What happened
On the evening of March 14, 2003, a pilot operating an amateur-built Jodel D 112, registration F-PIHH, departed from Grenoble-Le Versoud for a local flight toward the Belledonne massif. Due to the late hour, the pilot was unable to refuel at the airfield's fuel station. Before takeoff, the pilot estimated a flight endurance of approximately 1 hour and 45 minutes based on recent consumption trends and a visual check of the fuel gauge.
During the flight, the pilot climbed to 10,000 feet, flying "on top" of a cloud layer. As the cloud layer became continuous, preventing a direct descent, the pilot had to plan a longer route to bypass the clouds to the northwest before returning to the airfield. While descending at a steep angle to penetrate the cloud layer, the pilot activated the carburetor heat. At this stage, the pilot estimated 45 minutes of remaining endurance, despite the fuel gauge having indicated zero for ten minutes.
Shortly after, the engine stopped. The pilot broadcast a fuel exhaustion emergency on the Grenoble Saint-Geoirs frequency. Despite attempts to restart the engine, the power loss persisted, forcing a landing in a field. During the landing, the aircraft experienced a ground loop, causing minor damage to the landing gear and propeller.
The investigation
Investigators examined the aircraft's fuel system and the fuel gauge mechanism. The gauge utilized a float on a rigid rod that extended through the engine cowling. It was determined that the gauge indicated "zero" while approximately 12 liters of fuel remained in the tank.
Testing revealed a design flaw in the vent system: at low fuel levels, the cap on the gauge rod could obstruct the vent tube, preventing proper airflow. This obstruction could stop fuel from flowing via gravity to the carburetor. While the engine failure might have been triggered by the steep descent causing fuel starvation, the investigation noted that the remaining fuel volume was insufficient to safely complete the extended flight path regardless of the mechanical failure.
Findings
- The pilot decided to proceed with the flight with a fuel quantity that provided no safety margin given the prevailing weather conditions.
- Inadequate monitoring of changing weather conditions led to an unplanned extension of the flight duration.
- A late decision to return to the airfield contributed to the exhaustion of usable fuel.
- The design of the fuel gauge provided an inaccurate representation of remaining fuel at low levels.
- The aircraft's flight attitude during descent may have caused fuel starvation, while the vent obstruction likely prevented a successful engine restart.