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shutoff lever still attached. The position of these levers suggests that the engine was at
high power forward thrust and that the fuel shutoff lever was in the “run” position.
The analysis of the hydraulic fluid samples taken from the contained cavities showed that
the fluid was in a normal condition. There was no contamination and no moisture as
shown from the FTIR spectra, [Reference 11].
1.12.4 Other Aircraft Components
Only 370 kilograms of electrical wires, connectors and circuit boards of the aircraft were
recovered. The wires were found broken into short lengths. These were sorted according
to the aircraft system wiring, i.e. CVR, FDR, autopilot etc. The examination of the
recovered wires showed no evidence of corrosion, shorting, burning or arcing.
Other parts of the wreckage recovered from the river included the following:
• Portions of the auxiliary power unit (APU).
• Parts of the landing gear assemblies (oleo struts, landing gear door actuators, wheels,
brakes, tire pieces, etc).
• Life rafts, seat frames, seat cushions (which were X-rayed for shrapnel), oxygen
bottles, oxygen masks, medical kits, cabin fittings, partitions, galley equipment and
fixtures, curtains, etc.
• Other actuators
1.13 Medical and Pathological Information
Medical records of the flight crew showed no significant medical history. Medical
personnel, families and friends reported that both pilots were in good health. Due to the
severity of the impact and resulting fragmentation of all persons on board no autopsies
were able to be conducted. There were only six human remains identifiable.
1.14 Fire
There was no evidence found of pre-impact fire.
4 Relation between reading in units and deflection in degrees is given as follows: x units = x degrees + 3.
According to the sign convention, deflection of horizontal stabilizer leading edge up means negative, and
leading edge down means positive (see Figure 13).
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1.15 Survival Aspects
This was not a survivable accident.
1.16 Tests and Research
1.16.1 CVR Circuit Breaker Actuation Test
Upon the completion of data readout by NTSB, the CVR was taken to AlliedSignal on 22
January 1998 for further testing. This testing was an attempt to verify if the termination of
the CVR recording was due to loss of power by the pulling of the CVR circuit breaker or
other means. The result was inconclusive. Therefore other tests had to be performed (see
Appendix F).
There were three tests conducted in a B737-300 aircraft to investigate the CVR circuit
breaker actuation sound signature.
The first test
The first test was carried out on-ground by NTSB and Boeing on 5 February 1998. The
reason for this test was to have quiet ambient condition to provide the best opportunity for
detection of circuit breaker actuation sound signature. The result showed that the CVR
cockpit area microphone did record the CVR circuit breaker actuation. Actuation of a
circuit breaker nearby gave a similar result.
The second test
The test (consisting of on-ground and in-flight tests) was conducted on 14 May 1998 and
15 May 1998 by NTSB.
The purpose of the ground test was to obtain an on-plane, on-ground CVR recording of
the CVR circuit breaker actuation, and the purpose of the flight test was to obtain an onplane,
in-flight CVR recording of the CVR circuit breaker opening. In both tests the
circuit breaker was actuated manually and through the introduction of faults to the
aircraft’s wiring, i.e. short circuit and overload.
The results of these tests were compared with the accident CVR recording sound
signatures. In the short circuit tests a distinctive 400 Hz tone is recorded on one or more
of the CVR channels. No corresponding signatures could be identified on the accident
recording. The same tests found that the area microphone is able to pick up a distinctive
and identifiable snap sound that the circuit breaker makes when it is violently tripped by a
short circuit. (Note: The CVR continues to run for 250 milliseconds before it runs out of
power from the capacitor. As sounds travel about one foot per millisecond, it would take
only six milliseconds to travel the approximately six feet distance from the circuit breaker
to the area microphone. Hence the CVR was able to record the snap sound of the circuit
breaker.)
The overload tests yielded similar results as the short circuit tests except that there was a
slight time delay for the circuit breaker to trip and the snap sound was quieter but still
identifiable. No corresponding sound signatures could be found in the accident recording.
19
The last set of tests was to examine the sound signatures when the CVR circuit breaker
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NTSC Aircraft Accident Report SILKAIR FLIGHT MI 185 BOEING B(15)
