What happened
On 19 July 2008, an Avions Pierre Robin DR40 and registration F-GDYD was conducting a private flight as part of a seven-day journey from Chavenay, France, to the United States. While transiting over North Wales, the aircraft was flying at approximately 2,500 to 3,000 feet to avoid cloud cover. During the flight, the pilot had transitioned the fuel supply to the left wing tank.
As the aircraft moved north of Welshpool, the engine suddenly lost power, with the RPM dropping to 1,500. The crew attempted to restart the engine by activating the electric fuel pump and switching the fuel selector, but the engine failed to accelerate. Despite applying carburettor heat, the engine remained non-operational. The pilot identified a suitable field near Llanfihangel Glyn Myfyr for an emergency landing. During the approach, the aircraft touched down in a field, but the momentum caused the aircraft to yaw into a bank and strike large boulders, resulting in substantial damage to the airframe. Both crew members sustained serious injuries.
The investigation
The AAIB examined the wreckage and analyzed data from several GPS units and radar heads. The investigation focused on the fuel system, the carburettor, and the atmospheric conditions. Examination of the fuel system showed no blockages or defects in the wiring or components. While the carburettor bowl was found to be dry, there was no evidence of a pre-impact blockage in the intake.
Testing of the fuel system demonstrated that while the system could generally re-prime itself, the presence of air in the lines could occasionally create an airlock, preventing fuel from reaching the carburettor. Meteorological data indicated that the area was experiencing a Polar Maritime airflow with temperatures and humidity levels highly conducive to carburettor icing.
Findings
- The engine failure was likely caused by fuel starvation, as the usable fuel in the left wing tank had been exhausted.
- The lack of a fuel low-pressure warning light prior to the failure was noted, though the crew did not recall seeing it.
- Atmospheric conditions were highly conducive to serious carburettor icing, which may have prevented the engine from restarting even if fuel supply had been restored.
- The hilly terrain and the necessity of flying below cloud base left the crew with very few options for a safe landing site.