Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 153
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160 there was no physical evidence observed on the PCA’s of the USAir Flight 427 or United Flight
585 where the NTSB concluded that the PCA caused a malfunction of the rudder. In the
EgyptAir accident, the NTSB has physical evidence of an anomaly with the PCA yet concludes
that “… the absence or presence of a jammed or disconnected impact linkage or a jam in the
servo valve in one of the airplanes elevator PCA’s could not be established.”
33.
(Page 64) The centerpiece of the NTSB’s argument that there was no evidence of
a mechanical failure is that the elevators did not move to 6? TED at the beginning of the dive. As
discussed previously, there are substantial reasons to question whether the calculated -- not
demonstrated -- value of 6 degrees is accurate. Moreover, there is no discussion of whether this
initial deflection value could be less if the crew were exerting back-pressure on the control
column or if the failure were intermittent -- or at least not total -- at the beginning of the dive.
Finally, there is no data in the docket showing the range of deflection that could be expected in
the case of a dual PCA jam. Because the 6 degrees is a calculated number, it does not reflect
real-world variances. If such variances were accounted for, the deflections observed on the
Flight 990 FDR would likely be far closer to the NTSB’s calculations for a dual PCA jam.
Again, the NTSB’s emphasis on the precise amount of deflection is misleading, not only because
the testing did not validate that degree of precision, but also because it tends to obscure the
physical evidence of a possible jam -- the oppositely sheared rivets, the sheared servo slide pin,
and the differential bending in the PCA connecting rods. This physical evidence cannot be
dismissed as impact damage when there is no evidence to prove it was impact-related.
34.
(Page 65) Figure 2 shows a close correlation during the first 13 seconds between
the accident aircraft FDR elevator profile and the dual jam failure scenario. Figure 2 also shows
a close correlation between the accident aircraft elevator profile and all three failure scenarios if
the RFO makes some limited control inputs once the accident sequence starts. However, the
draft report does not address these issues and simply dismisses the possibility that any of the
failure scenarios are consistent with the accident aircraft FDR data. Again, the NTSB’s failure to
include any discussion of the forces necessary to move the flight control surfaces creates a
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