Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 56

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defect that could not be detected by the crew. In light of these facts, it is plausible
to believe that—just as [the captain of the flight into LAX] had done a day
earlier—the [relief] first officer on flight 990 disconnected the autopilot after
observing some unusual movement of the column.
The EgyptAir response to Boeing’s submission also stated that examination of the
recovered wreckage “indicated damage to the elevator system prior to impact.”
Specifically, EgyptAir asserted that the damage to the right outboard PCA (sheared pin
and improperly positioned bias spring) and right elevator bellcrank shear rivets (failed in
opposite directions) likely occurred before the airplane impacted the ocean.
Further, in its response to Boeing’s submission, EgyptAir reiterated its position
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that its analysis of the elevator’s motions
indicated that the elevator split observed in the
FDR data was not the result of a struggle between the captain and the relief first officer.
The response stated that the split “may [have been] the result of the loss of the right
elevator.” To support this statement, EgyptAir asserted that (1) there was no indication on
the CVR transcript that a struggle occurred in the cockpit; (2) the uncommanded elevator
positions might have resulted from unique aerodynamic phenomena as the airplane’s
speed increased; (3) when an FDR records elevator position, it is actually recording the
sensor position, which does not, by itself, indicate the position of the elevator or the
control column; and (4) the pitch and roll motions recorded during the last 15 seconds of
FDR operation were “much closer to the expected aircraft performance if the right
elevator is missing.”
EgyptAir’s response to Boeing’s submission also stated the following:
EgyptAir has determined that the FDR flight profile after the split is consistent
with the expected aircraft performance only if the right elevator has departed the
airplane….this conclusion is based upon the absence of expected rolling moment
that would have been induced by a differential deflection of the elevators…shown
on the FDR.
In addition, EgyptAir’s response stated the following:
Boeing’s engineering simulator did not provide an accurate model of real
aircraft performance.
Boeing often ignored the more reliable ground test results.
Boeing’s selective use of test data resulted in inconsistent conclusions.
Boeing’s conclusions regarding crew actions are erroneous.
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For its analysis of the elevator motions, EgyptAir used the methods of Roskam (Airplane Design,
Part VI, Roskam Aviation and Engineering Corporation).
NTSB/AAB-02/01

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