N3748

On May 23, 2018, about 1630 Alaska daylight time, a Belite Pipper, experimental amateur built airplane, N3748, sustained substantial damage during a forced landing, following a total loss of engine power at Lake Hood Seaplane Base (PLHD), Anchorage, Alaska. The airplane was registered to a private individual and operated by the pilot as a 14 Code of Federal Regulations (CFR) Part 91 visual flight rules flight when the accident occurred. The private pilot sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed PLHD for a local flight in the airport traffic pattern.

According to the pilot, the accident flight was the first flight since maintenance was performed on the airplane's fuel system. The pilot stated that he departed Runway 32 and entered a right downwind to remain in the traffic pattern. While on final approach to Runway 32, he elected to execute a go-around. After advancing the throttle, when about 150 ft above ground level (AGL), all engine power was lost. He said the engine quit like there was no fuel. He did not see or hear anything that would be consistent with a mechanical failure.

During the forced landing, the pilot attempted to land back on the runway, but touched down between the runway end lights, bounced, and became airborne again. With no remaining runway surface available, the airplane descended into a fence and came to rest inverted in marshy terrain about 375 ft from the departure end of Runway 32. The airplane sustained substantial damage to the fuselage and both wings.

A post-accident examination of the Rotax 912 UL2 engine was performed by the NTSB investigator-in-charge along with another NTSB investigator. After removing the rocker box covers, all rocker arms exhibited discoloration consistent with high heat exposure. When the number 4 cylinder was removed, the valve was discovered fractured and a witness mark was present consistent with piston contact.

The engine had been altered from its original state by the addition of an Edge Performance Big Bore Kit. The kit, considered a high displacement cylinder/piston kit, was to increase performance and horsepower of the engine. As a result of the modification, the fuel requirements increased over that of a stock 912 UL2 engine. As installed, the kit replaced the crankshaft, camshaft, engine gaskets, cylinders and pistons. The fuel supply system remained the same and no modifications were made to the carburetors.

The pilot stated in a phone conversation that he had been discussing with the kit manufacturer a problem with fuel flow to the engine, which is why he was performing maintenance on it the day before and day of the accident. He said he had replaced all fuel lines and fittings with larger fuel lines but made no changes to the carburetors. During subsequent ground tests, fuel flow at the carburetors was measured between 1.8 – 2.0 psi.

Prior to the above-mentioned maintenance, after allowing the engine to warm up, when he would apply full power, the engine would quit and the carburetor bowls would be empty. The pilot stated that since the engine continued to run after changing the fuel lines, the "ground tests seemed good with the exception of the fuel pump pressure."