What happened
On 5 April 1999, a Piper PA-31, registration G-OPRA, was conducting a passenger flight when the pilot encountered issues with the landing gear during the approach to Blackpool Airport. Approximately 10 miles from the airfield, the pilot extended the gear, noting that while the nose and right main gear indicated they were locked, a red 'gear unsafe' light was illuminated. An attempt to retract the gear to reset the system failed, as the gear lever became stuck in the neutral position.
During a flypast of the control tower, it was observed that the inboard door of the left main landing gear was extended, though the gear leg itself remained retracted. The pilot performed several maneuvers, including emergency gear lowering procedures and additional circuits, to attempt to unlock the left leg. Due to declining fuel levels and following advice from engineers, the pilot opted to land. The landing was performed with the left engine shut down and the propeller feathered. The aircraft touched down on the nose and right main wheels; the pilot attempted to keep the left wing elevated, but the wing eventually made contact with the runway before the aircraft exited onto the grass.
The investigation
Technical examination of the aircraft focused on the left main landing gear assembly. Investigators discovered that the oleo strut had deflated. This loss of pressure was caused by a seal that had rolled rather than sliding down the felsalised portion of the ram. This mechanical failure resulted in a shortened oleo length, which prevented the uplock mechanism from releasing the gear leg.
Findings
- The primary cause of the landing gear failure was a seal failure within the left main landing gear oleo.
- The seal had rolled instead of sliding, leading to the deflation of the strut.
- The resulting reduction in the length of the oleo prevented the release of the uplock.
- The seal in question had been replaced approximately one month prior to the incident.