Primary finding
Probable cause
The pilot's inaccurate fuel consumption calculations which led to fuel exhaustion and subsequent loss of engine power.
Investigator assessment
Analysis narrative
The pilot incorrectly calculated the fuel consumption for the planned flight to be 3.3 gallons per hour (gph), instead of 5.4 gph as referenced in the operator's manual. After takeoff with a full 10-gallon fuel tank, the pilot flew for approximately 1 hour then turned to return. At that time the fuel gauge showed "1/2" tank. During the return leg, the pilot noticed the fuel quantity gauge was indicating approximately "1/4" tank. He diverted towards a nearby airport, but the engine experienced a total loss of engine power. While descending for the forced landing, the airplane collided with a tree. Examination of the wreckage revealed that the fuel tank remained intact and was absent of fuel.
Source record
Factual narrative
The pilot stated that he filled the amateur-built Challenger II airplane's 10-gallon fuel tank before departure, and he uses approximately 3.3 gallons per hour (gph) in his fuel consumption calculations. After takeoff, he flew for about 1 hour, and then elected to return to the departure airport. At that time, the fuel quantity gauge indicated "1/2" remaining. The flight continued, and at an unknown time, the fuel quantity gauge indicated "1/4" remaining. He diverted towards a nearby airport, but the engine experienced total loss of engine power. While descending for a forced landing, the airplane collided with a tree. Examination of the airplane by a Federal Aviation Administration inspector revealed the fuel tank was empty. It was not breached and there was no evidence of fuel leakage. The Rotax "Operators Manual" indicates fuel consumption to be 7.0 and 5.4 gph at takeoff and 75 percent continuous power, respectively.