What happened
On 16 November 2008, a private flight departing from Kitty Hawk Aerodrome experienced a mechanical failure during the takeoff roll. As the Cessna 206, registration ZS-OXI, rotated, the pilot noted a distinct shudder originating from the left-hand landing gear. Following one circuit of the airfield, the pilot elected to return to the aerodrome to inspect the issue.
Upon landing on Runway 01, the vibrations intensified. While the pilot attempted to maintain directional control and bleed off airspeed, the left-hand main undercarriage collapsed. This caused the aircraft to veer left and come to an abrupt stop approximately 150 metres before the end of the runway. There were no injuries to the pilot, though the aircraft sustained minor damage to the left-hand horizontal stabilizer and the undercarriage assembly.
The investigation
SACAA AIID investigators examined the fractured components of the undercarriage assembly, specifically the inner and clamp brackets and associated bolts. Metallurgical analysis was performed on the left and right-hand main undercarriage assemblies to determine if a single high-load event caused the failure.
The investigation also reviewed the aircraft's history, noting that ZS-OXI had been involved in two previous forced landings on uneven, ploughed terrain due to engine failures. Investigators looked for evidence of whether the undercarriage bolts had been replaced or improperly serviced following those earlier incidents.
Findings
Technical analysis revealed that the failure was not caused by a single, singular overload during the landing at Kitty Hawk. Instead, the metallurgical evidence pointed to a low-cycle, high-strain fracture of the left-hand inner bracket attachment bolt. The bolt showed signs of potential over-torque or the use of incorrect tools during installation.
It is believed that the structural integrity of the bolts may have been compromised during the aircraft's previous forced landings on uneven terrain. The investigation concluded that the left-hand bolt sheared over an undetermined period, eventually allowing the undercarriage arm to move outward, which caused the subsequent collapse and damage to the clamp bracket and fuselage. The right-hand assembly was also found to have experienced a comparable failure mode due to the resulting strain.