What happened
On July 13, 1994, a Cessna Centurion 210L, registered as HB-CHZ, departed from Neuchâtel aerodrome for an afternoon scenic flight over the Alps with five passengers. The pilot had foregone the standard fuel dipstick check to avoid noise complaints after noon, relying instead on electrical gauges that indicated approximately 15 US gallons in the right tank and 10 US gallons in the left.
During cruise at 7,000 feet, the pilot noticed the right tank was nearly empty and switched to the left tank. Shortly after, engine power dropped. He engaged the electric fuel pump and switched back to the right tank, restoring power temporarily. Aware the right tank was empty, he switched back to the left tank. Within a minute, the engine lost power again. After switching back to the right tank for a brief moment, he attempted a third switch to the left tank, but the propeller slowed to idle.
Attempting to glide to Bex aerodrome, the pilot found the distance too great due to headwinds. He executed an emergency landing in a beet field near Chessel (Yvorne), deploying no landing gear. All six occupants exited unharmed, though the aircraft sustained significant damage.
The investigation
SUST investigators confirmed the fuel system was mechanically sound with no pre-existing defects. Post-accident inspection revealed the right tank contained only 2–3 deciliters of fuel, while the left held 34 liters. Fuel quality was uncontaminated.
The aircraft’s fuel selector requires passing through a "closed" position to switch tanks, offering no intermediate "both" setting. Flight manual warnings explicitly state that uncoordinated flight (slips or skids) exceeding one minute with tanks at 1/4 capacity or less can uncover fuel outlets, causing starvation.
Findings
The accident was caused by fuel starvation in the left tank due to prolonged uncoordinated flight (a right-skid) while reserves were critically low. This attitude pushed fuel away from the pickup point against the tank wall. Contributing factors included:
- Failure to measure fuel quantity with a dipstick prior to departure.
- Allowing the right tank to deplete almost completely before switching, violating standard cross-feed procedures.
- Inadequate monitoring of fuel consumption during the flight.
- The fuel selector design, which lacks a protected "closed" position and prevents simultaneous tank usage.
Safety action
The report highlighted the critical need for precise fuel measurement via dipsticks rather than gauges alone. It also noted that the specific fuel selector design on this Cessna model poses inherent risks during cross-tank transfers due to the mandatory closed-center position.