What happened
On August 1, 2021, a privately owned Piper PA-46-350P, registration JA4077, was performing a familiarization flight at Sendai Airport. After completing four touch-and-go maneuvers, the aircraft approached Runway 12. The pilot maintained an approach speed of 80 to 85 knots, managing a crosswind from the right front.
During the landing roll, the aircraft began to veer significantly to the left. As the pilot applied right rudder to correct the direction, the aircraft suddenly tilted forward. The nose landing gear collapsed toward the retracted position, causing the lower forward fuselage and the tips of the three propeller blades to strike the runway surface. The aircraft came to a stop in the middle of the runway. There were no injuries to the two occupants on board.
The investigation
Investigators examined the aircraft's engine mount and landing gear assembly to determine why the gear failed while the actuator was in the down-locked position. The investigation, which included analysis by the Japan Aerospace Exploration Agency (JAXA), focused on the fractured right actuator attachment foot.
Technical analysis revealed that the fracture surface showed evidence of partial corrosion and the presence of blisters. Chemical testing of the welded portion of the attachment foot showed a deficiency in chromium, which reduced the metal's corrosion resistance. Furthermore, the aircraft was typically parked outdoors at a coastal airport, exposing it to a humid, salt-laden environment.
Findings
- The collapse of the nose landing gear was caused by the fracture of the right actuator attachment foot, which forced the landing gear loads onto the left foot, eventually deforming the engine mount.
- The fracture likely originated from cracks on the inner surface of the attachment foot, which developed over time due to landing impacts and subsequent flight cycles.
- Corrosion and the formation of blisters on the inner surface of the welded part likely weakened the component and contributed to the crack progression.
- The chromium-deficient welded area made the component more susceptible to environmental degradation.
- While the manufacturer had issued a Service Bulletin (SB 1103F) recommending fluorescent penetrant inspections every 100 hours, the most recent 100-hour inspection in November 2020 had only included a visual check, which failed to detect the internal cracking.