Cessna 172R N77AF incident near West Chicago, Illinois

Probable cause

A partial loss of engine power due to the detachment of the throttle control cable from the throttle assembly during a landing approach. Contributing to the accident was the lack of a redundant means to preclude the detachment of the cable from the throttle assembly.

NTSB analysis

A previous maintenance entry in the airplane logbook indicated that the firewall was replaced and the airplane returned to service. The airplane had been operated for about 63 hours when the throttle control cable became unscrewed from the rod end of the throttle assembly during an instructional flight. The flight instructor and student pilot lost throttle control during an approach to a destination airport when engine speed increased to about 2,200-2,300 rpm. The flight instructor landed the airplane without further incident. The throttle control assemblies for the airplane do not have a key way at the throttle control knob to prevent rotation of the cable and unscrewing of the cable from the rod end should the jamnut become loose. The operator recommended that a safety device and not just a jamnut be installed to prevent the throttle control from disconnecting from the rod end.

Text from the NTSB. Open the NTSB docket for CEN09IA456 for the full record.