What was found
IAH- DURING APPROACH FLIGHT 3989, THE CREW NOTED THE FOLLOWING, THE LANDING GEAR WOULD NOT COME DOWN. LEFT GEAR SYSTEM -A- LIGHT (GREEN) ON AND ALL OTHER RED LIGHTS ILLUMINATED (SYSTEM-B AND RIGHT AND NOSE SYSTEM-A). GEAR WAS CYCLED, BUT DID NOT COME DOWN UNTIL AFTER GO-AROUND IN A 30 DEGREE BANK. MAINTENANCE REMOVED AND REPLACED THE LANDING GEAR CONTROL RELAY BOX, PERFORMED A OPERATIONAL CHECK OF THE LANDING GEAR SYSTEM, NO DEFECTS NOTED AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.