Event Description
During cruise flight, the pilot reduced the throttle to begin a descent, intending to lower manifold pressure from 24 inches to 21 inches. As the manifold pressure dropped below 21 inches, the pilot moved the throttle forward to increase power. However, the manifold pressure continued to decrease until the gauge indicated the lowest reading. The pilot then operated the throttle through its full range but received no response from the engine. A forced landing was executed to a muddy field.
Post-Accident Examination
Postaccident examination of the airplane revealed that the throttle cable had separated. The cable was examined at the NTSB Materials Laboratory, where it was determined that the cable failed as a result of fatigue cracking. The outer coiled spring housing, where fatigue was observed, had a coarse texture and contained tool marks and surface fissures. The origin of the fatigue was identified at one of the fissures. No corrosion or deposits were observed on the exterior surface of the cord.
Throttle Cable Analysis
The throttle cable had been installed new 71.3 hours prior to the accident. The fatigue cracking originated at a surface fissure that contained tool marks, indicating that the cable's failure was due to metal fatigue rather than corrosion or other environmental factors.