As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AIRCRAFT WAS ON APPROACH AND SELECTED LANDING GEAR DOWN. LANDING GEAR FAILED TO EXTEND. THE FLIGHT CREW THEN SELECTED THE EMERGENCY LANDING GEAR EXTENSION SYSTEM. THE LANDING GEAR LOCKED DOWN AND THE AIRCRAFT LANDED SAFELY. UPON INSPECTION OF THE LANDING GEAR SYSTEM MAINTENANCE FOUND THE RETAINING RING INSTALLED IN THE SHAFT COUPLER MISSING. THIS CAUSED THE COUPLER TO SLIDE TO THE MOTOR SIDE OF THE SPLINED SHAFT, WHICH CAUSED THE MOTOR TO DISENGAGE FROM THE PUMP.