What happened
On 07 April 2000, a Cessna 172, registration C-FAXL, was undergoing an annual inspection at an airport in Amos, Quebec. Following the inspection, the pilot departed the airport at approximately 1645 EDT. Roughly 13 nautical miles from the airport and at an altitude of 2700 feet, the pilot experienced a loss of aileron control. The pilot managed to land the aircraft safely using the elevator, rudder, and trim tab, though no emergency was declared at that time.
Upon returning to the hangar, a maintenance manager discovered that the right-hand aileron yoke assembly had detached, with components found on the aircraft floor. To avoid working in the dark, the manager performed the repairs personally, reinstalled the universal joint, and returned the aircraft to service without a technical entry or an independent inspection.
Four days later, on 11 April 2000, the same aircraft was flying from Mont-Laurier toward Trois-Rivières. Approximately 70 nautical miles from Maniwaki, the right-hand aileron yoke assembly failed for a second time. This failure caused the left aileron to rise, destabilizing the aircraft. The pilot utilized the elevator and rudder to maintain control and landed at Maniwaki, where emergency services were waiting. There were no injuries during either incident.
The investigation
The investigation focused on the maintenance procedures performed at Avionnerie Amos. It was established that the maintenance manager had suggested rotating the existing universal joints rather than replacing the defective one to save costs, which increased the complexity of the task.
Investigators found that the technician worked in a restricted space without removing the radio card box, which would have allowed for better visibility. The gap between the shaft and the bearing was measured at nearly 0.500 inch, significantly exceeding the required 0.005 inch specification. Furthermore, the maintenance manager failed to conduct the mandatory independent inspection required by the Canadian Aviation Regulations for flight control systems, and the work was not recorded in the aircraft's technical logs.
Findings
- The Cessna 172 was returned to service on two separate occasions with an incorrectly installed aileron control system, leading to the loss of lateral control.
- A required independent inspection was not performed in either instance, which could have identified the assembly error.
- The failure to remove the radio card box during maintenance prevented adequate access and visual verification of the components.
- The decision to rotate the universal joints instead of replacing them increased the difficulty of the installation and the likelihood of error.