of applying a different than
predicted torque to a bolt might lead to a tragedy of unknown proportions.
As a rule of
thumb every aircraft incident or accident investigation should pursue the
answers for the following questions:
– What happened?
– Why the incident or accident happened?
– What needs to be done to prevent this accident from occurring in
the future?
What is an 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 or is missing or
completely inaccessible.
There are several organizations dedicated
to investigate an aircraft incident or accident, some government agencies other
public and even private ones. Examples:
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, European Union, 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
involv- ing another member nation. The rules are defined by ICAO Annex 13.
The Military
The military has complete
jurisdiction over accidents occurring on military installations. Off the
military installation, jurisdiction reverts to the local law enforce- ment
structure unless the military can declare the accident scene a national security
area.
There are other
organizations that also might be involved in an investigation such as:
–Aircraft Owner / Operator
–FBI
–Insurance companies
There are two
major aspects of an aircraft incident or accident that need to be taken into
account:
1- AVAILABILITY OF THE OCCURRENCE SITE
2- NON-AVAILABILITY OF THE OCCURRENCE
SITE
We will base our study taking into account those two assumptions.
AVAILABILITY OF THE OCCURRENCE SITE
When the
occurrence site is available the first step of the investigation would commence
there. The NTSB has a set of procedures and plans for this situation that will
be used as a guide to our own investigative procedures. They have a full team
of investigators consisting of air traffic controllers, operations, pilots,
meteorology, human performance and behaviour, structures, systems, powerplants,
maintenance, records, survival factors, aircraft performance, Cockpit Voice
Recorders (CVR) and Flight Data Recorders (FDR) specialists and metallurgy.
It’s not our goal to discuss those
procedures or plans; however, we will briefly summarize them and also the
tools, equipment and resources which are available for the field investigator.
Take into account that the following list summarizes the NTSB recommended
hardware for an onsite field trip.
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
• Flight Calculator /
E6-B
• Notebooks, pencils,
pens, etc
• Topographical Map.
Witness Interviewing Equipment
• Tape or Digital
Recorders, 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
• Electronic flash
• Small tripod
• Ruler or measuring tape - for size reference
• Photo log (notebook)
• Spare batteries.
Report Writing and Administrative Equipment
• Accident report forms
• File folders and labels
• Paper
• Stapler / paper clips
• Laptop or notebook
computer
• Printer.
Technical Data
• Parts Catalog or illustrated parts breakdown
• Flight manual
• Color photographs of undamaged aircraft
• Handbook of common aircraft hardware
• Investigation manual
and reference.
Other Personal Items
• Company / agency
identification
• Expense record
• Money - credit cards,
checks, cash
• Passport
• Immunization records
(if required)
• Driver’s license.
Remember that usually
either the NTSB or other authority is taking care of the investigation and your
presence is regarded as a “company’s authorized observer”. Bearing that in your
mind your procedures shall be mostly observational and for that I will also
summarize some rules regarding your personal safety and conduct.
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.
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 (details later)
Observe collected
perishable evidence such as:
• Fuel samples
• Oil / hydraulic fluid samples
• Loose papers, maps, and charts
• Evidence of icing
• Runway condition (if the case)
• Switch positions
• Control surface and trim tab positions
• FDRs and CVRs
• Ground scars
• Other - 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
Wreckage Diagramming
Typical items in an accident
diagram include:
• Location references (roads, buildings, runways, etc.)
• Direction and scale reference
• Elevations / contours (depending on the level of detail)
• Impact heading / scars
• Location of human remains
• Location of major aircraft parts
• Burn areas
• Damage to buildings, structures, trees, etc.
• Location of eye witnesses
Diagramming methods
Grid systems
This is just what it states - a grid is transposed onto an
aerial view of the wreckage so that each piece of the wreckage falls within a
certain square. This helps iden- tify wreckage areas in harsh terrains or
vegetation.
Polar system
In this system, the center of the wreckage site serves as a
reference point. From this point, major pieces of the wreckage are plotted in
relation to there direction and distance form the central wreckage point.
