Incident Overview
A pilot flying an amateur-built aircraft experienced an engine failure due to fuel starvation while approaching the destination airport. The pilot had determined the unusable fuel amount in the fuel tanks during the building process by placing the uninstalled tanks on saw horses in a level attitude, but did not account for wing dihedral, wing incidence, or pitch attitude. Departing with what he believed was an adequate fuel supply, the engine quit while the fuel selector was positioned to the right tank when the flight was 3 to 4 miles from the destination.
Sequence of Events
The pilot repositioned the fuel selector to the left tank, which restored engine power, and continued toward the airport. Approximately one minute later, the engine quit again; at that time, the fuel gauges indicated 1/8 capacity in each tank. The pilot established best glide airspeed and, after realizing he could not reach the destination airport, executed a forced landing in a marsh short of the runway. After touchdown, the airplane nosed over. The emergency locator transmitter (ELT) activated, but the wreckage was not spotted until an airplane landing at the airport flew over at 1645.
Rescue and Post-Accident Examination
During the rescue operation, the right wing was cut off, and no fuel leakage was reported. Following recovery, the left fuel tank, which was not breached, was found to contain no fuel. Additionally, only a teaspoon of fuel was found in the fuel strainer, and the carburetor bowl was dry.
Guidance on Unusable Fuel Determination
Advisory Circular (AC) 90-89A, titled "Amateur-Built Aircraft and Ultralight Flight Test Handbook" dated May 24, 1995, provides guidance for determining unusable fuel amount. The procedures call for placing the airplane at an angle 5 degrees above the highest anticipated climb angle and disconnecting the fuel line to the carburetor. When fuel flow stops, the amount remaining in the fuel tank is considered unusable.