Incident Overview
During the initial climb following takeoff, the airplane's engine lost power. The aircraft was at approximately 400 feet above ground level while turning onto the left crosswind leg of the airport traffic pattern when the engine lost power completely. The pilot executed a forced landing between a taxiway and the perimeter fence on the airport, resulting in damage to the airplane.
Preflight and Initial Climb
The run-up check conducted before departure was uneventful, with no anomalies noted. Shortly after takeoff, however, the engine failed, leading to the forced landing.
Post-Accident Examination
A post-accident test run of the engine revealed a critical issue with the mixture control cable. The cable was found to be fractured 0.35 inches from the set screw that attaches it to the carburetor. The fracture was hidden by the outer sheath covering the cable. As a result, movement of the mixture control in the cockpit did not produce corresponding movement of the carburetor mixture arm, which was free to move uncommanded.
Fracture Analysis
When the fracture surfaces were realigned, the wire appeared to have been bent nearly 90 degrees from its normally straight path. Scanning electron microscopy (SEM) of both fracture surfaces showed a fatigue crack covering approximately one-quarter of the wire's cross-sectional area, oriented perpendicular to the wire's surface. The origin of the fatigue crack was on the outside surface of the 90-degree bend, suggesting that the crack initiated and propagated during service while the main portion of the wire was under compression loads.
Probable Cause
The presence of the fatigue crack is indicative of an installation problem, such as overtorquing of the set screw. The fracture of the mixture control cable prevented the pilot from properly setting the mixture from the cockpit control to the carburetor, leading to the loss of engine power.