Single Point System
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 1)
figure 1
Equipment
The following equipment may assist with the creation of a
wreckage distribution diagram:
– Linear measuring equipment: 100 foot (minimum)
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”, which means:
T: Tips
E:
Engines
S: Surfaces
T: Tail
E:
External Devices
D: Doors
Photography
Evidently the authority responsible for holding the
investigation will be taking pictures; however, that will not prevent you from
taking too.
What pictures should I take?
1. The
cardinal rule - shoot 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)
Take as many pictures as possible; memory cards are cheap
and the subject is perishable.
When taking pictures, include a form of label next to the
object you are shooting. It may be difficult identifying certain parts in the
photograph when reviewing the photos at a later time.
Fire Investigation
Fire
Fire is a collective noun that depicts 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 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 “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 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 concentration 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 whilst a mixture 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 exist.
Flashover
This
term is used to describe the situation where an area or its contents is heated
above its auto-ignition temperature, but does not ignite due to 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?
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various
reaction products.
Slower oxidative processes like rusting
or digestion are not included
by this definition. The flame is the visible portion of the fire and consists of glowing hot
gases. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside,
the color of the flame and the fire's intensity will be
different.
Elements of a fire
• Combustible Material (fuel)
• 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 (American Standards)
– Class A fire: Ordinary combustibles such as wood, paper, carton, textile, and
PVC;
– Class B fire: Flammable liquid or gaseous fuels such benzene, gasoline, oil,
butane, propane, and natural gas;
– Class C fire: Involving energized electrical equipment, often caused by short
circuits or overheated electrical cables;
– Class D fire: Combustible metals, such as iron, aluminum, sodium, and magnesium;
– Class K fire: Containing a fat
element, such as cooking oil.
Significance of Fire
Pre-impact fires in an aircraft are rare;
however, when they occur, the results are often catastrophic. Most of the cases
they are the cause of 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.
Questions regarding fire scenarios
in aviation
• Where and how did the fire originate
• Where did the fire go (spread)?
• What did the fire involve?
• What was the fire environment?
• What were the results of the fire?
Variables effecting fires
• Time of exposure to the fire
• Temperature of the fire
• Behavior of the flames
• Burning characteristics of aircraft
materials
• Thickness of aircraft materials
• Containment – was there any?
• Suppression activities (fire
extinguishing agents,
ARFF, etc.)
List of common aviation sources of
fuel contributing to aircraft fires:
• Aircraft fuel
• Oil
• Hydraulic fluids
• Battery gases
• Cargo
• Waste material
List of common aviation sources of
ignitions contributing to 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
• In flight galleys
• Ovens / hot-cups
• Smoking materials
In flight fire versus Post-impact
fire
There are two types of evidence that
indicate if a fire originated in flight or post-flight:
1- Indirect evidence – these are just
clues that aid in indicating if there might have been an in flight fire:
– extinguishing system actuated
– oxygen masks dropped
– deactivated electrical circuits
2- Direct evidence
In flight fire effects: if a fire
occurs in flight and is contained by the airframe, it will be indistinguishable
from a ground or a post-impact fire unless there is some internal forced
ventilation system that changes the characteristics of the fire. Most in flight
fires, though, eventually burn through the structure and are exposed to the
slipstream. This adds oxygen to the fire which substantially raises its
temperature thus melting materials that would not normally burn in a ground fire.
Ground fires usually reach
temperatures of 2000ºF whilst in flight fires reach temperatures around 3000ºF.
Another interesting fact is the different discoloration of various materials
after a fire. With this knowledge you may determine how hot a fire actually
was. See figure 2.
figure 2
Airframe Investigation
a-Structural failures
b-Aircraft Systems failures
c-Power Plant failures
d-Instruments failures
a-Structural failures
-Overstress
The part
failed due to more stress placed on it 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.
-Overloading 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
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.
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
failures
• 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.
• 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.
b-Aircraft Systems failures
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
•
Flight controls on heavier aircraft
•
Brakes
• Other.
