Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 45
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160 39
•
Between 0150:21 and 0150:24, the right elevator surface’s nose-down
deflection increased gradually, then increased rapidly until just after 0150:25,
when the nose-down deflection briefly reduced from about 2.35º to about 1.9º
nose down. Between 0150:21 and 0150:23, the engine start levers moved to the
cutoff position. At 0150:26, the right elevator’s nose-down deflection began to
increase again, reaching its maximum nose-down deflection of about 3.2º at
0150:29. Subsequently, the right elevator’s deflection moved generally toward
a nose-up position, with occasional movements in a nose-down direction;
when the FDR data ended, the right elevator deflection was 0.2º nose down.
•
Between 0150:27 and 0150:32, the FDR recorded a split condition in the
outboard ailerons (the left outboard aileron maintained its approximate presplit
68
deflection, while the right outboard aileron began to move in a TED direction).
The outboard ailerons had been moving in a TEU direction since 0150:18.
•
During the elevator split, the larger movements of the left and right elevators
individually corresponded with changes in the load factor (see figure 4). For
example, between 0150:30 and 0150:36, the recorded movements of the right
elevator (lower graph) are reflected in the load factor profile (upper graph).
•
No secondary radar returns were received from the accident airplane after the
last data were recorded by the FDR at 0150:36.64.
•
Performance calculations based on primary radar returns indicated that the
airplane’s rapid descent stopped at an altitude of about 16,000 feet msl. The
primary radar returns indicated that the airplane then began to climb, reaching
about 25,000 feet msl about 0151:15. During this climb, the airplane’s heading
changed from about 80º to about 140º.
•
After 0151:15, the data indicated that the airplane began a second rapid descent
that continued until it impacted the ocean.
Seven primary radar returns from the airplane were recorded during the second
dive; the altitude estimates from these returns are subject to potentially large errors, which
introduces significant uncertainty into the performance calculations during the second
dive. However, the data indicate that the airplane impacted the ocean about 0152:30, with
an average descent rate during the second dive of about 20,000 fpm.
68
Wind tunnel tests and computational fluid dynamics analyses show that a small sideslip angle and/or
roll rate could produce large changes in the aerodynamic forces acting on the outboard ailerons at speeds
approaching Mach 1.0, but these forces would not likely be strong enough to cause the split elevator
condition recorded by the accident airplane’s FDR. For additional information, see Aircraft Performance –
Addendum #1.1, Addendum to Group Chairman’s Aircraft Performance Study, including appendixes B and
C (correspondence from Boeing, dated April 12 and 16, 2001).
NTSB/AAB-02/01
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