What happened
On March 1, an international passenger flight operated by TAROM, traveling from Chicago to Amsterdam, experienced a significant flight upset near Rivière-du-Loup, Quebec. While cruising at FL330 at Mach 0.83, the aircraft's autopilot disengaged. Immediately following the disconnect, the Airbus A310-325 experienced a rapid pitch-up, reaching a maximum pitch angle of nearly 30 degrees and a vertical acceleration of 1.94 g.
The aircraft climbed sharply to FL385, with the rate of climb exceeding 12,000 feet per minute, while the airspeed dropped to a minimum of 155 knots. During this maneuver, the crew experienced four separate stall warning events. The aircraft then entered a rapid descent, dropping to FL315, before a subsequent climb was moderated after the crew successfully re-engaged autopilot 1. The flight eventually stabilized at FL350 and continued to its destination without further incident or damage to the aircraft. There were no injuries among the 80 passengers and 14 crew members.
The investigation
The investigation focused on the mechanical failure that triggered the sudden pitch-up and the crew's subsequent handling of the aircraft. Investigators examined the aircraft's flight control systems, specifically the elevator servo and horizontal stabilizer trim. The investigation also reviewed maintenance records regarding a recent rigging check performed on the autopilot elevator servo.
Findings
- The primary cause of the flight upset was a misrigged autopilot elevator servo control, which induced an initial pitch-up moment upon autopilot disengagement.
- The crew's pitch control inputs were ineffective or inappropriate at certain stages, which contributed to the aircraft entering a stall regime.
- An aft center of gravity position, caused by a fault in the CGCC system, acted as a contributing factor.
- The aircraft's high cruise speed also contributed to the severity of the upset.
- The misrigging was likely due to the use of an incorrect or improperly inserted rigging pin during a maintenance check performed two months prior.
- The maintenance manual at the time specified an inappropriate rigging pin size, a discrepancy that had been previously identified by the manufacturer.