What happened
On February 17, 2003, a PIPER PA-28R-180 was conducting a dual instruction flight between Valencia and Castellón airports. After completing takeoff and landing maneuvers at Castellón, the crew returned to Valencia. During the approach to runway 12, the crew noticed that the landing gear lights failed to indicate the gear was down and locked. They subsequently retracted and re-extended the gear, at which point the three green lights illuminated, and they landed normally.
While taxiing toward taxiway H-2 after landing, the pilot received a landing gear warning indicating the right leg was unsafe. Simultaneously, the aircraft began to sink on the right side. The pilot immediately stopped the aircraft, and both the instructor and student pilot evacuated the plane safely. No injuries were reported, and there was no fire or fuel spill.
The investigation
Technical investigators examined the right main landing gear, specifically focusing on the outer cylinder, the front pivot pin, and the connecting bolt. The investigation included macro- and micro-fractographic analysis, as well as hardness testing conducted by the National Institute for Aerospace Technology (INTA).
Physical inspection revealed that the front pivot pin had been severed at the junction where it meets the gear leg. Additionally, the bolt used to secure this pin to its housing had also broken. The investigation noted that the bolt's location inside a drilled hole within the pin made it impossible to verify its condition through visual inspection without disassembly. Maintenance records showed the aircraft had undergone regular inspections, but the specific components in question had not been removed for inspection since the aircraft was acquired in 1996.
Findings
- The fracture of the front pivot pin was identified as a progressive failure caused by fatigue.
- The connecting bolt also failed due to a high-cycle fatigue mechanism.
- Analysis of the bolt's fracture pattern ruled out a sudden static overload, which would have occurred if the pin had broken first.
- The investigation concluded that the most probable cause was that both the pin and the bolt were simultaneously affected by fatigue, triggered by inadequate tightening torque applied to the bolt.