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Summary

Summary

After arrival in the circuit, when the landing gear was selected down, the pilot reported there was an unusual noise followed by a pronounced 'clunk', and the extension cycle stopped. The red gear unsafe light was illuminated and the gear motor circuit breaker had tripped. The checklist was reviewed and the pilot attempted to extend the gear using the emergency system. The emergency extension handle unlatched normally however, the handle was very difficult to move and jammed after about 30 degrees of its travel. The pilot eventually landed the aircraft on runway 29C with the landing gear partially extended. A subsequent investigation revealed that the interconnect shaft between the forward main gear door motor and the rear main gear door lock mechanism had disconnected. This prevented the rear door locks from unlocking. The gear extension electric motor attempted to drive the gear down with the doors still locked closed, the motor stalled and the circuit breaker tripped. The heavy load on the rear doors prevented the pilot from releasing the door latches by the emergency extension system. The interconnect shaft is normally retained by a bolt and split-pinned nut. These items were missing and were not recovered after the accident. The aircraft had undergone maintenance, which included an inspection of the landing gear, some 16 hours prior to the accident.
 
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