Accident Overview
On 6 April 2018, at approximately 12:10 local time, a Robin DR400-160, registered as F-GCUI, operated by Aéroclub de l'Avallonais, was taking off from runway 04 at Avallon aerodrome (Yonne, France) for a local pleasure flight with the pilot and three passengers. Shortly after becoming airborne, the pilot perceived a loss of engine power and the aircraft began to lose altitude. The pilot kept the throttle at full power with his left hand and turned left to land in a dirt field adjacent to the aerodrome, roughly aligned with the takeoff axis. During the turn, the aircraft struck a tree and then impacted the ground. The pilot and the three passengers sustained serious injuries, and the aircraft was destroyed.
Examination of the Wreckage and Engine
Examination of the crash site, located about 150 m from the opposite runway threshold in an uncultivated field, showed that all flight controls were continuous and functional at the time of impact. Due to wing destruction, the flap position could not be precisely determined. Engine examination indicated that it was running but delivering little power at impact; the throttle controls were found in the idle position. The engine was examined at the BEA and no mechanical anomaly was found. The electrical harness and magnetos showed no failures.
The carburetor was removed for testing. Tests revealed that:
- Fuel consumption was particularly low.
- The installed carburetor jet was deformed, restricting fuel flow. The origin of this deformation, which predated the accident, could not be determined.
- The jet was also partially obstructed by impurities of likely endogenous origin.
Fuel consumption remained low after cleaning the impurities. It returned to nominal values only after the deformed jet was replaced with an identical serviceable jet.
Pilot Information
The pilot, aged 73, held a Light Aircraft Pilot Licence (LAPL(A)), issued in October 2017 after conversion from a basic license obtained in November 2012. He had a total of 92 flight hours, of which 45 as pilot-in-command, almost all on F-GCUI.
Weather Conditions
Meteorological conditions at the time, as estimated by Météo France for Avallon aerodrome, included no clouds below 1500 m, visibility greater than 10 km, temperature 15 °C, wind from south-southeast at 7 kt, and no precipitation.
Pilot's Account
After arrival at the aero club, the pilot and passengers removed the aircraft from the hangar and performed a pre-flight inspection. The pilot checked that the fuel selector was in the central position. The wing tanks were empty, and the central tank was half full, providing sufficient endurance. He checked the runway condition and seated the passengers to achieve balanced center of gravity. Engine run-up revealed no issues. During takeoff roll, engine RPM and ground acceleration appeared normal. He rotated at about 110 km/h, and the climb gradient was as usual.
Abruptly, the pilot felt a loss of engine power without warning, accompanied by an unusual engine noise. He told passengers the engine was lacking power. Seeing the aircraft not gaining altitude, and to avoid industrial buildings ahead, he turned left aiming for an emergency landing. He kept the throttle full forward with his hand until impact. The aircraft struck the top of a tree and then pitched down, rolling inverted. The pilot evacuated and tried to free the passengers, but due to eye burns (likely from fluid projection) could not release all; he walked to the aero club to alert emergency services.
Conclusions of the Investigation
Shortly after takeoff, the pilot experienced an engine power reduction. BEA examinations could not precisely determine the causes of this power loss, but established two contributing conditions:
- The carburetor jet was deformed, restricting fuel flow.
- Unexplained endogenous contamination was present in the jet channel, further limiting flow.
Since previous flights showed no notable anomalies, it is possible that additional particles agglomerated in the jet at takeoff, leading to an air/fuel mixture lean enough to reduce power. This event was likely due to the combination of carburetor contamination by impurities and a defective jet, without the contribution of each factor being clearly established.