What happened
On January 20, 2010, at 11:26, a Cessna TU206G, registration OH-CHO, was conducting a power line inspection flight near Siilinjärvi, Finland. The aircraft departed from Kuopio aerodrome and reached the inspection site approximately three minutes after takeoff, flying at an altitude between 30 and 90 meters above the ground. To facilitate the inspection, the pilot reduced the airspeed to 80–90 knots, which required a significantly lower power setting than standard cruise flight.
Approximately two minutes into the inspection, the pilot noticed the engine was running unevenly and losing power. Despite attempts to rectify the situation, the engine power could not be recovered. As the airspeed dropped, the pilot was forced to descend further to maintain flying speed. Realizing a crash was imminent, the pilot declared an emergency via radio. The aircraft subsequently performed a forced landing into a forest. While the aircraft was destroyed, the pilot and the passenger, a power line inspector, sustained only minor injuries.
The investigation
Investigators focused on the engine and its associated components. The engine was disassembled, but no mechanical defects or physical damage were found that could explain the malfunction. The aircraft's fuel system was found to be in good working order, and the fuel used was clean and met all required standards. To further investigate, a comparison flight was conducted, simulating the power settings and engine control adjustments used during the accident. During this test flight, no engine malfunctions were reproduced.
Regarding the pilot, the investigation established that the pilot lacked specific training and experience for low-altitude flight and power line inspection operations. The pilot's experience with this specific aircraft type was also considered low, which contributed to a lack of routine and inadequate response during the emergency.
Findings
- The primary cause of the accident was an engine malfunction that resulted in a loss of power, leading to an unprepared forced landing.
- The engine malfunction was likely caused by an overly lean fuel mixture.
- The development of the lean mixture was influenced by the pilot's engine management and the low ambient air temperature.
- The situation escalated into an accident because the pilot failed to enrich the fuel mixture after the engine began to run unevenly.
- A contributing factor was the pilot's lack of specialized training and experience in low-altitude flight operations.
Safety action
- The investigation commission issued a safety recommendation to the operator to revise its training requirements to ensure that all pilots performing low-altitude inspections receive the necessary theoretical and practical training for safe operations.