Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 28
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160 22
prepared to leave the first officer’s position. Until this time, the hot microphone at the first
officer’s position had recorded the first officer’s utterances clearly, as well as some
additional cockpit noises and conversations; however, subsequently, this microphone
(which is a part of the first officer’s headset assembly) provided muffled recordings of
some, but not all, of the cockpit conversations. Command and relief first officer
statements after 0141:11 were recorded more clearly by the CAM.
The study concluded that the recording quality of the first officer’s hot microphone
was excellent while the command first officer wore the headset/microphone and poor
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when the headset/microphone was believed to be stowed.
After 0150:24, the first
officer’s hot microphone stopped recording cockpit conversation and started recording a
sudden increase in background noise. The speech evaluation study indicated that this most
likely occurred because a pilot inadvertently activated the air-to-ground/interphone button
on the back of the control wheel and thereby altered the amplitude of the recording to the
amplitude level set at the individual pilot position.
Speech Sample Information
All speech samples analyzed in the speech study were captured through the CAM
located in the overhead panel. Investigators identified recorded speech samples for six
EgyptAir crewmembers that were in the cockpit at various times during the accident
flight, including the command captain, the relief first officer, the command first officer,
the EgyptAir 767 chief pilot, and two nonduty first officers on board the airplane.
All utterances made after the captain departed the cockpit (at 0148:18) were
analyzed to the extent possible; however, in part because of occasional loud background
noise in the cockpit after that time, only 15 of the 23 utterances recorded by the CAM after
such time were strong enough (relative to background noise) to be analyzed by computer
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for fundamental frequency (pitch) and formant dispersion
information.
Fundamental Frequency and Speech Duration Information
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Research
has shown that fundamental frequency and speech duration vary
characteristically among speakers and often convey information about the speaker’s
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psychological stress. The Safety Board has used the following guidelines
with regard to
fundamental frequency for evaluating the degree of psychological stress experienced by a
speaker:
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The study stated that the exact stowage location of the headset was unknown; however, according to
an EgyptAir representative, it would normally be stowed in the storage console, which located at the first
officer’s right side, or in his flight bag, which is located just aft of the storage console.
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Formants, which determine many aspects of perceived speech, are frequencies at which the vocal
tract above the larynx (acting as a filter because of its normal modes of vibration) will allow maximum
energy to pass from the sound produced by the vocal cords. Formant dispersion refers to the relative spacing
between successive formants.
NTSB/AAB-02/01
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