Incident Overview
A maintenance test flight of an aircraft equipped with a prototype exhaust system experienced an engine power loss and an in-flight fire during the initial climb. Smoke entered the cabin. The pilot executed a forced landing short of the runway. During the landing, the airplane touched down on soft soil, crossed a gravel driveway, and struck an embankment and a fence before coming to a stop. Subsequently, the aircraft was consumed by the fire.
Post-Accident Inspection
An Federal Aviation Administration (FAA) inspector examined the airframe and discovered an unapproved modification designed by the pilot. The modification affected the cowling and the exhaust system. The exhaust system components were wrapped with a heat-protective tape approximately 2 inches wide. After the exhaust was removed from the engine and the tape was taken off, a crack was found in the right-hand exhaust pipe collector in several areas.
Pilot's Account
The pilot reported that the experimental exhaust manifold, part of an ongoing project for a Supplemental Type Certificate (STC) aimed at drag reduction, had cracked at the weld after seven hours of test flights. The flight in question was part of the development testing of this system.