August 27, 1998
January 9, 1997
Synopsis of video animation presented at the Board Meeting:
This video animation was derived from the last 2 1/2 minutes of the flight recorder data. The meteorological conditions that existed at the time of the accident are not depicted.
The animation starts with the airplane in a wings level attitude (autopilot engaged) at an altitude of approximately 6,000 feet just prior to the start of its descent to 4,000 feet. As the airplane approached 4,000 feet, ATC requested a right turn to a heading of 180° and a speed reduction to 150 knots. This was followed by right control wheel inputs and the airplane entered into a 26 ° right banked turn. After rolling out on a heading of 180°, the airspeed started to decrease from approximately 170 knots as the airplane began leveling off. While this was occurring, ATC requested a left turn to a heading of 090°
Just prior to leveling at 4,000 feet, a left banked turn was initiated with left control wheel inputs. Approximately 6 seconds after the start of the left turn, the control wheel values and bank angles began to diverge as the roll attitude reached approximately 22° left wing down.. At approximately the same time, the pitch trim and the control column began to move in the nose-up direction.
The engine torque values began to increase on both engines as the airspeed decreased to 148 knots. One second later the bank angle reached 30° left wing down and the torque values reach 33.3% (left engine.) and 39.3% (right engine).
At this point in the flight, the pitch attitude, which had been increasing steadily, started to decrease after reaching the peak of approximately 5° nose-up. However, the control column and pitch trim continued to move in a nose-up direction; a trend started 9 seconds earlier. The control wheel and rudder inputs continued to move in a right wing down direction as the bank angle increased to 38° left wing down. Engine torque increased to 85.2% (left engine.) and 94.7% (right engine) and the airplane continued to decelerate reaching an airspeed of 147 knots.
The CVR recorded the captain stating "looks like your low speed indicator" which was followed by an abruptly increase in engine torque to 103.5% (left engine) and 96.1% (right engine) as the airspeed decrease to 146 knots.
Within the a one second period, the autopilot status changed from "engaged" to "disengaged", the control wheel position changed 25.8°, from 19.5° right wing down to -6.3° left wing down, the roll attitude changed 11° (- 40° to -51°) in 0.5 seconds, and the pitch attitude decreased 3°( 3° to 0.0°) in 0.25 seconds. The pitch attitude continued the nose-down trend, decreasing to 50° nose-down within five seconds. The abrupt left roll also continued, reaching 146° left wing down within two seconds. This was followed by left and right roll oscillations in excess of 120°, and nose-down pitch oscillations between 80° and 20°. The peak torque values of 108% (left engine) and 138% (right engine) occurred shortly after the autopilot disconnected. These peak values were present for less than a second, and over the next 4 seconds, were reduced to near flight idle. The altitude data indicated a rapid descent from 4,000 feet down to approximately 800 feet. The CVR recorded the sound of the "stick shaker" shortly after the autopilot disconnected. Except for a brief interruption, the "stick shaker" remained on until the end of the recordings.