- 55 -
2.16.7
Even with the above failures, the pitch control that should have been available still exceeded that evident from the DFDR data. The aircraft's manufacturer found that a reduction in aerodynamic effectiveness of the left inboard elevator to at least half its normal value would have been required in order for their simulation to match the measured response. It was presumed that this had occurred due to surrounding structural damage.
2.16.8
In summary, it was evident that within a second or two of the first signs of a missile attack, the aircraft suffered the following damage:
2.16.9
a) failure of a rudder control cable or one of its attachments;
b) failure of a cross-over cable between the left inboard and right outboard elevators;
c) damage to the synchro monitoring the stabilizer angle for the DFDR that was mounted just aft of the stabilizer centre box or of its mechanical installation or wiring;
d) failure of hydraulic systems No. 1, 2 and 3;
e) structural damage in the region of the left inboard elevator that significantly reduced
its aerodynamic effectiveness; and
f) puncturing of the pressure cabin with holes in the order of 1.75 sq.ft.
Although other alternatives were possible in view of the fact that two missiles were involved and reported to have exploded near the aircraft, all of the above damage could be associated with damage inflicted by a missile in the area of the stabilizer centre section. The rear pressure bulkhead was only about 7 ft ahead of that area.
2.16.10
From seventeen to forty seconds after the initial attack, the aircraft continued to climb. and reached a maximum altitude of 38 250 ft with a reduction in calibrated airspeed from the initial 286 kt to 220 kt. From this combination of altitude and airspeed, estimates made by the aircraft's manufacturer indicated that all four engines must still have been functioning normally. The flight engineer also twice stated that the engines were normal. This suggested that the infra-red guidance missile had not homed directly onto an engine.
2.16.11
After the aircraft started to descend and at the time of temporary recovery to about level flight, there were also significant fluctuations in the lateral acceleration that is a measure of the lateral aerodynamic force on the aircraft. This was probably indicative of a premature fin stall. At the time that the buffet commenced, the aircraft was still in a left turn but with a bank angle less than that normally required for zero sideslip; therefore, it would have been slipping out of the turn. The stall could have been aggravated by external damage to the fin or to the rudder mechanism.
2.16.12
It could not be established why both flight recorders simultaneously ceased to operate 104 seconds after the attack. The power supply cables were fed to the rear of the aircraft in raceways on opposite sides of the fuselage until they came together behind the two recorders.