LAX95LA345

Shortly after takeoff, the engine lost power and the pilot made a forced landing near the airport. The pilot said that he had built the experimental airplane, and had installed the engine and its accessories. Engine examination revealed that the left-hand carburetor slide valve was improperly installed and was leaking. The right-hand carburetor choke was partially open and the vent lines were improperly routed. The engine integrity and ignition system operated normally. According to the engine manufacturer, the carburetor anomalies and the improperly routed vent lines would result in an engine loss of power.

On September 29, 1995, at 1747 hours Pacific daylight time, an experimental Pro-Built Aviation, Inc., Kitfox IV Speedster, N42RA, crashed after experiencing a loss of engine power shortly after departing runway 28 at Lampson Airport, Lakeport, California. The pilot was beginning a local visual flight rules personal flight. The airplane, registered to Pro-Built Aviation, Inc., Martinez, California, sustained substantial damage. The certificated private pilot and passenger received minor injuries. Visual meteorological conditions prevailed.

The pilot told National Transportation Safety Board investigators in a telephone interview conducted on September 29, 1995, that the engine began to run rough shortly after reaching 300 feet above the ground. The pilot applied the fuel boost pump to alleviate the roughness, but without success.

When it became evident that a forced landing was inevitable, the pilot elected to land in an open area. As he approached the open area, the pilot realized that the airplane's altitude was insufficient to clear a corral and high tension wires. He then intentionally stalled the airplane about 8 feet above the ground to avoid hitting the obstacles and landed in an 80-foot-long open area.

On December 8, 1995, an FAA airworthiness inspector from the Sacramento [California] Flight Standards District Office, a representative from A.C. Ultra Aviation (the engine manufacturer), and an independent fixed-base operator disassembled the engine for examination.

According to the FAA inspector, the engine was intact and sustained minor impact damage. He said that he found unidentified material near the flywheel and the magnets. The distributor coil was free of the material.

Investigators established continuity of the engine gear and valve train assembly.

The left carburetor throttle slide valve was found installed 90 degrees off its proper position; the right throttle slide valve was installed according to the manufacturer's maintenance manual. Fuel stains were found on the left carburetor valve.

The right carburetor choke arm nut was missing and the choke was partially open. The carburetor vent lines were extended and did not comply with the manufacturer's installation recommendations. The ignition system produced sparks when the engine was rotated with the starter.

The manufacturer's representative said that the left-hand carburetor slide valve and right carburetor activated choke would result in "excessive vibration, engine stumbling, and possible stoppage." He also said that "the incorrectly routed fuel vent lines would create a differential pressure between the carburetor intakes and float bowl chambers, which also would create unstable fuel delivery, rough running, excessive vibration, and possible stoppage."