Incident Overview
On a routine flight from Montréal to Québec, Air Canada Jazz Flight JAZZ8710, a de Havilland DHC-8-300 (registration C-GABP), encountered an aileron trim tab malfunction shortly after departure. The aircraft carried three crew members and three passengers. At approximately 3000 feet above sea level, the aircraft began banking left, requiring force on the control wheel to maintain level wings. The flight crew executed the runaway aileron trim tab checklist, which resolved the roll tendency. However, the trim tab indicator showed a full deflection to the right, which the crew deemed abnormal. Emergency services were alerted, and the flight continued to Québec City.
Pre-Flight Procedures
The aircraft was authorized to fly under Minimum Equipment List (MEL) 27-1 due to a defective aileron trim tab indicator, which required a visual check of the trim tab before each departure and a placard near the indicator. The investigation found that no visual check was performed, and no placard was present. The previous flight crew had complied with the MEL procedure before their flight from Québec, during which no trim tab issues arose.
The occurrence flight was the crew's third of the day but their first on C-GABP. The first officer noted the MEL reference in the flight plan and informed the captain. The captain intended to review the aircraft logbook after boarding but did not check the trim tab during the external inspection because he had not yet read the logbook, which would have referenced the MEL procedure. Maintenance personnel informed the crew of a reported severe airframe vibration from the previous flight and installed a propeller balancer. The logbook contained two Part 2 sections; the captain saw only the newer Part 2, which noted the vibration, but missed the defective trim tab indicator entry in the older Part 2 underneath.
In-Flight Events
After a normal take-off at 0958, the first officer (pilot flying) noticed the aircraft's tendency to bank left at level flight, with the trim tab indicator fully right. The captain took control and confirmed the roll. After completing the runaway trim tab checklist, the indicator remained fully deflected right, but the roll ceased. The crew decided to proceed to destination, suspecting that a poorly fastened panel on the wing had separated, causing resistance requiring full trim tab deflection. The captain contacted the maintenance coordinator, reporting control problems and suggesting a lost panel. The maintenance coordinator notified the flight dispatcher, who initiated a category C emergency message and alerted ATC. Emergency equipment was placed on standby.
During the approach to Runway 24 at Québec, the crew received a message from the airline, via the controller, not to continue the approach. The aircraft was less than two miles from the threshold at about 665 feet agl. The crew initially continued but then executed a missed approach when a subsequent instruction was received at approximately 65 feet agl, descending to below 50 feet during the maneuver. The captain called the airline for explanation. The director of flight operations, having heard about a lost panel, recommended a no-flaps landing for greater aileron effectiveness. The aircraft returned and landed without flaps at 1052 eastern standard time.
Post-Flight Findings
The investigation revealed that the trim tab indicator had been intermittently defective since 26 March 2004, with prior repairs. After the flight, the trim tab was found centered but incorrectly adjusted: downward deflection was only 15 degrees instead of the specified 20 degrees, allowing 25 degrees upward and 15 degrees downward. This misadjustment could have caused the trim tab indicator to show neutral while the tab was actually deflected upward. Two factors indicated that the roll tendency likely resulted from the tab being up: the runaway checklist corrected it, and the tab was neutral upon arrival. It could not be determined why the tab was deflected upward, but possibilities include accidental actuation during pre-flight or propeller balancer installation, or the crew using the malfunctioning indicator as a reference. The defective indicator had been noted in the flight plan but overlooked by the captain.