WPR22LA322

The pilot planned to take off and remain in the traffic pattern as part of a post-maintenance test flight of the airplane. After climbing to about 200 ft above the runway, the engine started to gradually lose power to about 15-20% engine power. The pilot had begun maneuvering the airplane for a forced landing when it entered an aerodynamic stall. The pilot attempted to recover from the stall; however, the airplane impacted terrain and nosed over, which resulted in substantial damage to the fuselage, left wing, wing struts, and empennage. Postaccident examination determined that the power supply wire for the experimental engine’s electronic control unit (ECU) was loose in the crimped terminal. It is likely that during the flight, the intermittent power source to the ECU activated the engine’s “limp mode,” which resulted in a reduction of engine power to a level that was insufficient to maintain altitude. The engine’s limp mode is a safety feature designed to protect the engine and powertrain in automotive applications.

On August 26, 2022, about 1620 mountain daylight time, an experimental, amateur-built Kitfox V Vixen, N52367, was substantially damaged when it was involved in an accident near Caldwell, Idaho. The pilot received minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he was conducting a post-maintenance test flight of the airplane after it had undergone a conditional inspection. The pilot reported that he had completed a flight down the runway in ground effect and then landed back on the runway. He then retook the runway for a flight around the traffic pattern. After climbing about 200 feet above the runway, the engine “slowly and continuously decreased power” to about 15 - 20% engine power. With no usable runway to land on, he turned to the left and attempted to land on a taxiway until he realized that a stall was imminent. He pushed the nose over and applied full right rudder and leveled the wings. The airplane impacted the ground and nosed over,sustaining substantial damage to the fuselage, left wing, wing struts, and the empennage as shown in figure 1. Figure 1. N52367, exhibiting substantial damage. Photo courtesy of the pilot. The airplane came to rest inverted in an open field on the airport. All major components remained attached to the airplane, except for the four propeller blades, which remained near the wreckage. Postaccident examination of the airframe revealed that the experimental Subaru EA-81 engine’s ECU would lose power when a wire bundle near the firewall was wiggled. The source of the intermittent power was traced to a loose wire crimped to a terminal. The wire was traced to the ignition switch 5-amp circuit breaker (figure 2). The mechanic who conducted the examination reported that the Subaru EA 81 engine had a “limp mode” feature which, when activated, resulted in a power reduction to about 25% to protect the engine and powertrain in automotive applications. An automotive mechanic, with multiple years of experience with Subaru engines, confirmed that an interruption of power to the ECU would activate the limp mode. Figure 2. Image of the electronic control module power supply wire and crimped terminal end. The wire was separated from the terminal postaccident. Photo courtesy of the Federal Aviation Administration.