What happened
At approximately 20:46 Pacific standard time, an Airbus A330, registration C-GGWA, departed from Vancouver International Airport. Shortly after lift-off, the flight crew received reports from passengers and cabin crew regarding a loud impact sound. A passenger subsequently observed an object falling from the left engine or wing area.
To assess the damage, a deadheading captain inspected the engine area using wing lights. The inspection revealed that the outboard fan cowl of the left engine was missing. The departing cowl had struck the left wing's leading edge, damaged the fuselage-to-wing fairing and a hydraulic access panel, and made contact with the vertical stabilizer. The separation also caused substantial damage to the left engine pylon. Despite the structural damage, there were no cockpit indications of abnormal handling, and the crew successfully returned to Vancouver.
The investigation
The investigation focused on the maintenance activities performed prior to the flight. On the evening of the occurrence, the aircraft underwent several maintenance tasks, including the replacement of a thrust reverser directional pilot valve on the left engine. This work was performed by an apprentice mechanic under the supervision of qualified engineers.
Investigators examined the damaged components and compared them to undamaged aircraft in the fleet. They identified several mechanical and procedural issues. Specifically, they found that the latch fitting sub-assemblies had been assembled with bolt threads and nuts facing inward, which caused interference with the safety pins, leading to bent or broken pins. Furthermore, the investigation found that approximately 80% of the examined cowls were below the manufacturer's required minimum latch tension.
Findings
- At least one cowl latch was not properly secured or failed to lock, which allowed the fan cowl to open during the takeoff roll.
- The flight crew's pre-flight inspection was ineffective because it was conducted before the maintenance work was fully completed.
- The design of the latching mechanism makes it difficult to visually confirm if latches are secured, as the handles are located on the underside of the engine and are often camouflaged by similar paint colors.
- The use of tools to operate latches, rather than manual force, may have damaged the internal spring mechanisms or the safety pins.
- Current maintenance requirements for verifying latch tension are inadequate to ensure the system remains properly adjusted.