What happened
Approximately 5 hours and 13 minutes into a cross-country flight, the airplane's engine lost power. This loss of power was caused by fuel exhaustion. Following the engine failure, the pilot performed a forced landing, during which the aircraft touched down on the up-slope of a sand dune.
Prior to the departure, the pilot reported that an inspection of all four fuel tanks had been completed following refueling. At approximately 3 hours into the flight, the pilot conducted fuel calculations based on readings from the fuel gauges, estimating a fuel usage rate of 12 gallons per hour (gph).
The investigation
Investigation into the aircraft's fuel capacity revealed that the four fuel tanks had a total capacity of 84 gallons, with 80 gallons being usable. While the pilot's estimate during flight was 12 gph, the operator reported that the normal fuel consumption for the aircraft is between 15 and 18 gallons per hour. Data from the two previous flights indicated an average fuel consumption rate of 16.27 gallons per hour.