Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 54
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160 48
the speedbrake…the aircraft would have pitched down at the same time.” The EgyptAir
submission further stated that the split elevators “do not support the conclusion that there
was a struggle in the cockpit” because (1) the CVR provides no indication of a struggle,
argument, or refusal to follow a command; (2) the FDR recorded control surface positions
but did not record the control column position or forces—“accordingly, one cannot
conclude from examining only the FDR data that pilot input to his control column caused
the elevators to be in a given position”; and (3) “at the same moment the elevators split,
both outboard ailerons moved upward…when this unusual aileron movement occurred
during the dive, the aircraft’s speed was approaching Mach 1.0, and no published
performance data is available to predict what will occur to ailerons at these high speeds. It
is likely, however, that aerodynamic shocks or flutter were occurring at the control
surfaces.”
In its submission, EgyptAir summarized its position as follows:
•
Accordingly, from an impartial review of the factual evidence gathered during
the investigation, it is clear that the [relief] first officer did not intentionally
dive the aircraft into the ocean.
•
At this point in the investigation considering the factual evidence gathered, it is
clear that the first officer did not commit suicide. Further investigation of the
elevator control system’s design in conjunction with the other factual
information available is necessary before a conclusion can be reached
regarding the true cause of this accident. Specifically, further engineering
analysis, including wind tunnel tests, is necessary to examine the dual actuator
malfunction in the speed ranges for which current data is not available. In
addition, further investigation of radar data is also necessary to completely rule
out the possibility of conflicting traffic. Until this work is accomplished, the
cause of this accident cannot be truly established.
•
An analysis of the facts and of the elevator control system’s design indicates
that malfunctions in two PCAs on the right elevator may have precipitated the
airplane’s dive. This dual PCA malfunction may have consisted of a latent or
nearly latent failure in one PCA that may have existed for a period of time
followed by a jam of a second PCA shortly before the dive.
•
The facts do not support the initial, and widely reported, theory that the [relief]
first officer deliberately dove the plane toward the ocean.
•
Without further information concerning the data from military and FAA radar,
one cannot rule out the possibility that the [relief] first officer may have been
attempting to avoid or maneuver the aircraft out of a perceived dangerous
situation at the time the dive occurred.
Boeing’s Submission
Boeing’s October 31, 2000, submission indicated that none of the mechanical
failure modes examined during the investigation were consistent with the FDR data
NTSB/AAB-02/01
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