What happened
During a scheduled night freight flight departing from Hamilton, Ontario, a Convair 580 experienced a sudden and severe nose-up pitch as it approached liftoff speed. The aircraft became airborne with minimal input from the captain, and the nose-up attitude intensified as the plane accelerated. Despite the crew applying full nose-down trim and exerting significant physical force on the control column—with both pilots using their feet to push the column forward—the pitch remained difficult to manage.
To maintain control, the crew experimented with various power and flap configurations, eventually discovering that entering a moderate turn allowed them to induce a descent. After notifying Hamilton air traffic control of their control difficulties, the crew returned to the airport. They requested emergency response services, though the aircraft landed safely on runway 24 before the vehicles arrived. There were no injuries and no damage to the aircraft.
The investigation
Investigators examined the aircraft's maintenance history and found that recent work had been performed on the elevator and elevator trim. The investigation revealed that the elevator trim tab was functioning in reverse, moving in the opposite direction of the cockpit trim indicator and control wheel.
At the maintenance facility, the stabilizer and elevator had been removed for inspections. During the reinstallation, the elevator trim control cables were crossed. The investigation found that the cables had not been marked during disassembly, and the maintenance manual's diagrams were ambiguous regarding the cable orientation. Furthermore, the crew performing the reinstallation consisted largely of apprentices under the supervision of a crew chief, and the licensed engineer tasked with the independent inspection failed to verify the sense of operation of the trim system.
Findings
- The aircraft was dispatched with the elevator trim operating in reverse due to the improper connection of control cables.
- The crew chief incorrectly identified and connected the elevator trim control cables in a crossed configuration.
- The licensed engineer performing the final inspection did not adequately verify the direction of the trim tab movement.
- The maintenance manual provided ambiguous illustrations that could lead to the cables being installed incorrectly.
- The crew misdiagnosed the flight control issue as a center of gravity problem caused by shifting cargo.
- The maintenance task was performed by a crew of apprentices and a crew chief without the presence of the original installation team or sufficient lead engineers.