What happened
On September 9, 2006, a Robin R 2120 U, registration F-HAPC, departed from Lognes airfield for a flight. During the climb, as the aircraft reached approximately 1,000 feet, the engine experienced a significant loss of power. The pilot attempted to maintain airspeed by advancing the throttle to its limit, but was unable to maintain level flight and was forced into a descent.
After notifying air traffic control that a return to the airfield was impossible, the pilot performed an emergency landing in an uncultivated field approximately six kilometers east of Logn0es. During the landing roll, the landing gear collapsed, causing the aircraft to come to a stop in a ditch. The impact resulted in extensive deformation to the wings and fuselage, though the engine and propeller remained intact.
The investigation
The investigation focused on the cause of the engine power loss. While engine tests on a test bench showed no malfunctions, radio communications analysis confirmed a measurable drop in engine RPM during the flight.
Upon examining the carburetor, investigators discovered an anomaly within the hollow polymer float. One of the two independent float chambers, which should have been empty and airtight, had become partially filled with fuel. This ingress of fuel altered the float's buoyancy and balance, creating asymmetrical forces on the hinge. This imbalance hindered the free movement of the float and the needle valve, leading to an inconsistent fuel level in the float bowl and a subsequent change in the fuel-air mixture richness.
Findings
- The primary cause of the power loss was a malfunctioning carburetor float.
- Fuel had leaked into one of the hollow chambers of the polymer float, disrupting the regulation of the fuel level.
- The manufacturer had previously issued service information letters regarding this specific type of float, but the information was not widely disseminated by primary aviation authorities.
- There was a lack of effective communication between manufacturers and regulatory bodies like EASA and DGAC, meaning many operators were unaware of the specific risks associated with this component.