What happened
On 25 January 2025, a Socata TB-20 Trinidad, registration G-BSCN, was returning to Blackbusle Airport after a night navigation training exercise. As the pilot prepared for landing, the selection of the landing gear down position resulted in an unsafe indication; while the nose and right main gear appeared locked, the left main gear light remained unlit.
In an attempt to resolve the issue, the pilot cycled the landing gear and utilized the emergency extension system. However, these actions failed to rectify the status, and eventually, all three gear components indicated as not locked. To verify the gear's position, the pilot performed a low flypast, during which ground personnel observed that the gear appeared to be down. Relying on this visual assessment, the pilot proceeded with the landing. Shortly after the aircraft touched the runway, the right main landing gear collapsed. The aircraft slewed to the right, causing the right wingtip, aileron, and flap to contact the runway. There were no injuries to the pilot or the passenger.
The investigation
Investigators examined the aircraft's retractable tricycle landing gear system, which relies on hydraulic actuators powered by an electrically driven hydraulic power pack. Testing conducted while the aircraft was on jacks revealed that the electrically driven hydraulic power pack failed by running sporadically and starting or stopping at random intervals.
Further testing of the emergency lowering system showed that while it functioned correctly when the gear was near the fully retracted position, it was ineffective if the power pack motor ceased operation before the downlock latches engaged. In such instances, the gear could appear visually extended without being mechanically locked, and gravity alone provided insufficient momentum to engage the latches.