Crash of a Dassault Falcon 10 in Detroit

The pilot reported getting an unsafe indication on the right main landing gear when the landing gear was lowered. The crew recycled the landing gear and got the same unsafe indication. The crew retracted the gear and diverted to Detroit. On arrival, the crew performed the 'landing gear abnormal extension checklist,' but the unsafe indication remained. The air traffic control tower reported that the gear appeared normal. During the landing, the right main landing gear retracted. The airplane slid sideways, striking a runway marker as it departed the runway, and came to rest in a field. Examination revealed that the right landing gear downlock mechanism could be overcome with physical force. Examination of the right landing gear actuator revealed that one of the six shims which separate the spacers and help guide the safety lock switch was out of position and lying on top of the lock assembly.