Descent and Communication Issues
The twin-turbojet, transport-category airplane was destroyed when it departed controlled flight during descent into its final destination and impacted terrain. The flight crew received clearance to descend from FL 390 to 10,000 feet and established a descent rate of 4,000 feet per minute. As the airplane descended through FL 219, air traffic control requested that the pilot contact approach control. The pilot read back an incorrect frequency and spoke an unintelligible word. The controller attempted to correct the pilot, but no additional communications were received from the flight crew.
A 1680 Hz frequency tone lasting 0.1 seconds was identified within a pause in the pilot's last transmission. Only two systems on the airplane have aural warnings within that frequency range: the cabin altitude warning and the overspeed warning. Both systems were destroyed during the accident sequence.
Loss of Control and Radar Data
Shortly after the final transmission from the pilot, radar data depicted the airplane climbing back to FL 231 before entering a steep and rapid descent. A performance study indicated that just prior to the loss of control, the airplane exceeded its maximum operating airspeed of 300 knots calibrated. However, according to the manufacturer, the airplane had been successfully flown at airspeeds up to 400 knots calibrated without loss of control.
Structural Findings
The right wing and sections of the right horizontal stabilizer and elevator separated from the airplane just prior to impact with terrain. These components were located approximately 200 to 250 feet from the main impact crater.
Investigation Findings
No anomalies with the airframe or engine were found that would have led to the loss of control. A cockpit voice recorder was installed in the accident airplane, but it did not record the accident flight.