Aircraft Accident Brief Ntsb/aab-02/01 (Pb2002-910401): Egypt Air Flight 990, Boeing 767-366er, Su-Gap - National Transportation Safety Board Page 15
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configured to seat a maximum of 10 first-class, 22 business-class, and 185 economy-class
passengers and to carry cargo.
The accident airplane was equipped with two P&W 4060 turbofan engines.
Company maintenance records indicated that the No. 1 (left) engine, S/N 724126, was
installed on the accident airplane on April 19, 1998, and had operated about 25,708 hours
since new and that the No. 2 (right) engine, S/N 724127, was installed on the accident
airplane on June 3, 1998, and had operated about 19,316 hours since new.
767 Longitudinal Control System Information
Because the accident sequence involved a sustained unusual motion about the
airplane’s pitch axis, the Safety Board examined the 767’s longitudinal flight control
system. According to the Boeing 767 Maintenance Manual, the 767’s longitudinal flight
control system includes two (left and right) sets of linked elevator surfaces (inboard and
outboard), which are attached to the rear spar of the movable horizontal stabilizer by
hinges. Each outboard elevator surface is driven by three power control actuators (PCA).
Because the outboard and inboard surfaces are linked, the inboard elevator surfaces move
when the outboard elevator surfaces are driven. Hydraulic power for elevator PCA
movement is provided by the 767’s three independent hydraulic systems—each hydraulic
system powers one of each elevator surface’s PCAs, which provides redundancy within
the elevator control system. (Components in the elevator control system are shown in
figures 1a and 1b.)
Two parallel sets (one operated from the captain’s side, the other from the first
officer’s side) of flight control components move the elevator surfaces. Control column
inputs made at the captain’s position are linked directly to the actuators for the left
elevator surface, whereas control column inputs made at the first officer’s position are
linked directly to the actuators for the right elevator surfaces. The two parallel sets of
flight control components are linked together at the forward and aft override
mechanisms/linkages and slave cable interconnects. Flight control commands from the
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captain’s and first officer’s control columns are transmitted through linkages and cables
from the front of the airplane to the left and right aft quadrant assemblies, respectively.
The aft quadrant assemblies then translate the inputs to the respective bellcrank
assemblies and the input control rods for each of the three elevator PCAs for each
outboard elevator surface.
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A flight cycle is one complete takeoff and landing sequence.
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The cables for the captain’s (left-side) system are routed below the floor boards, and the cables for the
first officer’s (right-side) system are routed above the cabin ceiling.
NTSB/AAB-02/01
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