What happened
On August 30, 2008, an Air Finland Boeing 757, registration OH-AFJ, was operating a ferry flight from Copenhagen to Helsinki when a hydraulic bay access door detached from the aircraft. Following takeoff, the crew observed "GEAR DISAGREED" and "GEAR DOORS" messages on the Engine Indicating and Crew Alerting System (EICAS). The aircraft had previously returned to Copenhagen after an earlier departure due to similar landing gear warnings. During the maintenance stop in Copenhagen, technicians addressed the gear door issue by trimming a rubber seal, but the gear disagreement issue remained unresolved.
Following the second departure, the crew operated the aircraft with the landing gear in the up position, though the left main gear remained slightly down and the left main gear door was fully open. Approximately 10 to 20 minutes into the flight, turbulent airflow caused the hydraulic bay access door to open and eventually tear away from its hinges. In accordance with the Quick Reference Handbook (QRH), the crew continued the flight at a reduced speed of 270 knots and a lower altitude of FL280. Upon landing in Helsinki, the crew discovered the missing access door and minor structural damage to the lower fuselage.
The investigation
The investigation focused on the status of the hydraulic bay access door and the underlying landing gear malfunctions. Investigators examined the maintenance records from Copenhagen and the physical damage to the aircraft's secondary structure. The inspection revealed that the door's impact against the fuselage had created a 1.5 cm x 3.0 cm hole in the composite structure and damaged nearby lighting.
Further technical examination in Helsinki identified that the landing gear issue was caused by internal wear within the left main gear actuator, which led to an internal hydraulic leak and prevented the gear from locking properly in the up position. While maintenance personnel stated they did not open the hydraulic bay access door, investigators determined it was likely opened during the extended ground time in Copenhagen and not properly secured.
Findings
- The primary cause of the incident was turbulent airflow acting upon an improperly secured hydraulic bay access door.
- The maintenance actions in Copenhagen focused solely on the "GEAR DOORS" warning, leaving the "GEAR DISAGREED" issue unaddressed.
- It is highly probable that the access door was opened during the aircraft's stay on the ground and was not correctly closed and locked.
- The pilot's pre-flight inspection and the personnel who released the aircraft failed to detect the improperly secured door.
- The landing gear malfunction was traced to internal wear and a resulting hydraulic leak in the left main gear actuator.