What happened
On January 17, 2010, a Dyn’Aero MCR 4 S, registration F-PFSA, departed from the unpaved runway 13 at the Andernos-les-Bains aerodrome. Shortly after takeoff, at an altitude of approximately 400 feet, the aircraft entered a steep left bank and began a nose-down descent. Witnesses observed the aircraft disappear into a nearby forest. The wreckage analysis revealed that the aircraft struck the trees in a steep dive with a magnetic heading of 300°. The pilot and one passenger sustained serious injuries, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and found that the takeoff checklist had been followed, with the flaps retracted and the fuel pump turned off. While the propeller showed deformations indicating a lack of engine power, subsequent bench tests of the engine and electric pump revealed no mechanical malfunctions. Analysis of the fuel in the carburetor confirmed the use of SP 98 unleaded gasoline.
Flight data recorder analysis revealed that the engine experienced two undocumented shutdowns prior to the accident: one at 10:54 local time before alignment, and another at 11:04 local time during engine tests on the club parking area. During the final flight, at approximately 350 feet, the engine RPM dropped from 5,740 to 5,500 before rapidly decreasing until the engine stopped completely. The aircraft then entered an increasing left bank and a nose-down attitude, likely in a right slip.
Meteorological conditions at the time included variable winds of 3 knots and high humidity (87%). Although the pilot did not consult the weather before the flight, observers noted low stratus clouds at the aerodrome. The temperature and humidity levels were identified as being conducive to severe carburetor icing.
Findings
- The primary cause of the accident was an asymmetric stall during an attempted forced landing following an engine failure.
- The engine failure was likely caused by carburetor icing.
- The use of SP 98 fuel, which contains ethanol, may have increased the risk of icing due to its hydrophilic properties.
- The pilot's decision to proceed with the flight despite experiencing two unexplained engine shutdowns earlier that day was a significant contributing factor.