Pneumatic
Systems
Pneumatic
systems usually use a form of compressed gas (or air) 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 and heaters.
Electrical
System
These
systems tend to be slightly more complicated. Areas to look 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
such as Warning Systems
c-Power
Plant failures
Reciprocating
Engines
Propellers
Turbines
Reciprocating Engines
Introduction
Compared
to turbine engines, reciprocating engines are quite difficult to investigate.
First, they always show evidence of rotationas that is their normal wear
pattern. Second, there is nothing on the reciprocating engines 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 In flight 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
reciprocating engine is a rugged piece of machinery and it frequently survives
an impact and can still be rotated. If it turns without any weird noises, there
is probably no internal damage
serious enough to keep it from running..
Engine
Did Not Fail, But Was Not Producing Full Power
There
might be several reasons for power loss.
• Induction
system ice.
•
Induction system failure.
• Spark
plug failure.
•
Cylinder failure.
•
Lubrication system failure.
•
Timing failure.
•
Turbocharger failure.
Now
What?
Still a
mystery? OK, stand back and take an overall look at the engine. Do you see any
signs of obvious mechanical damage? Do you see any signs of a fire that seem to
emanate from a point? A cracked fuel pump housing, for example, might not be
detectable in the field, but the fire pattern resulting from it might be
obvious
if you
back up a little bit.
Propellers
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.
• Chord
wise 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.
Turbines
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 over temperature.
•
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 over temperature 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.
d-Instruments failures
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 evidence. Any instrument
capture, readings, and switch positions may have changed during / after impact.
Methods
of investigating
• Visual presentation – what do the instruments indicate upon a visual inspection
• Microscopic investigation – this is exactly what it states – a microscopic
examination of the part.
• Internal examination – this usually involves opening up an instrument and
examining the internal components such as gears
• Electrical synchro readout status.
Pitot
/ Static system
The
following instruments run off of the pitot / static system:
•
Airspeed indicator
•
Altimeter
•
Vertical Speed Indicator (VSI)
•
Flight Management Computers
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.
NON-AVAILABILITY OF THE OCCURRENCE SITE
When the availability of the accident
site is either limited or not an option or even if it was predictably modified
by nature’s forces, such as the surface of the water in the middle of an ocean
(or any water extension), rain, wind, storm, a sand storm, tornado or
hurricane, etc. We will need to rely on other sources of information in order
to achieve the desired results during the process of researching the reasons
and factors that might have contributed or mitigated the incident or accident.
Those sources of information will also include human related, historic,
logistic, data base and also previously recorded factors regarding the aircraft
and its operation. Weather, special circumstances, personal, public and
corporation related information may also contain key or contributing factors to
the occurrence. Flight Data Recorders (FDRs) and Cockpit Voice Recorders (CVRs)
are also invaluable source of information.
Here is a summary of information
sources that might be pursued when we face a situation where the site of the
occurrence is not available:
A) FLIGHT AND COCKPIT DATA RECORDERS INFORMATION
B) AIRCRAFT RECORDS
C) CORPORATION RECORDS
D) INSTITUTIONAL FACTORS
E) WEATHER FACTORS
F) HUMAN FACTORS
G) CASES STUDIES RESEARCH
A) FLIGHT AND COCKPIT DATA RECORDERS
INFORMATION
Flight Data Recorders (FDRs) and Cockpit Voice Recorders (CVRs)
are extremely helpful means in determining the probable cause or causes of an
aircraft incident or accident. The FDR contain relevant information regarding
the status of various aircraft systems as well as performance, attitude,
altitude, airspeed, temperature, three axis acceleration ratios and several sub
components operational conditions. Federal Aviation Regulations deals with
general, commuter, corporate and airline operational requirements for the use
of those equipments. Essentially, a CVR is required on general aviation
aircraft that have 10 seats or more and on commuter, corporate that have 6 or
more seats and require two pilots to operate. FDRs are required on public, corporate and on-demand operated
aircraft. Flight Data Recorders allow a considerably great number of flight
parameters (62, in fact) to be recorded aiding invaluable source of data in the
reconstruction of a flight. That data may be used in a flight simulator to
accurately recreate similar conditions that the aircraft experienced before an
incident or accident. The data can also be used to create an animated incident
/ accident simulation to aid the investigators in piecing together the
elements, contributing and mitigating factors of the occurrence.
