Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 66

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sound similar to [the] electric seat motor operating.” Because the relief first officer’s seat
was likely moved into an aft position because the command first officer had vacated the
seat, and in light of the autopilot disconnect and subsequent flight control movements, the
whirring sound is consistent with the relief first officer moving his seat forward into a
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position from which he could manually fly the airplane.
Thus, all manual flight control
inputs made after 0148:19, until the command captain’s return to the cockpit at 0150:06,
must have been made by the relief first officer.
The absence of an autopilot disconnect warning tone on the CVR recording when
the autopilot disconnected at 0149:45 is consistent with the autopilot being manually
disconnected by rapidly double-clicking on the control yoke-mounted autopilot
disconnect switch. Because the relief first officer was alone in the cockpit, the evidence
indicates that he manually disconnected the autopilot. The Safety Board’s examination
revealed no evidence in the CVR, FDR, ATC, or radar data of any system malfunction,
conflicting air traffic, or other event that might have prompted the relief first officer to
disconnect the autopilot; therefore, there was no logical operational reason for the relief
first officer to disconnect the autopilot while in cruise flight over the ocean. Further, as
previously stated, the Board’s testing and evaluation of the 767 elevator system showed
that none of the failure modes examined during this investigation would have resulted in
control column movements without concurrent identifiable movements of the elevators,
which would have been observed in the FDR data. The FDR did not record any unusual or
alarming elevator movements before the autopilot was disconnected; therefore, it is
unlikely that the relief first officer was prompted to disconnect the autopilot because he
sensed unusual control column movements.
Aside from some very slight elevator movements and a very gradual left roll, the
airplane remained in level flight at flight level 330 for about 8 seconds after the autopilot
was disconnected. As previously discussed in the section titled, “767 Autopilot
Information,” such slight movements are normal and expected when the autopilot is
disengaged and the pilot takes manual control of the airplane. There was no indication of
an upset or loss of control at this time.
At 0149:48, the relief first officer again quietly stated, “I rely on God.”
At 0149:53, the throttle levers were retarded (moved from their cruise power setting to
idle). This throttle lever movement occurred at a rate that was more than twice that which
the autothrottle can command. Further, the throttle levers moved 10º to 15º beyond the
minimum position that the autothrottle would have been able to command at the existing
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flight conditions to the throttle levers’ full aft idle stop, about 33º.
Movement of the
throttles aft of the autothrottle commanded position requires a manually applied force of
about 9 pounds on the throttle levers to override the autothrottle servomotor clutch. Thus,
it is apparent that the throttle lever movements at 0149:53 were caused by the relief first
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officer’s manual inputs and were not the result of autothrottle commands.
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This electric seat motor sound was recorded by both the CAM and the hot microphone at the first
officer’s position, further confirming that this sound represented a motion of the relief first officer’s seat.
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This throttle lever position was consistent with manually input throttle lever positions recorded by the
FDR earlier in the accident flight.
NTSB/AAB-02/01

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