What happened
On January 14, 2014, a Saab 340A operated by a commercial airline was performing a scheduled flight from Gdańsk Lech Wałęsa Airport (EPGD) to Warsaw Chopin Airport (EPWA). Prior to departure, both a ground mechanic and the flight crew performed inspections of the aircraft; both checks confirmed that all cowlings were properly secured and no loose covers were present.
During the takeoff roll and initial climb, the crew experienced significant vibrations. While engine parameters remained within normal operating limits for the assigned takeoff power, the crew identified that the left engine cowling had opened. The frequency of the vibrations corresponded to the flapping motion of the unsecured cover. The crew immediately initiated a go-around and returned to EPGD. After leveling off at 3,000 feet and stabilizing at 160 knots, the cowling closed on its own, and the vibrations ceased. The aircraft landed safely without further incident.
The investigation
Post-flight inspections of the engine compartment and cowling revealed edge damage and dents on the surface of the cover, though no structural failure of the hinges or locks was found, and the engine compartment itself remained undamaged.
Technical examination determined that the security mechanism for the forward lock had become loose, allowing it to be disengaged by vibration. The investigation established that the direction of the airflow during flight aligned with the opening direction of both the lock and the cowling itself. It was determined that the simultaneous effects of engine-induced vibrations and aerodynamic pressure caused the loosened security mechanism to release, subsequently allowing the forward lock to open. Although the rear lock remained engaged, the aerodynamic pressure forced the cowling to deform sufficiently to allow it to swing open.
Findings
- The primary cause of the incident was the opening of the engine cowling in flight due to the disengagement of the security mechanism.
- The disengagement was caused by the combined impact of engine vibrations, aerodynamic airflow, and mechanical looseness resulting from long-term operational wear.
- The forward lock security mechanism had become loose enough to allow accidental unlocking under vibration.