What happened
On 10 August 2016, a Jodel D1 .40 C Mousquetaire, registration F-BMBX, was performing a private mountain flight at the Vallon du Bergons landing area in Salles-d’Argelès. The pilot, accompanied by a passenger, had completed a reconnaissance of the mountain landing area before attempting a landing on runway 33.
Following a stabilized approach, the pilot executed a three-point landing approximately 40 meters beyond the runway threshold. During the landing roll, as the pilot applied right rudder to maintain the centerline, a loud cracking sound was heard. The aircraft suddenly veered sharply to the left, causing the left wing to break. The aircraft came to rest at the edge of the runway, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and the wing structure to determine the cause of the failure. While the wood used in the wing spar met all manufacturer requirements for quality, the investigation identified high moisture content in the lower rear flange of the left wing spar near the wing-fuselage junction.
An examination of the landing gear revealed that both legs had undergone significant deformation, indicating they had been subjected to abnormally high upward stresses. The shock absorbers were found to be in a degraded state, with reduced functionality and a lack of necessary lubrication. Furthermore, the investigation noted that the aircraft's maintenance program primarily relied on visual inspections and did not require in-depth examinations of the wooden structure or specific measurements of shock absorber travel.
Findings
- The primary cause of the structural failure was the transmission of abnormally high stresses to the wing spar.
- This stress was caused by the insufficient shock absorption properties of the main landing gear due to the poor condition of the shock absorbers.
- The investigation could not rule out the impact of one or more previous hard landings, though the exact timing of such events could not be established.
- The presence of localized moisture in the wing spar area may have contributed to the structural vulnerability, though its exact role in the failure remains unconfirmed.