On August 3, 2024, about 1125 eastern daylight time, an experimental, amateur-built Glasair 3 airplane, N121CH, was substantially damaged when it was involved in an accident near Oxford, Maine. The airline transport pilot sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 test flight. The flight was the airplane’s seventh test flight in phase 1 of the amateur build. The purpose of the flight was to evaluate takeoff and landing performance. Following normal engine run-up and ground operations, the pilot departed from Oxford County Regional Airport (81B), Oxford, Maine and conducted multiple takeoffs and landings at Auburn/Lewiston Municipal Airport (LEW), Auburn, Maine and at 81B. While on downwind leg of the airport traffic pattern at 81B, the pilot noted some engine roughness after reducing power to 25 inches manifold pressure. He attempted to troubleshoot the problem with the ignition switches and the fuel selector. After returning the magnetos to the BOTH position, the engine lost all power. He then focused on performing a forced landing. After clearing some trees by extending the wing flaps, the airplane touched down on the perimeter road, collided with a fence, and came to rest in grass near the departure end of runway 33. An inspector with the Federal Aviation Administration reported that there was substantial damage to the airplane’s wings and fuselage. The landing gear separated during the forced landing. The wreckage was retained for further examination.