History of the Flight
On 13 September 2020, a pilot from Aéroclub de Pamiers les Pujols prepared a Robin DR400-160 (registration F-GMRV) for an introductory flight with three passengers. The pilot estimated that three of the four fuel tanks were half full, totaling approximately 80 litres, which he believed provided about three hours of flight time. The aircraft took off from Pamiers les Pujols aerodrome at approximately 15:45 local time and headed south to fly over the Cathar castles.
After about 25 minutes, while flying at 6,500 ft near Montségur Castle, the pilot observed an intermittent reduction in engine power and saw indicator lights illuminate on the warning bar, though he could not recall which ones. He operated the electric pump and stated that he switched from the main tank to the LH auxiliary tank, but the issue persisted. Considering the terrain suitable for a forced landing, the pilot turned toward an upsloping, obstacle-free area, extended flaps, closed the fuel selector, and just before touchdown set the mixture to idle cut-off and cut the magneto contacts. The aircraft touched down, bounced, and rolled about 20 metres before stopping, with all three landing gears broken.
Aircraft Information
The aircraft was equipped with a Lycoming O-320 160 hp engine that had 2,098 flight hours since last overhaul. It had 17 flight hours since the last maintenance inspection and was within its weight and balance envelope. The DR400-160 has four fuel tanks: a main tank (110 L), two wing tanks (40 L each), and an optional additional tank (50 L). The additional tank was not normally used by the club and contained no fuel. The pilot believed the main tank and both wing tanks each held about half their capacity. Estimated fuel consumption for the 28-minute flight was about 20 litres.
Examination of Site and Wreckage
The accident site was on a low mountain slope. The first impact was about 20 metres from the wreckage. Propeller damage was consistent with lack of power at landing. The fuel selector was found blocked in the closed position. Post-accident fuel measurements showed the LH wing tank contained 0.6 litres, the RH wing tank about 15 litres, and the main tank 74 litres. The tanks were not deformed or leaking. Engine bench tests showed nominal performance when supplied with fuel.
Pilot Information
The 79-year-old pilot held a Private Pilot Licence (Aeroplanes) with approximately 4,500 flight hours, 77 of which in the last three months on type. He also held a mountain rating.
Meteorological Information
Météo-France estimated conditions at the site: south-south-westerly wind, calm at valley bottom, light slope breeze, CAVOK, temperature 21°C, dew point 12°C, QNH 1021.
Statements
The pilot stated that he had flown on the main tank fuel selector position throughout the flight, then switched to the LH wing tank activating the electric pump, and closed the selector before landing. The pilot and front passenger recalled indicator lights on the warning panel during the power reduction but could not specify which ones. The pilot did not consider fuel depletion at any time.
Conclusions
The lack of fuel in the LH tank and the engine's correct operation on the test bench led to the conclusion that the engine stopped due to unpriming of the fuel system from fuel depletion of the LH wing tank. These observations contradicted the pilot's statement that he had used the main tank. It is very likely that the low fuel level warning for the LH front tank activated during the flight.