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(1) Obtain fuel and hydraulic fluid samples for analysis. Note where they were obtained and under what conditions.
(2) Relate observation and engineering logic to both available and unavailable physical evidence.
(3) Some parts/components of the aircraft may have been exposed to three different fires/explosions: (a) in-flight, (b) ground impact, and sustained ground. Evidence must be explained in light of the foregoing possibilities.
(4) Some parts/components may have been moved prior to the investigator's involvement. Consider this in assessing the evidence.
(5) Fires in internal areas of the aircraft may leave "chimney" effects evidence.
(6) Look for in-flight fire evidence on parts not subjected to ground fire - could the impact fire ball be the cause?
(7) In-flight fire may leave less metal residue than ground fire because molten metal deposited downstream.
(8) Forced convection in-flight fires and impact fire ball may exceed 3000o F.
(9) Parts subjected to in-flight fire may be more severely burned than parts subjected to ground fire.
(10) Unlike most fires in structural buildings, where fire loadings are somewhat static, the original ignition source in aircraft in-flight fires is not necessarily the area where most severe burning is experienced.
(11) Secondary fires may obscure or mask other evidence.
(12) Water or dirt covering may protect parts from ground fire.
(13) Check for residual fuel odors.
(14) Halon fire extinguishing agents may react with hot components. Lab test may confirm this. (15) Field examination of fire-damaged materials will not give total picture. Reconstruction may be necessary.
(16) Smoke/soot pattern will follow airflow - tail may form downstream from rivets and skin splices.
(17) Soot and discoloration patterns may be due to normal operations. (Check and compare with other aircraft).
(18) Bright scratch marks, scuffs, and smears in soot/discoloration pattern indicates damage after soot/discoloration occurred.
(19) Soot in torn edges of normally protected surfaces indicates fire after damage.
(20) Soot can attach itself by unburned oils and by electrostatic attraction. Will not attach to surfaces over about 700oF.
(21) Parts subjected to ground fire may have twigs, leaves, etc. outlined in soot pattern.
(22) Burn pattern/soot uniformly across and into folds due to impact damage indicate fire prior to damage.
(23) Explosions can occur with little to no thermal or soot evidence. Structure damage may be best evidence of an explosion.
(24) Ground fire smoke/soot pattern sporadic - generally upward.
(25) Rain, snow, and fire-fighting operation may affect soot pattern evidence.
(26) Ground fire flame temperature may range between 1600oF to 2000oF for hydrocarbons.
(27) Discoloration of torn edges and scratches may be due to residual heat in high mass parts.
(28) Aluminum near the molten state and shock loaded will "broomstraw" or "feather".
(29) Molten metal will not deposit on hot objects ( greater than melting temperature of molten metal).
(30) Parts or molten metal droplets may be found along flight path (ensure parts are from mishap aircraft).
(31) Molten metal may be deposited by gravity, air flow, blast wave, or relative motion or a combination of the foregoing.
(32) Melting temperatures of materials will establish minimum exposure temperatures.
(33) Gas released from pressurized containers may given strange burn patterns. Nitrogen will tend to suppress the fire and high pressure air may give evidence similar to oxygen.
(34) Rupture disks/thermal plugs on pressurized containers may give temperature/pressure information.
(35) Discoloration of materials is a time/temperature function.
(36) Oxygen release may result in severe burning often resulting in a white ash deposit.
(37) Normal fire behavior causes upward extension more rapidly than lateral extension (no airflow).
(38) Fire can spread by radiation, convection, and conduction heat transfer.
(39) Witnesses may give a different account of the same event (do not presuppose until several eyewitnesses' statements best support a conclusion). Make a matrix.
(40) A breaking spar can sound like an explosion.
(41) Fuel and hydraulic fluid spray/mist may look like smoke.
(42) Fire/smoke emissions, either internal or external to the aircraft, can be a good clue. Important to identify location, color, intensity, and time of emissions. NOTE: Location of witness and environmental background.
(43) Did survivors/witnesses have the opportunity to discuss the mishap?
(44) Qualification/background of witnesses (one man's "pop" is another man's "crack").
(45) If possible, have key witnesses retrace their actions (location/time).
(46) Determine fire alarm time , response time, rescue efforts, status of fire, equipment used, efforts of fire department, police department, and air control tower as appropriate.
(47) If time factors are questionable, request simulation or rerun, if possible.
(48) Impact or fire may cause loose "B" nuts. If more than a quarter of a turn loose, not the result of a fire.
(49) Electrical arcing damage will be localized, have an eroded appearance, and possible metal splatter. Strands of copper wiring may fuse together and little beads may form on the ends.
(50 Electrostatic discharges (sparks not including lightning) may ignite hydrocarbon fuels. These sparks, however, do not have sufficient energy to leave any direct evidence (pits or discoloration, etc,).
(51) Lightning strikes can result in both spark and arc ignition sources within the aircraft. Both may have sufficient energy to leave thermal evidence. Lightning also may result in hot surface ignition.
(52) Component bonding at resistance less than one-million ohms is acceptable to prevent electrostatic charge build-up on the subject component.
(53) Aircraft grounding will not always prevent electrostatic charge build-up within the aircraft.
(54) Static electricity cannot be identified as the probable ignition source until all other possible ignition sources have been eliminated and a charge generating mechanism is identified.
(55) Parts that separate from the aircraft prior to impact are excellent evidence.
(56) Abnormal functioning subsystems may indicate fire location/time due to thermal damage on electrical wires, fluid lines, or control lines (a fire in a remote dry bay may affect a unique set of subsystem lines/wires, etc.).
(57) Thermal damage of explosion suppression material (internal fuel tank foam) may lead to the wrong conclusion. Damage pattern generally sporadic and unpredictable insofar as establishing a fire pattern.