Cessna 172N N24CV accident near Genoa City, Wisconsin

Probable cause

A total loss of engine power due to the failure of the bolts that held in place the connecting rods to the engine's No. 3 and No. 4 cylinders as a result of the engine overhaul facility's improper installation of the bolts during a recent overhaul.

NTSB analysis

The pilot stated that during cruise flight he heard a “loud metallic clicking” sound, followed by a “bang” and a vibration. A few seconds later there was another “bang” and the propeller stopped rotating. He subsequently executed a forced landing to a corn field, where the airplane sustained damage to the firewall, nose landing gear, and wings. A postaccident examination on the engine revealed that the No. 3 and No. 4 engine connecting rod bolts had failed. Metallurgical examination determined that the bolts failed as a result of overstress fractures. No evidence of a fatigue fracture was observed. The teardown examination of the engine revealed that the nuts installed on the No. 1 and No. 2 connecting rod bolts were not tightened to the engine manufacturer’s specifications. Maintenance records indicated that the engine had been overhauled and the airplane returned to service about two weeks prior to the accident. At the time of the accident, the engine had been operated about 68 hours since the overhaul. The lack of proper torque on the intact rod bolts/nuts and the overstress failure of the remaining bolts indicates that the connecting rods were not installed properly during the overhaul procedure.

Text from the NTSB. Open the NTSB docket for CEN10LA123 for the full record.