As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 3720 HAD TO RETURN TO FIELD DUE TO HAVING THE RIGHT AND LEFT MAIN GEAR UNSAFE LIGHTS ILLUMINATE AFTER THE GEAR WAS RETRACTED. THE CREW USED THE ALTERNATE EXTENSION AND LANDED WITHOUT INCIDENT. MAINTENANCE WAS ABLE TO DUPLICATE THE CONDITION. IT WAS FOUND THAT THE LANDING GEAR UPLOCK PROXIMITY SENSOR NEEDED TO BE ADJUSTED. GAP WAS ADJUSTED AND THE GEAR WAS OPERATED SEVERAL TIMES. ALL SYSTEMS CHECK GOOD. AIRCRAFT RETURNED TO SERVICE.