Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 59
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160 53
anomaly), he told investigators that the airplane was “almost perfect.” No autopilot
difficulties were reported by the flight crew that flew the airplane from LAX to John F.
Kennedy International Airport (JFK), New York, New York, immediately before the
accident flight nor did they report any autopilot anomalies in the airplane’s maintenance
logbooks. Further, the Board’s examination of the FDR data before and after all recorded
autopilot disconnects in the 25 hours of data recorded by the FDR (including the accident
flight) revealed no evidence of abnormal autopilot or elevator surface behavior.
The Safety Board’s review of ATC, FDR, CVR, and radar information indicated
that the airplane’s movements during the accident flight were routine until about 0149:54
(9 seconds after the autopilot disconnect occurred), when an abrupt sustained nose-down
elevator motion occurred. A review of the FDR data indicated that the accident airplane’s
pitch motion before and during the accident sequence was consistent with the elevators’
recorded movements. Boeing’s full-flight engineering simulator was used to evaluate the
consistency of the elevator positions with the pitch motions recorded on the FDR. During
these evaluations, the elevator movements required to make the simulator duplicate the
pitch motions recorded by the accident airplane’s FDR and the flightpath developed from
the available data closely matched the elevator movements recorded by the FDR. Further,
the recorded load factors were consistent with the recorded movements of both elevator
surfaces throughout the recorded data, even during the time that the data indicated a split
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between the left and right elevator surfaces (see figure 4).
The results of the Safety Board’s examination of CVR, FDR, radar, airplane
maintenance history, wreckage, trajectory study, and debris field information were not
consistent with any portion of the airplane (including any part of the longitudinal flight
controls) separating throughout the initial dive and subsequent climb to about 25,000 feet
mean sea level (msl). It is apparent that the left engine and some small pieces of wreckage
separated from the airplane at some point before water impact because they were located
in the western debris field about 1,200 feet from the eastern debris field. Although no
radar or FDR data indicated exactly when (at what altitude) the separation occurred, on the
basis of aerodynamic evidence and the proximity of the two debris fields, it is apparent
that the airplane remained intact until sometime during its final descent. Further, it is
apparent that while the recorders were operating, both elevator surfaces were intact,
attached to the airplane, and placed in the positions recorded by the FDR data and that the
elevator movements were driving the airplane pitch motion, and all associated recorded
parameters changed accordingly.
Mechanical Failure/Anomaly Scenarios
The Safety Board evaluated possible mechanical failure and pilot action scenarios
in an attempt to determine whether they were consistent with the elevator movements
made during the accident sequence. As previously discussed in the section titled,
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The engineering simulator was modified to model the left and right elevator surfaces independently,
and, using split elevator movements similar to those recorded on the FDR, the simulator was able to
duplicate the FDR-recorded pitch history.
NTSB/AAB-02/01
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