Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 29
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•
An increase in fundamental frequency of about 30 percent (compared with that
individual’s speech in a relaxed condition) would be characteristic of a stage 1
level of stress, which could result in the speaker’s focused attention and
improved performance.
•
An increase in fundamental frequency of between 50 to 150 percent would be
characteristic of a stage 2 level of stress, which could result in the speaker’s
performance becoming hasty and abbreviated; however, the speaker’s
performance would not display gross mistakes.
•
An increase in fundamental frequency of between 100 to 200 percent would be
characteristic of a stage 3 level of stress, or panic, which could result in the
speaker’s inability to think or function logically or productively.
On the basis of these guidelines, the CVR speech study concluded that the relief
first officer exhibited no more than a 25 percent increase in fundamental frequency,
compared to what he exhibited during routine flight, when he made any of his “I rely on
God” statements and when he stated, “it’s shut,” during the emergency sequence.
However, the speech study concluded that the command captain exhibited an increase in
fundamental frequency of 29 percent when he stated, “what’s happening?,” shortly after
he returned to the cockpit and of between 47 and 65 percent when he stated, “get away in
the engines,” “shut the engines,” “pull,” and “pull with me,” during the emergency
sequence, compared to what he exhibited during routine flight.
Previous research has also shown that speech duration often becomes shorter (that
is, speaking rate becomes faster) when psychological stress increases. Speech duration
measurements were performed on the phrase “I rely on God” (repeated by the relief first
officer 11 times between 0148:39 and 0150:08). The CVR transcript indicated that the first
utterance of the phrase “I rely on God” was spoken faintly, about 1 minute 6 seconds
before the autopilot was disconnected, and had a duration of 1.02 seconds. The second
utterance of this phrase, which occurred about 5 seconds before the throttle levers were
moved to idle and while the airplane was still in level flight, had a duration of 0.81 second.
The remaining nine utterances of this phrase, which began about 8 seconds later (as the
airplane began its abrupt nose-down pitch and steep descent), varied in duration from 0.73
to 0.87 seconds, with pauses of 0.51 and 0.70 seconds between successive utterances.
50
For additional information, see Williams, C. E. and Stevens, K. N. 1981. “Vocal Correlates of
Emotional States.” Speech Evaluation in Psychiatry. Grune & Stratton. New York, New York; Ruiz, R.;
Legros, C.; and Guell, A. 1990. “Voice Analysis to Predict the Psychological or Physical State of a Speaker.”
Aviation, Space, and Environmental Medicine. Vol. 61. p. 266-71; Johannes, B.; Salnitski, V. P.; Gunga, H.;
and Kirsch, K. 2000. “Voice Stress Monitoring in Space—Possibilities and Limits.” Aviation, Space, and
Environmental Medicine. Vol. 71. p. A58-65; Brenner, M.; Doherty, E. T.; and Shipp, T. 1994. “Speech
Measures Indicating Workload Demand.” Aviation, Space, and Environmental Medicine. Vol. 65. p. 21-6;
Brenner, M.; Mayer, D.; and Cash, J. 1996. “Speech Analysis in Russia.” Methods and Metrics of Voice
Communications. Ed. B. G. Kanki and O. V. Prinzo. Department of Transportation, Federal Aviation
Administration, and Office of Aviation Medicine. DOT/FAA/AM-96/10. Washington, DC; and National
Transportation Safety Board. 1999. Uncontrolled Descent and Collision with Terrain, USAir Flight 427,
Boeing 737-300, N513AU, near Aliquippa, Pennsylvania, September 8, 1994. Aircraft Accident Report.
NTSB/AAR-99/01. Washington, DC.
51
For additional information, see NTSB/AAR-99/01.
NTSB/AAB-02/01
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