What happened
On June 12, 2003, a Rans S 12 Airaile ultralight, identified as 33-RK, was returning to the Carcans airfield in France following an aerial photography mission. While flying at an altitude of approximately 500 feet, the pilot noticed that the engine coolant temperature had reached its maximum reading. Suspecting a faulty instrument rather than an actual mechanical issue, the pilot continued the flight.
Shortly after this observation, the Rotax 5ered engine ceased operation, and the propeller stopped rotating. Faced with a total loss of power, the pilot was forced to perform an emergency landing in an uncultivated field characterized by numerous tree stumps. During the landing sequence, the aircraft flipped onto its back and came to a rest.
The investigation
The investigation focused on the mechanical failure of the engine and the circumstances leading to the loss of power. Investigators examined the engine, which had only approximately 15 hours of total operating time since being purchased new. The inspection of the cooling system revealed that a connection sleeve in the coolant circuit had become detached.
Findings
- The primary cause of the engine failure was a significant coolant leak caused by the detachment of a cooling circuit fitting.
- This leak led to rapid engine overheating, which subsequently caused the engine to seize.
- The pilot's decision to continue the flight after noticing high temperature readings contributed to the engine failure occurring mid-flight.