Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 149
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160 these inaccuracies do not support a definitive conclusion as to the amount of elevator deflection
in the various failure scenarios. The degree of precision represented in the NTSB draft report is
simply not a valid product of the simulator testing and misrepresents the reliability of the data
obtained.
25.
(Page 50) The NTSB acknowledges that in recovering the airplane during the
dive, “additional forces” would be required beyond those necessary for recovery if a failure had
not occurred. However, the NTSB omits any discussion the magnitude of those “additional
forces” and of the impact that such forces have in the recovery of the airplane. Again, there was
a marked difference in the additional forces demonstrated through ground testing and those
predicted in the simulator -- with the ground testing forces being much higher. The actual
demonstrated forces were never used in the simulator, making the NTSB’s comments concerning
recoverability speculative. Rather than simply identify an issue and then ignore it, the NTSB
must discuss the additional forces needed for recovery, the duration that such forces must be
applied, and the effect of zero or negative g on the crew’s ability to apply such forces. Unless
these issues are fully developed, there can be no meaningful conclusion regarding the
recoverability of the airplane.
The numerous references in the draft report to the recoverability of the airplane reveal
another “backdoor” through which the NTSB arrives at its probable cause determination.
Presumably, the NTSB’s logic is that if an airplane suffering a dual PCA jam can be recovered in
the simulator, then the failure to recover Flight 990 means that it did not experience a dual PCA
jam. The obvious flaw in this logic is that no matter how good the simulator is, it cannot
reproduce the feelings, sensations, and emotions triggered by an unexpected upset, at night, over
the ocean, during which the airplane and its contents experience a 40 degree nose down pitch and
the crew and passengers experience negative g forces.
Further, in none of its references to “recoverability” does the NTSB ever define what it
means by that term. If recovery were defined as a point at which an uncommanded descent has
been arrested, the wings are level, and the pitch has almost reached zero, then the Flight 990
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