What happened
On August 4, 2017, at 17:39 local time, a Cessna 337G, registration EC-GPQ, operated by Sociedad Aeronáutica Peninsular, performed an emergency landing in a field near Belver de los Montes, Zamora. The aircraft was engaged in aerial coordination and observation duties for wildfire suppression near Verín, Ourense.
During the return flight to Valladolid Airport, the aircraft's rear engine stopped operating. The pilot attempted to restart the engine without success and subsequently feathered the propeller. Due to a progressive loss of altitude caused by operating on a single engine—compounded by high ambient temperatures of 40°C and the aircraft' and crew weight—the pilot determined that maintaining level flight was impossible and executed a controlled emergency landing in a field covered with brush.
All four occupants (the pilot and three crew members) were uninjured. The aircraft sustained damage to the lower fuselage and the propeller tips of the front engine.
The investigation
The investigation focused on the fuel system and flight management. Post-incident inspections revealed that the right fuel tank was completely empty, while the left tank contained 28 liters. Crucially, the cockpit fuel gauge had indicated approximately 60 gallons remained in the right tank at the time of the engine failure.
Technical examination of the fuel system identified a fault in the right tank's indication system. A damaged ground wire (black) at a solder point on the white wire from the tank sensor was causing a short circuit, which provided a false high reading of the fuel level.
Furthermore, the investigation analyzed the pilot's pre-flight and in-flight procedures. It was determined that the pilot had relied on an estimate of fuel endurance rather than a physical visual check of the tanks, and failed to follow the operator's standard procedure of checking fuel levels every 30 minutes during flight.