What happened
On 23 May 2014, a private pilot was operating a UFM-10 Samba (registration ZU-CUF) for a local flight departing from Plettenberg Bay aerodrome in the Western Cape. The flight, conducted under visual flight rules in clear weather, lasted approximately 42 minutes before the aircraft landed successfully on the asphalt runway.
While taxiing across the grass apron toward the hangar, the aircraft's nose gear failed. The pilot initially believed the wheel had struck a small, concealed hole in the turf. This failure caused the nose of the aircraft to pitch downward, resulting in the propeller striking the ground. The pilot was able to immediately shut off the master switch and exit the aircraft without injury. The incident resulted in no injuries to the sole occupant, though the aircraft sustained damage to the propeller and the nose gear assembly.
The investigation
SACAA AIID investigators examined the aircraft's maintenance records and the physical evidence of the failure. Although the broken components of the nose gear strut had been discarded by the approved person before a formal metallurgical analysis could be performed, investigators were able to conduct a detailed review of photographs taken of the failed parts.
Technical documentation confirmed that the aircraft was properly maintained and that the pilot held a valid license and medical certificate. While the pilot's account suggested a hole in the apron caused the mishap, airfield personnel reported that the grass had been recently mowed and no significant holes or ditches were present. The investigation focused on the structural integrity of the steel tube assembly of the nose gear.
Findings
Detailed analysis of the photographic evidence revealed that the failure was not caused by an external impact with a hole, but rather by metal fatigue. The investigation established that a crack had initiated at a welded joint on the external nose gear strut. This crack had progressed over an extended period of time, eventually leading to a sudden fracture under normal service loads. The fracture pattern showed a characteristic 45-degree shear lip, indicating a final ductile overstress mode following the long-term fatigue process.