What happened
Following the installation of a new fuel valve, a mechanic placed 10 gallons of fuel in each wing tank to facilitate testing and installation procedures. Before takeoff, the pilot filled the right fuel tank but did not visually verify the amount of fuel remaining in the left tank.
The pilot conducted taxi and runup procedures for approximately 15 minutes with the left fuel tank selected. After completing the takeoff, the engine lost power once the aircraft reached an altitude of 300 feet. Upon the loss of power, the pilot switched to the right fuel tank, which restored some engine power. Due to the low altitude, the pilot focused on performing a forced landing.
The investigation
An examination of the engine revealed no mechanical failures. Investigators determined that the left fuel tank contained 15 gallons of fuel at the time of the incident. It was noted that the left wing tip was resting on the ground and that the fuel tanks interconnect through the fuel valve even when the valve is in the off position.
Findings
The aircraft owner's operating manual includes a pre-takeoff checklist stating that the fuel selector should be set to the tank containing the greatest amount of fuel.