What happened
On June 1, 2001, a Robin DR 400 - 120, registered F-GJZJ, was conducting a cross-country flight departing from Toulouse Lasbordes. After approximately ten minutes of level flight at 2,000 feet, the pilot attempted to climb to Flight Level 5500. During this power increase, the engine failed to deliver the required power, operating at a reduced RPM that was insufficient to maintain level flight.
While in radio contact with Toulouse Information, the pilot declared an emergency and prepared for an off-airport landing. The aircraft subsequently performed a forced landing in a plowed, uphill field near Le Faget. The landing resulted in no injuries to the two occupants on board. A passing pilot eventually alerted air traffic control to the aircraft's location.
The investigation
The investigation focused on the engine's failure to respond to throttle inputs. Investigators examined the fuel system and the carburetor to identify any potential contamination. While fuel samples taken from the carburetor bowl and the fuel circuit were found to be standard 100LL aviation gasoline with no anomalies, a physical inspection of the carburetor revealed a blockage.
Findings
Investigators discovered that the main jet's inlet orifice was partially obstructed by a soft, translucent substance. Laboratory analysis identified this material as silicone, matching the composition of the firewall partition gasket. The flexible nature of the silicone allowed enough fuel to pass through to maintain low-power operation, but the material shifted to cause a significant blockage when the pilot requested higher fuel flow during the climb. It was determined that this silicone debris entered the carburetor during a previous maintenance intervention, as the existing fuel filters were functioning correctly and would have otherwise prevented such contamination.