Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 55
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160 49
because (1) “the FDR elevator positions did not displace to the positions [predicted by the
failure mode and effects analysis] during the initial pitchover” and (2) “the elevator
motions after the initial pitchover indicate that both surfaces were functioning normally.”
Boeing also considered several operational scenarios, including collision
avoidance, rapid descents, response to engine oil pressure lights, and loss of thrust on both
engines. Boeing’s submission stated that, “EgyptAir 990 crew actions were determined to
be inconsistent with the performance of standard Boeing recommended operating
procedures and training for the 767 airplane.”
In its submission, Boeing summarized its position as follows:
•
Flight control surface movements recorded on the [FDR] are capable of
generating the airplane flight path recorded by the [FDR] and radar.
•
Based on the examination of the recovered wreckage, Boeing did not find any
evidence of a failure condition within the airplane flight control system that
could have caused or contributed to the initial pitchover, or prevented recovery
from the dive.
•
Boeing participated in examining all potential failure conditions developed
during the investigation and could not find a failure condition that: (1) matched
the data recorded by the [FDR] or (2) resulted in a condition that was not
recoverable by the pilot.
•
Therefore, Boeing does not believe that the loss of EgyptAir 990 was the result
of a mechanical failure of the aircraft or aircraft systems.
EgyptAir’s January 12, 2001, Response to Boeing’s Submission
In its January 12, 2001, response to Boeing’s submission, EgyptAir stated that
Boeing did not “account for or…comment on” the FAA’s ADs regarding bellcrank shear
rivet failures in its submission. However, EgyptAir’s response to Boeing’s submission
indicated that it could not determine whether the bellcrank shear rivet failures were
involved in the accident, “[the FDR data were] remarkably consistent with test data of a
jam of two right elevator servos in the trailing edge down position.” EgyptAir further
stated that “the differences between the test data and the FDR can be adequately explained
as either performance variances within normal limit or limitations of the test facilities and
protocols.”
Additionally, EgyptAir’s response to Boeing’s submission indicated that there was
evidence of a mechanical malfunction of the elevator system; specifically, EgyptAir cited
the reported autopilot difficulties during an approach to LAX the day before the accident
and the downward elevator deflections recorded by the FDR at autopilot disconnect.
EgyptAir stated the following:
[This evidence] shows that an anomaly existed in the flight 990 elevator system
even before the aircraft left New York for Cairo on October 31, 1999—a latent
NTSB/AAB-02/01
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