What happened
On July 12, 2001, at approximately 07:07 local time, a Cessna U206A, registration OH-CSU, experienced a major engine failure while climbing through roughly 800 meters near Utti, Finland. The aircraft was conducting its third jump flight of the morning as part of a Finnish Defence Forces parachuting training camp.
During the climb, the engine began to vibrate violently, accompanied by a drop in oil pressure and an increase in engine temperature. Smoke was observed emanating from the lower center of the instrument panel. The five skydivers on board, aware of the developing situation, decided to perform an emergency jump. Although the aircraft's jump door had a known mechanical issue with its sliding pin, the crew was able to open it sufficiently to exit the aircraft. The skydivers exited the plane at an altitude of approximately 600 meters and landed safely in a field north of the drop zone.
Following the jumpers' exit, the pilot shut down the engine and transitioned to a glide. The pilot maintained a target airspeed of approximately 90 knots and steered the aircraft toward runway 07. Despite the engine failure, the pilot successfully executed a steep left turn and landed the aircraft on the active runway.
The investigation
The investigation focused on the mechanical failure of the engine and the subsequent damage. Investigators examined the engine components, including the crankshaft and oil system. Metallurgical analysis was conducted by the Technical Research Centre of Finland (VTT) to examine the fracture surfaces of the connecting rod components. The investigation also reviewed the maintenance history of the engine, noting that it was nearing the end of its scheduled overhaul interval, with only 23 flight hours remaining before a required overhaul.
Findings
- The primary cause of the engine failure was a fatigue fracture in the number 2 connecting rod.
- The failure of the connecting rod released metal debris into the engine's lubrication system.
- This debris clogged the oil pump suction strainer, which subsequently led to bearing damage and the failure of the number 3 bearing.
- The investigation noted that the engine had completed 1,677 hours since its last overhaul, leaving very little time before the next mandatory inspection.
- The pilot and the skydivers acted effectively and safely during the emergency.