Incident Overview
During a routine landing, the aircraft's nose gear collapsed as the pilots were completing the landing. The pilots reported that three green indicator lights illuminated during the final landing checklist, indicating the landing gear was down and locked.
Investigation Findings
Postaccident troubleshooting revealed that an instrument panel mounting screw was excessively long. This screw obstructed the movement of the landing gear selector handle, preventing it from reaching the full down position. The handle would prematurely return to neutral, which removed hydraulic pressure from the landing gear system. As a result, the nose gear was not hydraulically moved over center and remained unlocked, despite the indicator lights showing a down-and-locked configuration.
Aircraft System Details
According to the aircraft service manual, the nose gear linkage incorporates a downlock spring. Additionally, both the gear linkage overcenter travel and the gear down limit switch position are adjustable. However, it was not determined whether these items had been checked or adjusted prior to the accident.
Corrective Action
After the improperly long screw was replaced with the correct one, the landing gear system operated properly during retraction tests.