What happened
On April 16, 2018, a Pipistrel Virus SW112, registration F-HOCR, was conducting a local training flight near Saint Léger en Yvelines, France. The flight, operated by an ATO, involved an instructor and a student pilot performing climbing and descending exercises west of the Rambouillet forest. During a simulated avoidance maneuver involving a descent, the crew experienced engine misfires and a subsequent loss of engine power. No cockpit alarms were triggered.
After the student pilot attempted to manage the situation, the instructor took control of the aircraft. The student declared an emergency on 121.500 MHz and set the transponder to 7700. The instructor identified a suitable field for an emergency landing. While the landing itself was successful, the aircraft encountered a height difference of approximately 50 cm between the landing area and the adjacent field during the landing roll. Despite braking attempts, the aircraft struck an embankment, causing the nose gear and left main gear to collapse and damaging a propeller blade.
The investigation
The BEA examined the wreckage and the engine components to determine the cause of the power loss. The investigation focused on the engine's Rotax 912-S3-01 unit and the presence of any contaminants in the fuel or air systems. Physical examination of the wreckage revealed that the nose gear and left main gear were broken, and a propeller blade was damaged.
Upon inspection of the engine, investigators found no mechanical failures within the engine itself. However, laboratory analysis of the left carburetor's air intake filter revealed an abnormal pink coloration. This color matched the chemical composition of the engine's coolant. Furthermore, traces of pink liquid were found sprayed across the upper left portion of the engine and the interior of the engine cowling. The coolant expansion tank was also found to be nearly empty.
Findings
- The primary cause of the engine power loss was a continuous leak of coolant from the radiator cap.
- The leaking coolant entered the left carburetor, altering the air-fuel mixture and causing the engine to lose power.
- Although the coolant level was depleted, the engine's cooling system continued to operate within normal temperature ranges during the flight.
- The crew correctly executed engine failure procedures, and the instructor successfully performed the emergency landing.
- The structural damage to the Pipistrel Virus SW121 was caused by the aircraft striking an embankment during the landing roll.