Aircraft Accident/Incident Report

Homewood, Mississippi 39074
Tuesady, July 25, 2000 14:50 CDT

During cruise flight, a slight vibration was felt and the right propeller completely separated contacting the right horizontal stabilizer. The flight diverted and landed uneventfully. The right engine No. 3 cylinder connecting rod failed; evidence of exposure to elevated temperatures and higher stress fatigue crack propagation was noted. Extensive fretting noted on the faying surfaces of the right propeller gear and hub, and on both sides of the propeller bulkhead and fillet assembly. The holes in the propeller bulkhead assembly and propeller gear were elongated/eggshaped. Fatigue noted on all eight studs; wear noted on the shanks of seven studs; the eighth stud was not examined. Four of the recovered seven spacers were damaged shortening their length. Only two of the eight fractured studs were extended the specified minimum distance beyond the nut. No discrepancies with the threads in the hub holes of the left propeller, or to the threads in the hub holes of the right propeller that were checked. Overstress failure noted on the fractured propeller blade from the right propeller. The mechanic who installed the right propeller used un-calibrated torque wrenches and an outdated Service Manual. The airplane had accumulated approximately 50 hours since installation of the right propeller.

The inadequate installation of the right propeller by the mechanic for his failure to properly torque the eight nuts resulting in fatigue failure of the studs and separation of the right propeller during cruise flight. Findings in the investigation were 1) the mechanic who installed the right propeller used un-calibrated torque wrenches, and 2) the mechanic who installed the right propeller used an outdated Service Manual.