On July 13, 2007, at 2045 eastern daylight time, an experimental Sopwith F1, N6338, experienced a loss of engine power and collided with terrain during a go-around at Greenville Municipal Airport, Greenville, Pennsylvania. The pilot, who was the owner and builder, was operating the airplane under the provisions of 14 CFR Part 91. The private pilot, the sole occupant, sustained serious injuries. The airplane sustained substantial damage. The local area personal flight departed Greenville about 2000. Visual meteorological conditions prevailed; no flight plan had been filed.

In a telephone interview with a National Transportation Safety Board investigator, the pilot stated that on the day of the accident the airplane fuel tanks were approximately 1/4 full. He departed Greenville for a pleasure flight, and on returning to the airport attempted a landing. During the approach he elected to perform a go-around. He applied full power, but the engine did not respond; he pumped the manual fuel pressure handle a few times and the engine regained power for approximately 10 seconds, but then lost all power. The airplane collided with terrain in a corn field.

The pilot stated that both an engine driven pump and a fuel tank air pressurization system maintain fuel pressure for the Gnome 9N engine. A small propeller driven air pump, mounted on the right wing strut, maintains air pressure in the tank. A pressure relief valve is integrated into the propeller-pump, and is set to maintain a system pressure of 1.5 psi. During ground operations, a pilot operated hand pump maintains pressure.

The pilot stated that during previous flights he was concerned that the fuel system may not be able to provide enough fuel pressure to supply the engine. He performed flight tests in various phases, including go-around, and at various flight attitudes. He reported being able to achieve dependable engine performance. He noted that during these tests the fuel tank was full prior to flight.

The pilot surmised, that on the day of the accident, the 1/4 tank of fuel onboard did not provide the head pressure that existed on previous flights. He also stated that the pressure relief valve should be adjusted so that greater pressure can be maintained in the fuel system. He stated that he designed the fuel system to replicate the original Sopwith F1 Airplane, using limited historical documentation.

According to Federal Aviation Administration Advisory Circular AC 20-27F, Certification and Operation of Amateur-Built Aircraft, "Amateur builders are free to develop their own designs or build from existing designs. We do not approve these designs and it would be impractical to develop design standards for the wide variety of design configurations, created by designers, kit manufacturers, and amateur builders."

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