Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 143
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160 because the suspect valve left no physical evidence of a malfunction. In light of this evidence of
previous incidents and of the physical anomalies found in the Flight 990 wreckage, the NTSB’s
contention that there is no evidence of a possible mechanical malfunction is neither accurate nor
credible.
9.
(Page 23, footnote 40) The footnote refers to the February 2000 incident
involving an AeroMexico Boeing 767. The airplane experienced two failed bellcrank shear
rivets. This prompted a March 15, 2000, Boeing letter to Boeing 767 operators which discussed
the findings and explained that the bellcrank assembly rivets are designed to shear in the event of
a jam of a PCA. Efforts by the NTSB and the Egyptian Team to examine components of the
AeroMexico airplane were unsuccessful because the parts were not retained by Boeing.
Consequently, the statement that the “examination of the elevator PCA’s revealed no evidence of
a PCA jam” is an unsubstantiated report from Boeing -- which has its own interest in the
outcome of this investigation -- and was not verified by the NTSB. It would be helpful to
describe exactly what Boeing examined and what it observed rather than simply repeat the
conclusory statement that there was “no evidence of a PCA jam.” Moreover, the NTSB should
point out that the absence of evidence of a valve jam is not determinative as to whether or not a
jam occurred.
10.
(Page 25) There actually have been more than 152 reports of damaged shear
rivets. The draft report understates the magnitude of this issue and the safety implications of the
sheared rivets and the elevator control system failures.
11.
(Page 25) Given the critical nature of the bellcrank assembly rivet issue and its
possible involvement in the Flight 990 accident, it is irresponsible for the draft report to dismiss
this issue with nothing more than the statement that “although the cause of the bellcrank shear
rivet failures has not yet been determined, Boeing and the FAA are continuing to study the
failures to identify the cause.” What is not mentioned is that the FAA is discussing an elevator
system design change with Boeing. Given the documented safety problems with the elevator
control system and the ongoing, unresolved deficiencies, the dismissive treatment by the NTSB
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