Incident Overview
Upon arrival in the traffic pattern of the destination airport, the pilot lowered the landing gear selector handle, but the landing gear did not extend. The flight departed the pattern, and attempts to lower the gear via the emergency method were unsuccessful. Consequently, the flight diverted to a larger airport where a gear-up landing was performed.
Post-Inspection Findings
After the event, the landing gear retract motor and gearbox assembly were removed from the aircraft and disassembled. Disassembly revealed that the worm sector gear had repeatedly contacted the sector gear stop. Additionally, two half rings that secure the bearing to the worm actuating shaft had sheared. This allowed the worm gear actuator to travel toward the motor. As a result, the hand crank engaging shaft would not contact the worm gear actuator.
According to a mechanic, this condition was due to a worn landing gear motor. The worn motor would still drive the gear but would render the dynamic braking action inoperative. The up-limit switch was tested and found to operate normally.