What happened
On 23 December 2010, at 16:10 UTC, a Bombardier BD–100–1A10 Challenger 300, registration OH-FLM, experienced a sudden in-flight pitch upset while climbing near the Moscow Terminal Control Area. The aircraft was operating a flight from Moscow to St. Petersburg. The flight was a familiarization flight for the co-pilot, who was designated as the pilot flying for the duration of the mission.
During the initial climb, the Engine Indication and Crew Alerting System (EICAS) issued an autopilot stabilizer trim failure warning. Following the established fault checklists, the captain disengaged the autopilot. This action triggered a series of pitch oscillations, specifically a nose-up and nose-down motion, which the crew eventually stabilized. The aircraft subsequently returned to Sheremetyevo Airport. The incident resulted in two injuries to passengers and damage to the cabin interior. The injured passengers were transported to a hospital in Moscow.
The investigation
The investigation focused on the sequence of events following the autopilot disengagement and the adequacy of the aircraft's checklists. Investigators examined the crew's handling of the failure and the technical characteristics of the aircraft's flight control systems. The inquiry also reviewed the crew's training, cockpit coordination, and the specific instructions contained within the aircraft's checklists regarding manual flight transitions.
Findings
The primary cause of the upset was the overcontrolling of the aircraft's pitch attitude immediately after the autopilot was disengaged.
Several contributing factors were identified:
- The flight crew lacked sufficient knowledge regarding the operating principles and characteristics of the aircraft's artificial pitch feel system, as well as deficiencies in their specific system training.
- There were notable shortcomings in the crew's pre-flight checks and cockpit coordination during the flight.
- The aircraft's checklists instructed the pilots to grip the control column firmly before disengaging the autopilot, but failed to instruct them to adjust the airspeed to match the horizontal stabilizer's position.
- The checklists did not include a requirement to activate the 'Fasten Seat Belt' sign prior to the event.
- The high airspeed at the time of the occurrence contributed to the significant G-forces experienced during the pitch oscillations.