Cessna 172M N21391 accident near Modesto, California

Probable cause

Failure of the throttle control cable during maneuvering flight, which resulted in a partial loss of engine power.

NTSB analysis

During a photography mission, the pilot applied full engine power, and the engine speed dropped to idle. After attempting a series of troubleshooting steps, the engine did not respond, and the pilot performed a forced landing into a field. The airplane landed hard and nosed over. Postaccident examination of the engine revealed that the outer jacket of the throttle control cable had fragmented at the carburetor attach point, exposing the inner cable. Subsequent throttle control movement resulted in the cable flexing out of the jacket, rather than moving the throttle control arm at the carburetor. No life limit existed for the cable, which was most likely installed at the time of airframe manufacture, 38 years prior to the accident. Further examination of the engine revealed no additional evidence of a mechanical malfunction or failure that would have precluded normal operation.

Text from the NTSB. Open the NTSB docket for WPR13LA035 for the full record.