What happened
On July 4, 2019, a Petrel 912i, registration LV-FVC, was conducting a general aviation training flight from General Rodríguez to Pergamino, Buenos Aires. After a routine landing on runway 22 under visual flight conditions, the aircraft was taxiing toward the apron when the pilot experienced intense vibrations originating from the nose landing gear. Shortly thereafter, the nose gear suffered a structural collapse, causing the propeller to strike the asphalt runway surface. The impact destroyed the propeller and caused the engine to stop abruptly. The pilot sustained no injuries during the incident.
The investigation
The JST investigation focused on determining the cause of the gear failure and assessing whether the structural integrity of the nose gear on this aircraft model was compromised. Investigators examined the nose gear fork, which is constructed from SAE 4130 steel tubing. Metallurgical analysis revealed that the welding process used during construction had created a significant stress concentrator. Specifically, the study identified the presence of brittle martensitic structures in the area immediately adjacent to the weld bead. This metallurgical alteration created a hidden defect that was not detectable through standard visual inspections or common non-destructive testing methods used for surface cracks.
Findings
- The structural collapse of the nose gear was caused by the propagation of cracks near the weld bead of the fork.
- These cracks originated due to an alteration of the material's crystalline structure caused by the welding process.
- The aircraft was not being maintained in accordance with current regulatory requirements, with discrepancies noted between recorded maintenance tasks and actual aircraft activity.
- There was no evidence that the component had been subjected to loads exceeding its design limits during normal operations.
- Standard preventive maintenance inspections are unable to effectively detect this specific type of internal, hidden structural damage.