Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 147
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160 caused by a high-speed impact. In fact, the fractures are stress fractures that are just as
consistent with low-speed forces as with high speed. This statement in the report needs to be
corrected.
20.
(Page 41) The NTSB states that the U.S. Air Force determined that unidentified
radar returns “were caused by radio interference.” For over 18 months, the Egyptian Team has
been seeking the technical data that would either support or refute this conclusion and has
consistently been refused access to this information. The data on which the Air Force relies
should be disclosed and delivered to the Egyptian Team.
21.
(Page 44, footnote 70) This note suggests that even a small sideslip angle or roll
rate could produce large changes in the aerodynamic forces acting on the ailerons when
approaching 1.0 Mach. If the NTSB believes that these same forces do not affect the elevators in
a similar way, the difference must be explained.
22.
(Page 45, footnote 71) The NTSB advises that for performance numbers higher
than .91 Mach (the highest number for which Boeing has verified data), “the simulator’s
database was adjusted to reflect extrapolations . . . .” This reflects the inexact methodology
relied upon by the NTSB to arrive at its conclusions. With respect to the use of extrapolated data
to predict transonic airplane performance, the Egyptian Team is not aware of any study or
analysis that validates this approach. The reason is that airplane performance and aerodynamic
forces change in radical ways as the airplane’s speed approaches 1.0 Mach as it did here.
Consequently, without technical evidence that extrapolation produces valid results, none of the
simulator results above .91 Mach can be considered reliable.
Furthermore, the validity of many of the simulator results is questionable for an even
more fundamental reason. The simulator runs were based on published Boeing performance data
and predictions. Various ground tests, using an actual Boeing 767, however, demonstrated that
many of Boeing’s predicted results did not reflect real-world airplane behavior. Nevertheless,
Boeing refused to use the ground test results in the simulator experiments. Thus, there is
empirical evidence that demonstrates the inherent unreliability of conclusions based solely on
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