Primary finding
Probable cause
The installation of a non-failsafe coupler that resulted in the separation of the throttle cable from the throttle arm and a subsequent partial loss of engine power.
Investigator assessment
Analysis narrative
During initial climb on a crosswind leg of the airport traffic pattern, the experimental amateur-built airplane exhibited a partial loss of engine power. The pilot attempted to glide the airplane to an upwind landing, but overshot the runway and landed in a field, resulting in substantial damage. Postaccident examination of the wreckage revealed that a threaded coupler between the throttle rod end and throttle cable had loosened and disconnected the cable from the throttle arm. This allowed the arm to move toward idle position. Use of a throttle cable coupler was likely a custom installation, and was not provided by the kit manufacturer. The installation provided a means to adjust the throttle cable; however, it also proved to be a single point of failure as there was no means to secure the coupler, such as a cotter pin or safety wire.
Source record
Factual narrative
On October 11, 2024, about 1647 eastern daylight time, an experimental amateur-built Glasair II SFT, N952W, was substantially damaged when it was involved in an accident near Forest, Virginia. The private pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed on a cross-country flight with 46 gallons of fuel. About 45 minutes later, upon nearing the destination airport, he entered the traffic pattern to land on runway 18. The pilot reported he had to make a left turn to avoid other inbound traffic, and he ended up circling the airport and reentering the traffic pattern on crosswind. The airplane was high during the landing approach and the pilot performed a go-around. While on the crosswind leg of the traffic pattern for a second approach, the airplane exhibited a partial loss of engine power. The pilot attempted to glide to runway 36 but overshot the runway and landed in a field. The airplane’s nose landing gear collapsed, resulting in substantial damage to the left wing and forward fuselage. Examination of the wreckage by an FAA inspector revealed that a threaded coupler between the throttle rod end and throttle cable had loosened and disconnected the cable from the throttle arm, which would allow the arm to freely move toward idle position. The inspector added that he had never seen such a coupler before on certificated aircraft. Although it provided a means to adjust the throttle cable, it also proved to be a single point of failure. Additionally, there was no means to secure the coupler, such as a cotter pin or safety wire. The inspector further stated that the airplane had accrued about 50 hours of operation since its most recent condition inspection was completed on February 1, 2024. According to the owner of the kit manufacturer, the make and model kit does not include throttle cables, and builders usually source engine controls from other companies. The owner added that he had never seen a throttle cable coupler used for aircraft. He believed it must have been a custom installation.