Incident Overview
The instructor pilot and dual student reported that during a landing, the nose gear and subsequently the main gear collapsed after the airplane touched down on its landing gear. The green indicator light, which signals that the gear is down and locked, was illuminated at the time of touchdown.
Investigation Findings
Examination of the aircraft revealed evidence that the landing gear was up and locked when the airplane contacted the runway. During testing, one of the landing gear circuit breakers, specifically the one for the dynamic brake relay, would 'pop' (trip). The dynamic brake relay is designed to prevent the landing gear motor from overrunning and jamming in the up or down position.
Despite this, the gear extension and retraction system, including the indicator lights and warning horn, operated normally. The up/down lock position appeared to be correct. No part failure or malfunction was identified that would have resulted in the accident.
Systems Description
The landing gear system includes a dynamic brake relay that controls the motor to prevent overtravel. The circuit breaker that popped is associated with this relay, but its tripping did not correlate with any observed component failure.
Conclusion
The investigation concluded that the landing gear collapse occurred after touchdown, but the precise cause could not be determined, as no mechanical or electrical fault was found.