What was found
(CAN) THERE HAVE BEEN 4 OCCURRENCES, THE 4TH WAS A TEST FLIGHT, WHERE THE ACFT TOOK OFF AND THE LANDING GEAR WOULD NOT RETRACT. THE WEIGHT ON WHEELS SWITCHES WERE CLEANED, THE CABIN SAFETY VALVES WOULD NOT CLOSE DUE TO A FAULT IN THE WEIGHT ON WHEELS SYSTEM, AND GEAR SWINGS WERE CARRIED OUT WITH NO DEFECTS NOTED. THE ACFT FLEW 6 LEGS OVER 3 DAYS WITHOUT FURTHER INCIDENT. THE NLG WOW SWITCHES WERE REPLACED AND THE LOWER NLG STRUT BEARING WAS CLEANED, GEAR SWINGS WERE CARRIED OUT WITH NO DEFECTS NOTED. THE LT OTBD MLG WOW SWITCH WAS REPLACED AND GEAR SWINGS WERE CARRIED OUT WITH NO DEFECTS NOTED, THE ACFT WAS RELEASED SUBJECT TO A SATISFACTORY TEST FLIGHT. THE TEST FLIGHT WAS UNSATISFACTORY, MAINTENANCE IS REPLACING THE NLG ASSY WITH A REPAIRED UNIT.