Incident Overview
During a flight from Red Lake, Ontario, to Winnipeg, Manitoba, a Fairchild Metro 23 (serial number CC829B) operating as Bearskin Lake Air Service Flight 317 encountered a severe flight anomaly. The aircraft was descending at approximately 4,600 feet above sea level when it suddenly pitched up without crew input. The uncommanded maneuver resulted in a rapid climb to nearly 7,000 feet with a peak pitch attitude of 52 degrees nose-up.
Crew Response and Landing
The first officer, who was at the controls, immediately pushed forward on the yoke to counteract the nose-up force. The airspeed dropped below 40 knots indicated airspeed, triggering stall warnings. Both crew members worked together to push the nose down, eventually stabilizing the aircraft at 6,000 feet and 140 knots. Due to increased control forces required with flaps extended, the captain elected to perform a flapless approach. The first officer exerted full forward pressure on the control column using both hands and feet to maintain the nose-down attitude during the final approach. The aircraft landed safely at Winnipeg.
Technical Investigation
The horizontal stabilizer trim actuator (Barber-Colman P/N 27-1900-002, S/N 115) was removed for analysis. Testing revealed that the "no-back" mechanism failed to hold under minor loads. An outboard ball bearing on the copilot's side had disintegrated, destroying the trunnion gear teeth and allowing the actuator output tubes to move unrestrained by air loads. The deformation of the no-back rollers indicated they had been subjected to abnormal repetitive loads prior to the failure.
Contributing Factors
Inspection showed signs of mis-rigging of the full-retract position, which placed stress on the gear system, though this was not deemed the direct cause of the component failure. The actuator had been overhauled in May 1996 and had accumulated 1,439 air hours at the time of the incident. Post-incident, Fairchild Aircraft updated maintenance manuals to require specific checks for mechanical and electrical stops, and the FAA issued Airworthiness Directive 97-23-01 for repetitive inspections of similar actuators.