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Tape reduction data show that the first indications of other than normal flight began about 15 seconds before impact. At this time the aircraft was pushed over and rolled into a left bank. It was time to commence a left turn to the final approach and the increasing compass heading, due to gyro gimbal error, shows the roll which was also verified by witnesses.
At this point the aircraft yawed rapidly to the right. The yaw angle has been estimated as high as 17 degrees, which is well beyond the 11- to 14-degree angle that can be successfully controlled with full opposite use of the lateral control devices. The crew for some unknown reason, failed to recognize and correct the development of this yaw and the aircraft continued to roll to the right.
When the aircraft passed the 90-degree bank position, it was yawed right approximately 20 degrees, resulting in approximately a 30-degree nosedown attitude. The yaw was at its maximum angle and the roll rate had reached approximately 40 degrees per second.
As the aircraft passed the inverted position the yaw angle was reduced considerably, indicating that some corrective action had been taken in the form of advancing the thrust levers on Nos. 3 and 4 engines and applying full left rudder and aileron. Positive acceleration was held at 1—1/2 to 1-3/4 g.
As the aircraft passed the 270-degree roll position it was in a zero yaw condition. Acceleration was held at approximately 2 g, which is in the buffet range and is the tightest pullout that the aircraft could make. The power was then nearly symmetrical.
The aircraft struck the ground in a nearly wings-level attitude, yawed to the left approximately 12 degrees, with considerable and nearly symmetrical power. The attitude was approximately 12 degrees nosedown but the angle of impact was approximately 26 degrees, giving a floorline angle of attack of 14 degrees. The yaw and nearly stalled condition indicated on the flight recorder trace were verified by the ground impact marks at the crash site.
There was no control or actuator position by which power being produced at impact could be determined. The energy expended in halting rotation of the engines, as evidenced by the extent of damage from rotational interference, was the primary means of determining the approximate power at impact. Rotational damage indicated all engines were producing appreciable power at impact. Unstacking of the N1 compressors of Nos. 3 and 4 engines suggests slightly more power was being produced by these engines than Nos. 1 and 2. However, the readings of the four oil temperature gages indicated more power was being produced by Nos. 1 and 2 engines than by Nos. 3 and 4. This apparent conflict of factual evidence would be logical if, at the start of loss of control, while operating with Nos. 3 and 4 engines reduced to idle thrust their power levers were advanced, quickly to the full-thrust position. The higher power established by advancing the thrust levers would not be reflected on the oil temperature gages during the elapsed time to ground contact. In view of the relatively low altitude as which control was lost, it is concluded that this sequence of events occurred.
Another factor in this accident was the delay in acceleration time of jet engines after thrust lever advancement. The delay in engine acceleration from
