What happened
During a routine local flight at the Cerfontaine airfield (EBCF), a Henri Mignet HM 203 (registration 59CKF) experienced a catastrophic landing gear failure. The flight, which was a second test mission following repairs from a previous incident, proceeded normally until the final approach.
As the aircraft touched down, the nose wheel and fork assembly separated from the landing gear leg at the moment of ground contact. This separation caused the nose landing gear leg to strike the runway grass, creating a 3.5-meter track. The sudden deceleration forced the engine into the ground, causing the aircraft to flip over. While the pilot sustained a concussion and facial injuries, they were able to exit the wreckage unassisted. The impact also caused the fuel tank to puncture and leak, though no fire occurred.
The investigation
Investigators examined the broken nose wheel fork and the material used in its construction. The aircraft was a homebuilt model, and the pilot had recently replaced the nose gear fork with a part they manufactured themselves.
Technical analysis revealed that while the pilot intended to use a specific 25CD4S steel, they instead used a material labeled as "Stub" steel provided by a vendor. Investigation of the vendor's catalog showed that this "Stub" steel was not an equivalent substitute for the required specification and was explicitly noted as being unsuitable for welding.
Furthermore, the investigation looked into the failure of the shoulder harnesses. The leather straps, which were sourced from non-aviation origins, snapped at their attachment points during the impact, allowing the pilot's head to strike the instrument panel.
Findings
- The primary cause of the accident was the failure of the nose wheel fork.
- The component failed because the material used for the replacement part did not meet the original designer's specifications.
- The use of unverified "Stub" steel, which lacked the necessary properties for the assembly, led to the mechanical breakage.
- The shoulder harnesses failed to restrain the pilot due to insufficient strength and the use of non-aviation grade leather straps.