What happened
On November 4, 2013, a Cessna TU 206G, registration OK-TSK, was performing a recreational flight near the Ratmírovský pond when the engine suddenly failed. The pilot, who was flying with one passenger, reported experiencing vibrations and a heavy impact from the engine compartment, followed by visible smoke.
Following the engine failure, the pilot identified a suitable landing area in a field approximately 1 km southeast of the village of Hospříle. The terrain consisted of soft, clay-like soil covered in winter rape crops. During the emergency landing, the aircraft's propeller struck the ground, and the tip of the right wing made contact with the terrain. While the crew escaped the aircraft without injury, the impact caused significant structural damage to the wing, the cabin roof, and the propeller.
The investigation
The ÚZPLN investigation focused on the mechanical failure of the Continental TSIO520 M6B engine and the operational status of the pilot. Technical examination of the engine revealed extensive internal damage, including the failure of the connecting rod eye of the second cylinder and the destruction of cylinder linings.
Investigators also reviewed the aircraft's maintenance history and the pilot's qualifications. It was noted that the aircraft was frequently used for high-stress parachute deployment operations, which involve frequent takeoffs at maximum takeoff weight and high-power climbs. Additionally, the investigation found that the pilot was operating with an expired SEPland qualification, having exceeded the validity period by more than two months.
Findings
- The primary cause of the accident was an engine failure caused by the seizure of the connecting rod bearing due to a failure in the main crankshaft bearing.
- The failure of the main bearing led to the obstruction of the oil supply channel for the second cylinder's connecting rod, resulting in rapid overheating and seizure.
- The engine had been subjected to high-stress flight profiles typical of parachute operations, which are difficult to maintain at optimal thermal conditions.
- Maintenance records showed that the interval for an oil change following an engine overhaul had been exceeded by 50%.
- The passenger was seated in a modified area of the cabin not designed for safe transport and was not restrained, which posed a risk of shifting the aircraft's center of gravity during maneuvers.
- The pilot was not legally authorized to act as commander at the time of the flight due to an expired qualification.