What happened
On March 26, 2013, a Jodel D11, registration HB-SUV, was conducting a training flight with an instructor and a student pilot. The flight, which began at Speck-Fehraltorf, was subject to challenging weather conditions, including low clouds and light snowfall. While cruising at approximately 2,500 feet AMSL, the instructor performed a cruise check and attempted to switch the fuel supply from the main tank to the auxiliary tank. During this process, the instructor inadvertently moved the fuel selector to the 'OFF' position instead of the 'AUX' position.
Within about a minute of this manipulation, the engine lost power. The instructor attempted to troubleshoot the issue by checking vital engine controls, including the fuel selector. However, during the attempt to restore fuel flow, the selector was moved too far, further interrupting the fuel supply. With very little altitude remaining above the terrain, the instructor executed an emergency landing in a field northwest of Gossau. The aircraft sustained heavy damage to the airframe and landing gear, but both occupants escaped the wreckage without injury.
The investigation
SUST examined the aircraft's fuel system and the cockpit ergonomics. The investigation established that the fuel selector is located below the instrument panel, making it difficult to see during operation. The mechanism allows the handle to be moved past the intended detents without significant force, which can inadvertently throttle or cut off fuel flow. Furthermore, investigators found that the fuel selector positions in this aircraft were reversed compared to another similar aircraft used by the same flight school, creating a high risk of confusion.
Findings
- The primary cause of the engine power loss was an incorrect manipulation of the fuel selector valve.
- The decision to switch tanks during the cruise check was unnecessary, as there was sufficient fuel in the main tank for the planned maneuvers.
- The low error tolerance of the fuel selector's design contributed to the accident.
- The risk of confusion was heightened because the fuel selector positions were inverted in a second, similar aircraft within the same fleet.
- Adverse weather and low altitude limited the time available to diagnose and correct the fuel interruption.
Safety action
Following the accident, the fuel selector on HB-SUV was replaced with a different model. While the new valve still carries a risk of interrupting fuel flow if moved incorrectly, the labeling has been significantly improved. This modification ensures that the crew can clearly identify which positions allow fuel flow and which positions cut it off.