Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 44
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160 38
•
At 0150:08, as the airplane passed through about 30,800 feet msl, the airplane
exceeded its maximum operating airspeed (0.86 Mach), and the Master
Warning alarm sounded. The maximum rate of descent recorded during the
dive was about 39,000 fpm at 0150:19, as the airplane descended through
about 24,600 feet msl. At 0150:23, the airspeed reached its peak calculated
value of 0.99 Mach, as the airplane descended through about 22,200 feet msl.
•
At 0150:15 and about 27,300 feet msl, the left and right elevator surfaces
started to move slowly (about 0.6º per second) in the trailing-edge-up (TEU)
direction, back toward their neutral position. The pitch angle, angle of attack,
and load factor also started to increase at this point, so that when the FDR
recorded the last data for the accident flight at 0150:36.64, the pitch angle had
increased to about 8º nose down, and the airplane was experiencing about
2.4 Gs.
•
Between 0150:18 and 0150:27, the FDR recorded TEU movements of the left
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and right outboard ailerons and the left inboard aileron.
•
At 0150:21, the left and right elevator surfaces started to split (that is, to move
asymmetrically). The right elevator surface started to move TED, whereas the
left elevator surface moved TEU. This split between the left and right elevator
surface positions continued to the end of the FDR data, varying in magnitude
but averaging about 4º difference between the surfaces (see figure 2).
•
Between 0150:21 and 0150:23, the engine start lever switches for both engines
moved from the run to the cutoff position.
•
Between 0150:24 and 0150:25, both throttle handles moved full forward.
•
Between 0150:25 and 0150:26, the speedbrake handle moved to its fully
deployed position. Coincident with this activity, between 0150:24 and
0150:27, the left elevator surface moved briefly in the TED direction (from
3º TEU to 1º TEU) before it returned to 3º TEU.
•
Almost immediately after the speedbrakes were deployed at 0150:26, the left
elevator surface deflection increased further, reaching its maximum deflection
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of more than 3.8º nose up about 0150:30.
After 0150:30, the left elevator’s
nose-up deflection gradually reduced, until the data for that parameter ended at
0150:36 with a left elevator deflection of about 2.3º nose up.
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The Safety Board’s examination of Boeing’s 767 certification flight test data revealed that the low oil
pressure warnings for P&W 4060 engines would occur when the engine’s oil pressure drops below 70 lbs
per square inch, as occurred when the accident airplane was operating at low (near 0) load factors. (For
additional information, see Powerplants Group Chairman’s Factual Report and appendixes 1 through 8.)
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According to Boeing, these movements were consistent with the effects of blowdown on those
surfaces as documented during flight tests. However, the outboard aileron split recorded by the FDR after
about 0150:27, which is discussed later in this section, was not consistent with the flight test data.
67
As previously discussed, Safety Board simulations demonstrated that a pilot in the left seat could have
moved his right hand from the control wheel to the throttle, advanced the throttles, moved his hand a little to
the left, and deployed the speedbrakes in the 3 to 4 seconds it took for these events to occur.
NTSB/AAB-02/01
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