What happened
During a preflight inspection, the pilot noted that the fuel tanks were filled to the bottom of the filler neck and considered this an appropriate level. After the engine was started, fuel began leaking from the fuel sump drain hose. The pilot addressed this by operating a spring-loaded valve handle inside the aircraft, which stopped the leak.
Shortly after departure, the engine began running roughly, prompting the pilot to deviate toward another airport. During this period, the engine performance returned to smooth operation, and the pilot continued toward the original destination. However, during the descent phase, the engine again began running roughly. The pilot determined that the fuel tanks had been exhausted and executed a forced landing. The aircraft sustained substantial damage.
The investigation
An investigation into the flight duration and fuel capacity revealed that while the aircraft's cruising endurance at 75% power with 90 gallons of fuel is 5.4 hours, the usable fuel capacity when tanks are filled only to the bottom of the filler necks is approximately 80 gallons. The actual flight time for this mission was 5.55 hours.
A Federal Aviation Administration inspector examined the aircraft and found no leaks in the fuel system. Only residual fuel was discovered within the selector valve.