Event Overview
During cruise flight, the pilot reported a loss of manifold pressure and an inability to maintain altitude. A forced landing was initiated at Keokuk Airport, but the pilot stated he was too high and fast for a landing. A go-around was performed, yet the aircraft again approached too fast. Another go-around attempt was made, but increasing the throttle produced no additional power. The pilot then veered toward an open area to try to land, but the aircraft impacted an area of trees and fell to the ground.
Examination Findings
Post-accident examination of the aircraft revealed that the throttle arm was slipping over the serrated edges of the throttle body shaft, restricting full movement of the throttle shaft. Close-up inspection of the arm and shaft showed that the castelated nut had backed off the bolt, allowing the arm to loosen. Normally, a cotter pin is installed in the area of the castelated nut to prevent it from backing off. The bolt and nut were found still positioned on the throttle arm, but the cotter pin was not found.