What happened
On 30 May 2015, a PA-28RT-201T training flight operating out of Grenchen regional airport encountered significant technical difficulties during its fifth approach. The crew noticed that the left main landing gear failed to extend fully, despite the nose and right gear showing green indicators. Following an initial go-around and subsequent troubleshooting maneuvers, the crew performed several low-passes to visually inspect the gear status with the assistance of air traffic control.
After attempting emergency extension procedures and high-g maneuvers to force the gear into position, the crew decided to land on the hard-surface runway 25. During the landing flare, the instructor shut down the engine. As the aircraft touched down, the left main landing gear collapsed. The aircraft veered left, exiting the runway approximately 260 meters beyond the touchdown point, before coming to a stop on the adjacent grass. There were no injuries to the three occupants on board.
The investigation
SUST examined the mechanical state of the landing gear and the hydraulic systems of HB-PLC. The investigation focused on why both the standard extension method and the emergency "free fall" procedure failed to lock the left gear. Investigators analyzed the electrical wiring and the physical condition of the landing gear components, including the bolts and bores.
Findings
Technical analysis revealed that the left main landing gear leg was subject to increased mechanical resistance caused by fretting on the bolt and bore, likely due to inadequate lubrication. Additionally, a cable break near the down-lock switch caused the hydraulic pump to shut down prematurely. This prevented the hydraulic system from maintaining pressure long enough to lock the left gear in the extended position. Because the pump stopped once the other two gears were confirmed locked, the left leg remained stuck in an intermediate position, making it susceptible to collapse upon ground contact.