Diamond Aircraft Ind Inc DA 20-C1 N571MA accident near Englewood, Colorado

Probable cause

The in-flight separation of the engine throttle lever and throttle cable due to maintenance personnel not applying sufficient torque to the self-locking nut or improperly reusing a degraded self-locking nut.

NTSB analysis

While on final approach during an instructional flight, the engine became unresponsive to throttle movements. The flight instructor took control of the airplane from the student pilot and made a forced landing, during which the airplane rolled onto soft ground and nosed over to an inverted position. Engine examination revealed that the engine throttle lever and throttle cable had become disconnected and that the bolt connecting these two components was located at the bottom of the engine cowling. A self-locking nut, which normally secures this bolt, was missing and not located. Therefore, it is likely that maintenance personnel did not apply sufficient torque to the nut or improperly reused a degraded self-locking nut, which resulted in the eventual loosening of the nut and the in-flight separation of the engine throttle lever and throttle cable.

Text from the NTSB. Open the NTSB docket for CEN13LA291 for the full record.