Date: 201207
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Weather elements / visibility: 10
Light: Daylight
Aircraft: MU-2
Operator: Personal
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: Nose Gear
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Pilot Flying
Reporter qualification: Flight Crew Multiengine
Human factors: Situational Awareness; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance; Person Flight Crew
When detected: Other Post incident
Result: Aircraft Aircraft Damaged; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Human Factors

Narrative: ZZZZ to ZZZ VFR; landed; then while taxing to end of Runway to go to Customs; front of plane lowered about 8' inches; I assumed flat tire. Instead of stopping on runway; I exited onto gravel North of runway and stopped plane; called Tower and stated clear of runway and that we would need a tow. Upon exiting plane with my family; I inspected the plane and found no damage to airframe; propellers; or [Landing] Gear doors. It appeared the Nose Gear was aft of its normal position. Fire Department; Sheriff's Department and Customs arrived and Fixed Base Operator (FBO) with there Toter [Tow Vehicle]. They were trying to load the plane on Toter when the Airport Manager (APM) loaded us in his car and drove us to FBO. This being hurricane season; I cannot leave this plane sitting in ZZZ. I called my Mechanic; he said to tear it [Landing Gear] apart and get some Part Numbers (P/Ns) and he will be down and repair. I went down the next day to ZZZ and found they damaged plane while towing it to parking area. When front Nose Gear removed; found right-hand Upper Trunnion bolt to be broken off. Upon examination by Mechanic; part had been drilled wrong and cracked and split over time. I think removal of all Trunnion parts during Annual [Inspection] would prevent this. You would not find this by just swinging the [Nose] Gear. Airplane was examined and repaired by Mechanic and Returned to Service (RTS) approximately seven days later.

Callback: Reporter stated this incident was not caused by a design failure of the Nose Gear Trunnion pin. While reviewing the previous Maintenance records of the MU2 aircraft; he and his Technician noticed the Nose Gear had been struck by a vehicle several years earlier and replaced. But the Repair Station used by the aircraft Manufacturer had installed a used Trunnion pin at the right-hand position when the Nose Gear was replaced. That was the same Trunnion pin that broke. Trunnion pins are held in placed with two bolts. Reporter stated the Left Hand (L/H) Nose Gear Trunnion pins are a solid pin due to the Nose Gear door Actuator being mounted in the area of the pin. But the Right Hand (R/H) Trunnion pins are actually a hollow type pin that comes un-drilled when new. The 'used' hollow Trunnion pin had previous drill holes that did not line-up on one side of the pin for the attach bolts to go through. So the Mechanic at that Repair Station drilled a new hole on one side of the Trunnion pin so the attach bolt would go through. Because the two drilled holes on one side were so close to each other; that over time; the metal in between cracked and migrated towards each other; causing a figure-eight shaped hole. The top portion of the hollow pin broke away; shifting the Nose Gear R/H Trunnion forward; repositioning the Nose Gear R/H Locking Brace out of the 'Lock' position and collapsing the Nose Gear eight inches. If the L/H locking Brace had also shifted; the entire Nose Gear Assembly would most likely have collapsed into the wheel well causing additional damage to the engines; propellers and Nose Gear doors.Reporter stated he feels his incident was caused by a one time; isolated situation involving improper maintenance and not a systemic issue with the Trunnion pins or the aircraft Manufacturer's assembly process.



Synopsis: Pilot reports his Mitsubishi MU2 aircraft Nose Landing Gear collapsed eight inches after landing. A reused right-hand Nose Gear Trunnion pin had failed due to improper maintenance.