Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 122
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160 A second example of the NTSB’s limited investigation was its reluctance to conduct
comprehensive aircraft performance testing in the flight simulators at Boeing. The superficial
level of the first simulator tests led to further testing, but only at the insistence of the Egyptian
Team. As late as March 2001, a new series of simulator tests was scheduled by the NTSB to
resolve selected technical questions. Even after these latest tests, many issues remain concerning
the validity of the simulator tests.
Another example was the NTSB’s continuous refusal to conduct any analysis or tests
concerning the recorded behavior of the ailerons of the accident aircraft. This was despite the
FDR data which showed that Flight 990, while seemingly under control and in the process of
recovery from the initial steep dive, suddenly experienced “split” elevators and abnormal aileron
movements. The NTSB theorized that the abnormal aileron movement was caused by shock
waves or other extraordinary aerodynamic phenomena as the airplane approached the speed of
sound. However, the NTSB refused to consider these same shock waves as the possible
explanation for the FDR data showing a “split” in the elevators. Instead, with no proof
whatsoever, the NTSB concluded that the split of the elevator surfaces was due to opposite
control forces in the cockpit – in other words, a fight between the Captain and the relief First
Officer for control of the airplane. Although there was no evidence of a struggle, the NTSB used
the elevator data to support its deliberate act scenario -- while, at the same time, it ignored any
serious investigation of the unexplained behavior of the ailerons.
Along these same lines, the Egyptian Team continually requested that the NTSB and
Boeing perform wind tunnel tests on the Boeing 767 flight control systems at the same speeds
experienced by Flight 990 -- up to .99 Mach. There is no validated Boeing data on the 767
airplane above .91 Mach; consequently, any conclusions about the performance of the airplane at
higher speeds are necessarily based upon the extrapolation of .91 Mach data -- an extremely
speculative technique when dealing with transonic speeds. The requests for wind tunnel testing
to obtain accurate performance data were denied. Consequently, a thorough aircraft performance
analysis to explain the meaning of the FDR data and the forces working on the airplane has not
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