Cessna 206G Forced Landing in Bushbuckridge Area

Flight Details and Accident Sequence On 12 December 2010, a Cessna 206G, registration ZS-OYV, departed Hoedspruit Civil Aerodrome (FAHT) at 0603Z for a private flight to Kruger Mpumalanga International Aerodrome (FAKN). The aircraft was operated by Baeti Investments (PTY) LTD and was flying under visual meteorological conditions. While en route over the Bushbuckridge area, the aircraft experienced a total engine failure. The pilot attempted to restart the engine unsuccessfully and subsequently executed a forced landing in an open, grass-covered area identified from the air. The pilot, the sole occupant, was not injured. Damage was sustained to the nose landing gear, propeller, and a cargo pod installed on the lower fuselage. No pre- or post-impact fire occurred, and the accident was considered survivable due to low kinetic forces. The pilot was wearing a safety harness during the flight. ## Aircraft and Pilot Information The aircraft, a 1978 Cessna U206G with serial number 206-04349, had 4,729.2 airframe hours at the time of the accident. The engine was a Continental IO-520-F with 2,957.6 hours since new. The pilot was a 47-year-old South African male holding a valid private pilot licence with 3,414.7 total flying hours and 187.4 hours on type. The pilot's medical certificate was valid until 30 September 2011, with a restriction for corrective lenses. The last mandatory periodic inspection was certified on 14 May 2010. ## Investigation Findings and Probable Cause No on-site investigation was conducted, and no wreckage or impact information was available from the scene. Following recovery, the engine was removed and forwarded to an approved maintenance facility for a teardown inspection. The inspection revealed that the crankshaft had failed. Observations included lateral damage to several bearings and evidence that the bearings had moved within their respective journals. Photos of the failed crankshaft and main bearings were forwarded to the engine manufacturer for an expert opinion. The manufacturer noted mechanical fretting on the main bearing journal face and elongation of the main bearing journal lock slot, indicating that the crankcase through bolts were in an under-torque situation. This under-torque condition allowed the bearings to shift forward and aft, leading to contact with the journal radii, heat collection, and ladder cracking. The manufacturer stated that this type of separation is routinely observed when crankcase fretting and under-torqued through bolts are present, often following cylinder removal for maintenance within the last 200 flight hours. The failed crankshaft was not sent for metallurgical analysis, as the manufacturer indicated this failure mode is known to occur when bearing movement has occurred. The probable cause was determined to be an unsuccessful forced landing following an in-flight engine failure attributed to a mechanical failure (crankshaft failure).