What was found
RTFL WITH A LANDING GEAR DOOR WARNING MESSAGE. PROBLEM REOCCURED ON SUBSEQUENT FLIGHT. [SUP 05-08-07] AFTER RTFL OF FLIGHT 543, FAULT WAS ORIGINALLY TRACED TO A LOOSE PROXIMITY SWITCH. SWITCH WAS SECURED AND OPS CHECKED OK. ON NEXT FLIGHT, SAME WARNING MESSAGE OCCURRED FOLLOWED BY ANOTHER RTFL EVENT. SUBSEQUENT FAULT TRACING FOUND THE DOOR CLOSE SAFETY VALVE TO BE DEFECTIVE. SAFETY VALVE WAS REPLACED AND GEAR WAS CYCLED 5 TIMES DURING A VERIFICATION FLIGHT TO ENSURE PROPER OPERATION.