What happened
On September 14, 2016, a DynAero MCR-4S, registration F-PIMS, was conducting a private flight from Bressaucourt to Yverdon-les-Bains. After an initial leg from Granges to Bressaucourt, the two-pilot crew departed Bressaucourt at 11:05 local time. While the pilot in the left seat handled the takeoff, the pilot in the right seat took control of the aircraft as it approached the Éplatures control zone.
During the descent toward Yverdon, at approximately 11:30, the aircraft was near the locality of Champagne at 3,700 ft AMSL when the engine experienced a brief hiccup followed by a complete loss of power. The pilot in the left seat activated the electric fuel pump and issued an emergency message to the Yverldon aerodrome frequency. Due to the loss of power and the high aerodynamic drag caused by the propeller being at a low pitch, the crew determined they could not reach the paved runway at Yverdon. The pilot in the right seat subsequently performed an emergency landing in a mown field north of Valeyres-sous-Montagny. There were no injuries to the crew or the passenger, and the aircraft sustained no damage.
The investigation
Technical examinations of the aircraft were conducted at Payerne. Investigators found that the fuel filters were clean, the oil level was within normal limits, and the engine and propeller systems showed no mechanical defects. The fuel system and powerplant were functional, and the engine was able to run during tests once the battery was recharged.
Data from the aircraft's Dynon FlightDEK-D180 electronic flight information system (EFIS) provided critical insights. The records showed that the fuel level in the left wing tank had been dropping steadily, but in the three minutes preceding the engine failure, the fuel level dropped sharply and began to fluctuate. Flight data also revealed that while the aircraft had been flying in a coordinated manner initially, it had entered a state of slip (left wing down) during the descent.
Findings
The investigation established that the engine failure was likely caused by fuel starvation. At the time of the incident, the left wing tank was only partially full. Because the aircraft was flying in a slip with a slight left bank and a negative nose pitch, the remaining fuel likely pooled in the outer forward section of the tank. This movement of fuel prevented it from reaching the fuel outlet, effectively cutting off the supply to the engine. The pilot in the right seat likely did not notice the slip because the cockpit geometry obscured the visibility of the slip indicator (the ball) on the EFIS, which was positioned on the left side of the cockpit.