Incident Overview
A pilot reported that the aircraft departed with 120 gallons of usable fuel on board. Approximately one hour into the flight, while cruising between 2,000 and 2,500 feet mean sea level and using fuel from the main tank, the pilot activated the boost pump and selected the auxiliary fuel tank for fuel supply. About 30 to 45 minutes later, with both fuel tank on/off valves in the "on" position, the engine lost power.
The pilot applied carburetor heat, but engine power was not restored. He maneuvered for a forced landing on an east-west-oriented dirt road, but determined he could not land there due to trees. He set up to land south of and parallel to the road. During descent, the left wing struck a tree approximately 20 feet above ground level. The pilot did not recall further details but stated he woke up and exited the aircraft.
Examination and Findings
An FAA airworthiness inspector examined the aircraft at the scene. The original fuel tank installed during manufacture was empty, while an aluminum fuel tank replacing the hopper tank was full. In the cockpit, yellow placards with black letters were located by the two fuel on/off valves, indicating usable fuel quantity and orientation ("push-on" and "pull-off"). No placard indicated that both valves should not be open simultaneously.
Check valves were installed at the outlets of both fuel tanks, oriented correctly for flow direction. Both check valves were removed for further examination. Testing at a military installation with FAA oversight revealed that the check valve from the original fuel tank opened at less than 1/4 psi, while the check valve from the auxiliary tank opened at 3/4 psi.
Maintenance Records and Mechanic's Statement
Review of maintenance records showed an entry dated May 25, 2003, indicating a mechanic removed all optional agricultural equipment and installed a 77-gallon aluminum fuel tank and boost pump in place of the hopper tank. The entry referenced an FAA Form 337 and stated the work was performed per the airplane type certificate data sheet, flight manual, and Advisory Circular 43.132A.
The mechanic who signed the logbook entry stated the installation was based on a previous system installed by another mechanic on his own aircraft. That earlier installation included stainless steel check valves at both fuel tank outlets, and the new owner requested similar valves. The check valves were purchased from a yacht company. As part of the installation on the accident aircraft, the mechanic stated he installed a placard by the fuel on/off valves indicating that both should not be opened at the same time. Following installation, the engine was operated with fuel supplied only from the auxiliary tank and the engine-driven fuel pump working. Static testing with fuel in the tank and the fuel line disconnected downstream of the check valve produced only a trickle of fuel. The mechanic consulted the valve supplier, who said this was normal. Further testing with pressure applied to the tank resulted in fuel flow from the disconnected line.
The mechanic also reported that the pilot asked if it was acceptable to have both on/off valves open simultaneously, and the mechanic advised against it. Before the accident flight, both the mechanic and the pilot checked the main fuel tank and noted the fuel level was down 2–3 inches, which the mechanic estimated as 4–5 gallons less than full.
FAA Inspector's Comments
According to the FAA inspector-in-charge, the installation of the 77-gallon fabricated auxiliary fuel tank was performed without FAA-approved data. Additionally, the aircraft flight manual (AFM) did not contain a supplement detailing operation of the auxiliary fuel tank system.