Cessna 172 N6486J accident near Melba, Idaho

Probable cause

The total loss of engine power due to a separated carburetor idle mixture adjustment screw and spring assembly for reasons that could not be determined.

NTSB analysis

The flight instructor and student pilot were performing maneuvers when the engine lost total power. The instructor pitched the nose of the airplane down and asked the student pilot to restart the engine. The student pilot was unable to rotate the engine using the starter, and the flight instructor verified that the master switch was in the “ON” position. The instructor tried to start the engine himself and was unsuccessful. The flight instructor performed a forced landing in a field.

Examination revealed that the idle mixture adjustment screw and spring assembly had separated from the carburetor and were found in the lower cowling area. After the airplane was relocated to a nearby road the engine rotated via the starter.

Examination of the idle mixture adjustment screw and spring assembly revealed no anomalies. The reason that the screw backed out of the carburetor could not be determined. The starter solenoid was removed and disassembled. The starter solenoid was examined and revealed a frayed and separated wire from the coil to a terminal end. The reasons for this fraying and separation could not be determined. Although the starter solenoid was faulty, it is unlikely that the engine would have restarted due to the separated idle mixture screw and spring assembly.

Text from the NTSB. Open the NTSB docket for WPR19LA092 for the full record.