What happened
An Air Canada Jazz DHC-8-300, registration C-GABP, was operating a scheduled flight from Montréal to Québec with three crew members and three passengers. Shortly after takeoff, while climbing to approximately 3,000 feet, the aircraft began to bank to the left. The flight crew observed that the aileron trim tab indicator was deflected fully to the right, yet the aircraft required manual steering input to maintain level wings. After performing the runaway aileron trim tab checklist, the rolling tendency ceased, but the crew noted the abnormal indicator position and requested emergency services.
During the approach to Runway 24 at Québec, the crew received conflicting instructions from the airline's dispatch center. An initial instruction advised them not to continue the approach, prompting the crew to consider a different landing configuration. However, a subsequent, second instruction to execute a missed approach was delivered by the tower only when the aircraft was at an altitude of approximately 65 feet above ground level. The crew executed the maneuver, descending to less than 50 feet before completing a successful no-flaps landing.
The investigation
The TSB examined the aircraft's maintenance history, the logbook entries, and the communication chain between the flight dispatch center and the air traffic controller. The investigation focused on why the crew was unaware of a known defective trim tab indicator and why the instruction to go around was delayed until a critical low-altitude phase of flight.
Investigators found that the aircraft was authorized to fly under the Minimum Equipment List (MEL) due to the defective indicator. This required a visual external check of the trim tab and the placement of a warning placard near the cockpit indicator. However, neither the visual check nor the placard was present. The investigation also scrutinized the logbook, which had been reorganized with a new section, causing the entry regarding the defective indicator to be obscured behind more recent entries regarding aircraft vibration.
Findings
- The aileron trim tab was improperly aligned, which contributed to the aircraft's tendency to roll during the departure from Montréal.
- The crew was unaware of the defective trim tab indicator because of the absence of a required placard and the disorganized arrangement of the aircraft logbook.
- A lack of clear task distribution between the assistant chief dispatcher and the flight dispatcher caused confusion during telephone communications with the tower, which delayed the transmission of the missed approach instruction to the pilots.
- The decision to execute a missed approach at such a low altitude created a high-risk situation during a critical phase of flight.