What happened
On July 21, 2016, a Fournier RF47, registration F-GSTJ, was conducting a private flight from Carpentras toward the coast. The aircraft was carrying a pilot and one passenger. Approximately 45 minutes into the flight, while cruising at 900 feet, the pilot switched the fuel selector from the left tank to the right tank. Shortly after this maneuver, the engine experienced a significant drop in power accompanied by unusual coughing noises.
Despite the pilot attempting to restore power by activating the electric pump and switching back to the left tank, the engine power continued to decline. Unable to maintain level flight, the pilot issued a distress message and performed a forced landing on an unoccupied beach near Les Saintes-Maries-de-la-Mer. During the landing roll, the nose gear struck a rock hidden beneath the sand, causing the gear to break and resulting in heavy damage to the Fournier RF47.
The investigation
The BEA examined the wreckage and the engine's maintenance history. Investigators confirmed that both fuel tanks contained sufficient, uncontaminated fuel and that the fuel delivery system to the carburetors was intact. While no mechanical breakage was found in the engine, evidence of overheating was present on the cylinder heads and valves. The investigation revealed that the cylinder seals were ineffective, leading to unacceptable leakage rates and low compression.
Analysis of the engine oil showed high water content and the presence of metallic elements, indicating wear within the lubrication circuit. The investigation also noted that the pilot and passenger had previously experienced warm air flowing near their feet during flights, which was identified as a symptom of the engine operating at abnormally high temperatures.
Findings
- The engine power loss was caused by the poor condition of the engine, which resulted from operating at abnormally high temperatures.
- The primary cause of the overheating was the use of an inappropriate mineral oil.
- The engine manufacturer's maintenance manual contained ambiguous instructions regarding oil selection, stating what types of oil should *not* be used rather than explicitly prescribing the required type. This ambiguity led to the use of a mineral oil that was not suitable for the engine's requirements.