Examples of parameters recorded by the
FDR:
• Time
• Altitude
• Airspeed
• Heading
• Acceleration (vertical and lateral)
• Pitch attitude
• Roll attitude
• Radio transmission keying
• Thrust / power on each engine
• Flaps and flaps lever or cockpit
control positions
Nowadays all the recordings are digital.
The CVRs on the other hand 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.
B) AIRCRAFT RECORDS
Aircraft records provide the
investigators a wide collection of information that contributes to the
investigative process. Taking into account factors such as described below may
help the investigator notice a particular event or even incident that might
have contributed to the occurrence.
– Operational records
– Maintenance records
Operational records are helpful whilst
tracing a historic chain of events with the aircraft such as its flights,
destinations, type of operations, average duration of its operations and
finally its specific equipment and additions that might eventually altered its
standard lay-out.
Maintenance records show the “life” of
the specific aircraft, its flying time, eventual system failures and consequent
repairs, pre programmed inspections, life expectancy of its engines and various
components, parts replacements due to wear or maintenance requirements. This is
the crucial part for an AMT student as it shows how important a precise and
efficient and effective maintenance work is regarding an aircraft’s safe and
uneventful operation.
C) CORPORATION RECORDS
Those comprise records and reports like
the Corporate Event Reporting Systems (CERS)
which 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.
Other useful corporation record are those
from the Flight Operations Quality Assurance
(FOQA). It takes data broadcasted directly from an aircraft (via discrete
signal) and stores that information to a particular computer database. It
provides information commonly recorded onto FDRs. This allows personnel within
the organization to notice any trends that are occurring within the
organization (i.e. non stabilized approaches, violation of minima, etc).
D) INSTITUTIONAL RECORDS
Those are records regarding private or
public institutions such as Airports and Airfields, Air Traffic Control (ATC)
and Flight Service Stations.
The importance of those sources of information
is crucial when there’s doubt regarding the quality or any influence from the
services which the aircraft has been provided by those institutions. All those institutions
provide means for recording their daily operations that might prove helpful in
an accident or incident investigation.
E) WEATHER FACTORS
Weather phenomena play an extremely
important role in today’s aviation operations. Time tables and schedules are
particularly influenced by those phenomena. The operation of an aircraft itself
is subject to different sets of rules and requirements according to the sort of
weather under it is operating. Cold weather operation, hot weather operation,
rainy regions weather operation as well as local disturbances such a
thunderstorm, lightning, snow storm, sandstorm, volcanic dust and low
visibility are some examples of hazards that influence an aircraft operation.
Areas subject to severe weather phenomena are the most susceptible and most
capable of leading to a situation when an aircraft incident or accident might
happen. The seasons are part of an atmospheric engine that trigger the most
hazardous weather phenomena. The Weather Institutions play a pivotal role
whilst providing precise and accurate information about virtually any airport
or area in the world. Satellite and Doppler radar imagery are invaluable tools
when weather phenomena is suspect onto playing a part in an aircraft incident
or accident. METARs, TAFs, SIGMETs and PIREPs are also important when
researching for clues that might lead to a possible weather relation (or
accountability) to the incident or accident.
F) HUMAN FACTORS
Human factors concern people in their
working and living environments. The relationship between people, machines or
equipment and procedures.
There are several approaches to define
these relationships
Man
Many questions arise when one considers
the “why” of human failures. Men are
subject to many variations in their performance and suffer many limitations.
Successful accidents and incidents prevention, therefore, necessitates probing
beyond the human failure to determine the underlying factors that led to a
distorted human behaviour. 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 / drug intoxication?
– Had the individual been adequately trained to cope with the
situation?
