Accident Overview
On July 18, 2020, at approximately 2245 central daylight time, a Beech A23-24 airplane, registration N3412V, was substantially damaged during a forced landing near Burns Flat, Oklahoma. The pilot and three passengers were not injured. The flight was operated as a personal flight under Title 14 Code of Federal Regulations Part 91.
Sequence of Events
According to the pilot, while cruising, the airplane experienced a gradual loss of engine power. He attempted to restore power by switching fuel tanks, activating the fuel boost pump, and advancing the throttle, mixture, and propeller controls to full forward, but was unsuccessful. He executed a forced landing in a grass field. After touchdown, the airplane traversed over three large terraces. The main landing gear collapsed when the pilot attempted to swerve to avoid a tree. The horizontal stabilizer and both wings sustained substantial damage during the landing.
Investigation Findings
A Federal Aviation Administration airworthiness inspector examined the airplane at the accident site. Both wing fuel tanks contained about 25 gallons of 100 low-lead aviation fuel. The throttle control was very loose when moved by hand in the cockpit. Visual examination revealed that the throttle control rod-end was disconnected from the fuel servo throttle linkage. The retaining bolt, washer, and self-locking nut required for the connection were not found.
Maintenance History
The airplane had accumulated 8.72 flight hours since its last annual inspection, completed on October 22, 2019. The inspection authorization (IA) mechanic who performed the inspection reported that the fuel servo had been removed and overhauled in conjunction with the annual inspection. He stated that he personally reinstalled the overhauled fuel servo, while another individual moved the throttle and mixture controls in the cockpit. He noted that it was his standard practice to connect both the throttle and mixture controls to the fuel servo at the same time. He believed he likely reused the bolt and washer to connect the throttle control rod-end, and possibly reused the self-locking nut, though he would not have reused it if it had fully engaged the bolt threads by hand. He used two wrenches to secure the nut and did not use a torque wrench.
The Beech A23-24 Maintenance Manual provided no specific assembly instructions for connecting the throttle control rod-end to the fuel servo linkage. The Illustrated Parts Catalog specified that the connection requires a 169-910021 bolt, AN960-10 washer, and MS20365-1032 self-locking nut.