Cessna 172S N60372 accident near Casa Grande, Arizona

Probable cause

An in-flight separation of the throttle linkage, which resulted in a loss of throttle control. Contributing to the accident was maintenance personnel’s failure to follow the maintenance manual inspection procedure for the throttle cable assembly.

NTSB analysis

The pilot and safety pilot departed to practice simulated instrument approaches at a local airport. As they approached the airport, they observed that the throttle was in the full open position but the tachometer indicated 1,900 rpm. The safety pilot, a certificated flight instructor, took control of the airplane and attempted to cycle the throttle but was unsuccessful in his attempt to restore engine power. The engine speed remained at 1,900 rpm for the remainder of the flight regardless of the throttle position. During the emergency landing at the airport, the airplane touched down at a high rate of speed. The safety pilot reduced the mixture control to idle/cutoff and landed in a field at the end of the runway. The airplane impacted a tree, which resulted in substantial damage to the left wing.

Postaccident examination of the airplane revealed that the throttle linkage had separated from the throttle arm. The threads on both the linkage and threaded section of the arm were intact and both jamnuts were loosely threaded to the linkage. The absence of any damage to the throttle assembly suggests that the linkage likely unthreaded itself from the throttle arm during the accident flight, which resulted in a loss of throttle control.

The separation likely developed over the course of the airplane’s 680 flight hours since the throttle linkage was installed and should have been discovered during one of the subsequent required 50-hour inspection intervals or the airplane’s most recent 100-hour inspection. However, none of these inspections were accomplished in the 680 hours of operation.

Text from the NTSB. Open the NTSB docket for WPR23LA199 for the full record.