– If not, who was responsible for the training deficiency and why?
– Was the individual provided with adequate operational information
on which to base decisions?
– If not, who failed to provide the information and why?
– Was the individual distracted so that he or she could not give
proper care and attention to the duties?
– If so, who or what created the distraction and why?
These are but a few of the many “why”
questions that should be asked during a human related factor investigation. The
answers to these questions are vital for effective future accident prevention.
Machine
Although the machine (aviation technology) has made substantial progress, there are
still occasions when hazards are found in the design, manufacture, or maintenance of aircraft. In fact, a number of accidents still can be traced to
errors in the concept, manufacturer’s philosophy, design and developing phases
of an aircraft. Modern aircraft design, therefore, attempts to minimize the
effect of any one hazard. For instance, a 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.
On the other hand, manufacturer’s
philosophy regarding operational routines of an aircraft may also contribute to
the occurrence of some incidents and accidents. Unfortunately the former is
usually recognized only after the occurrence of an incident or an accident.
Environment
The environment where the aircraft operations take place, equipment and humans are
employed, and personnel work may directly affect safety. From the accident
prevention viewpoint, this discussion considers the environment to comprise two
parts: the artificial environment and the natural environment. The artificial
environment is the one created from our technology and knowledge. The natural
environment is what the name implies.
Mission
Notwithstanding the man, machine and
environment concepts, some safety experts wisely 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 risks that have to be accepted. The best
example is when commercial flights travel into war zones.
Psychological Factors
Within the broad subject of aviation
psychology there are a number of conditions or situations that could apply to a
particular incident or accident. Here are a few of them with their definitions
as developed jointly by the Life Sciences Division of the United States Air
Force Inspection and Safety Center and the USAF School of Aviation Medicine.
The purpose of this list is to provide the aircraft accidents 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 when a person
observes environmental cues, but fails to respond or react 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 sense of security,
self-confidence or perceived absence of threat.
-Fatigue
Also called exhaustion, lethargy, languidness, languor, lassitude, and listlessness. It is a state of
awareness describing a range of afflictions, usually associated with physical
and/or mental weakness, though varying from a general state of lethargy to a specific work-induced burning sensation within one's muscles.
Physical fatigue is the inability to continue functioning at the level of one's
normal abilities.
-Illusion
An erroneous perception of reality due to
limitations of sensory receptors and / or the manner which the information is
presented or interpreted
-Judgement
Is the evaluation of evidence
in the making
of a decision.
-Motivation
Is a term that refers to a process that
elicits, controls, and sustains certain behaviors. Motivation is a group of
phenomena which affect the nature of an individual's behaviour, the strength of
the behaviour, and the persistence of the behaviour. For instance: An
individual has not eaten, he or she feels hungry, as a response he or she eats
and diminishes feelings of hunger. There are many approaches to motivation:
physiological, behavioural, cognitive, and social. It's the crucial element in
setting and attaining goals—and research shows you can influence your own
levels of motivation and self-control.
-Peer Pressure
Refers to the influence exerted by a peer group in encouraging a person to change his or her attitudes, values, or behaviour in order to conform to group norms. Social groups affected include membership groups, when the individual is "formally" a member (for example,
political
party, trade union), or a
social clique. A person affected by peer pressure may or may not want to belong
to these groups. They may also recognize dissociative groups with which they would not wish to
associate, and thus they behave adversely concerning that group's behaviors.
-Perception
Is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous
system, which in turn result from physical
stimulation of the sense organs. For example, vision involves light striking the retinas of the eyes, smell is mediated by odor molecules and hearing
involves pressure waves. Perception is not the passive receipt of these signals, but can be
shaped by learning, memory and expectation.
-Perceptual set
A cognitive or attitudinal framework in
which a person expects to perceive certain aspects of the available sensory
data to the exclusion of others.
