What happened
Prior to the accident flight, maintenance personnel performed work on all four engine thrust reversers of the aircraft. During this process, a mechanic went off-shift before the number 2 cowl was closed, requesting that another mechanic complete the task. The second mechanic lowered both the number 1 and number 2 cowl doors but was unable to properly secure or lock them. This individual noted in the shift turnover log that all four engine cowls required securing.
When the following shift of mechanics arrived, they observed that the number 1 and 2 cowls were closed. However, these mechanics did not review the shift turnover log and failed to verify that the cowls were latched. During the preflight inspection, the flight engineer also failed to identify the unlatched cowls, despite company flight operations manual procedures requiring a check to ensure they were secured.
The flight crew initiated takeoff with the number 1 and 2 engine cowls unsecured. During and shortly after the takeoff phase, both cowls departed from the aircraft. The separation caused substantial damage to the left wing and the left horizontal stabilizer. The flight crew subsequently returned to the departure airport and landed without further incident; there were no injuries.
Findings
- Maintenance personnel failed to properly secure and lock the number 1 and 2 cowl doors.
- The incoming maintenance shift did not consult the shift turnover log or verify the latch status of the cowls.
- The flight engineer's preflight inspection failed to detect the unsecured hardware despite established inspection protocols.