What happened
On July 19, 2016, a Jodel D 140 R, registration HB-SFR, was performing a VFR flight from La Côte to the mountain landing site at Croix de Coeur in the Valais region. The flight involved two occupants and followed a pattern of several landings at the site. After completing two successful reconnaissance passes and a brief pause, the aircraft departed for a third landing.
During the approach, the aircraft touched down at the very beginning of the landing area. While the initial contact was described as normal, the left landing gear suddenly collapsed. This failure caused the aircraft to veer sharply to the left, executing a 120-degree rotation around its yaw axis. The aircraft slid 54 meters from the initial contact point before coming to a halt. Despite the impact, there was no fire, and both the pilot and the passenger were able to exit the aircraft uninjured.
The investigation
Investigators examined the wreckage and the mechanical components of the landing gear. The inspection of the left main gear revealed that the wheel axle had fractured at the weld bead of the brake caliper mounting flange.
Metallurgical analysis of the axle was performed to determine the nature of the failure. The examination of the fracture surface showed two distinct characteristics: a brittle fracture covering approximately three-quarters of the circumference and a ductile shear fracture on the remaining quarter. The investigation also noted traces of corrosion on the internal wall of the axle.
Findings
- The primary cause of the accident was the brittle failure of the left wheel axle.
- The brittle state of the metal was a result of a change in crystalline structure that occurred during the solidification process of the weld used to attach the brake caliper support.
- This pre-existing embrittlement was likely further compromised by long-term internal corrosion within the axle.
- The final rupture was triggered by excessive stress applied to the weakened axle during the touchdown on the sloped terrain.
- The structural weakness was not detectable during standard pre-flight inspections.