-Situational Awareness
Is the perception of environmental
elements with respect to time and/or space, the comprehension of their meaning,
and the projection of their status after some variable has changed, such as time. It is also a field of study concerned
with perception of the environment critical to decision-makers in complex,
dynamic areas from aviation,
air traffic
control, power plant operations, military command and control,
and emergency
services such as fire fighting
and policing; to more ordinary
but nevertheless complex tasks such as driving an automobile or bicycle.
-Spatial Disorientation
Is the inability to correctly interpret
aircraft attitude, altitude or airspeed, in relation to the Earth or point of
reference. Spatial disorientation is a condition in which an aircraft pilot's perception of direction (proprioception) does not agree with reality. Whilst it can be brought on by
disturbances or disease within the vestibular system, it
is more typically a temporary condition resulting from flight into poor weather
conditions with low or no visibility and the inability to follow instruments
information.
-Stress
Stress typically describes a negative
concept that can have an impact on one’s mental and physical well-being, but it is unclear what exactly defines stress and whether or not
stress is a cause, an effect, or the process connecting the two. With organisms
as complex as humans, stress can take on entirely concrete or abstract meanings
with highly subjective qualities, satisfying definitions of both cause and
effect in ways that can be both tangible and intangible.
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.
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
G) CASES STUDIES RESEARCH
This is by far the most fascinating part
of our study. Regardless of being a powerful tool in the hands of a competent
aircraft incidents and accidents investigator, it’s also one of the most
interesting subjects within the science of incidents and accidents research. Cases
studies research has been responsible for the
solution of a great number of aircraft accidents investigations then regarded
as “unsolvable” or with unknown origins.
In
a case study research,
the researcher gathers data from a number of sources, such as documentation,
interviews, direct observation and physical artifacts. When possible,
corroborative evidence is sought. A database is kept, so that the evidence is
available for subsequent review. The parallel with accident investigation
procedures is evident.
Prior
to analysis, the data may be manipulated in a number of ways. Evidence may be
placed in a matrix of categories, and graphical displays such as flow charts
may be used. Accident investigators place witness evidence in a matrix, so that
apparent inconsistencies may be elucidated, and flow charts have been advocated
in accident investigation [e.g. Benner(1994); Johnson (1994); Zotov, (1996);
Ladkin, (1999)].
The
researcher's initial objective may be descriptive, or to examine theoretical
propositions in the light of the evidence. There are four dominant analytical
techniques in case study research:
•
Pattern matching
•
Explanation building
•
Time series analysis
•
Program logic models.
One of the most known solved cases
attributed to cases study research are the ones related with the Mitsubishi MU2
turboprop airplane.
The
MU-2 was a small, twin turbine-engine aircraft used for commuter airline and
charter
work. Over the years there had been a series of accidents (at least 19) which
were
characterised by loss of control in bad weather. One possibility mooted was
that
water
was getting into the autopilot computer, and producing unanticipated control
inputs,
but the accidents were never satisfactorily resolved.
After
two accidents in rapid succession, BASI performed a special study in which
twelve
such accidents were reviewed, together with a large number of incident
reports.
It was concluded that accumulation of body ice, for which there was no
provision
for removal, could produce a very rapid reduction in airspeed, and also a
stalling
speed much higher than normal. The circumstances of almost all the reports,
for
which sufficient information was available, were compatible with this
conclusion.
It
was recommended that clearance for flight in known icing conditions be
withdrawn.
This ends our study on Aircraft Incidents
and Accidents Investigative Techniques.
References
- AIM/FAR 2011, Aeronautical Information
Manual/Federal Aviation Regulations.
ASA-11-FR-AM-PDF ISBN 1-56027-824-2 978-1-56027-824-5
ASA-11-FR-AM-PDF ISBN 1-56027-824-2 978-1-56027-824-5
- ICAO Annex 13, Aircraft Accident and Incident
Investigation
July 2010 ISBN
978-92-9231-526-9
- BASI.
(1992). MU-2 accident investigation and research report. Canberra: Bureau of Air Safety
Investigation.
- United States Air
Force database and website:
© Antonio Carlos Arantes De Biasi
© Antonio Carlos Arantes De Biasi
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