As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SFO - CREW REPORTED MAIN GEAR FAILED TO EXTEND ON INITIAL EXTENSION. ALL OPERATIONS NORMAL ON SECOND EXTENSION ATTEMPT. MAINTENANCE INSPECTED LANDING GEAR MICROSWITCHES AND WIRE CONNECTIONS ON GEAR CONTROL VALVE. NO DEFECTS NOTED. COULD NOT DUPLICATE DISCREPANCY. AIRCRAFT RETURNED TO SERVICE. (M)