NTSB Factual Report

On September 21, 2012, about 1515 central daylight time, a Cessna 150G, N8465J, was substantially damaged during a forced landing following a total loss of engine power in cruise flight near Corinth, Mississippi. The certificated commercial pilot and a passenger received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight, which was conducted under the provisions of Title 14 Code of Federal Regulations Part 91.

According to the pilot/owner, the purpose of the flight was to return the airplane to his home in Oregon after he purchased it in Georgia. After receiving 2 hours of dual instruction in the airplane, the pilot and his wife departed Paulding Northwest Atlanta Airport (PUJ) and leveled the airplane in cruise flight at 4,500 feet. After approximately 2 hours of flight, with "everything perfect," a loud report came from the engine compartment, the engine cowling shook violently, and the engine experienced a total loss of power.

During the subsequent descent, the pilot attempted to restart the engine. The propeller continued to windmill, but the engine did not restart. The pilot selected a soy bean field for a forced landing, and during the landing roll, the landing gear became entangled with the crop. The airplane then nosed over and came to rest inverted, and the pilot and his wife egressed with minor injuries.

The pilot held a commercial pilot certificate with ratings for airplane single engine land and instrument airplane. He reported 960 total hours of flight experience, of which 60 hours were in the accident airplane make and model.

The airplane was manufactured in 1967, and a review of the maintenance records by a Federal Aviation Administration (FAA) maintenance inspector revealed that the most recent annual inspection was completed April 12, 2012, at 3,968 total aircraft hours. A major overhaul on the engine was completed November 12, 1986, and the engine was installed in the airplane July 22, 1988. The engine had accrued 643 total hours since that date, and 5 hours since the annual inspection.

On October 17, the engine was examined by an FAA inspector. The examination revealed that the crankshaft gear bolt locking tab washer and the alignment dowel for the gear mounting flange were fractured. The gear bolt and its associated components were examined in the NTSB Materials Laboratory in Washington, DC. The examination revealed that the locking tab and the alignment dowel displayed fracture surfaces consistent with fatigue. The bolt, the gear, and the gear mounting flange all displayed evidence of working and impact marks consistent with movement between the parts, indicative of insufficient clamping or pressure force at installation.

According to Lycoming Service Bulletin 475C, "Damage to the crankshaft gear and the counterbored recess in the rear of the crankshaft, as well as badly worn or broken gear alignment dowels are the result of improper assembly techniques or the reuse of worn or damaged parts during reassembly. Since a failure of the gear or the gear attaching parts would result in complete engine stoppage, the proper inspection and reassembly of these parts is very important."

According to Lycoming Service Instruction 1009AU, the recommended time between overhaul for the O-320 series engines was 2,000 hours. It further stated, "…all engines that do not accumulate the hourly period of time between overhauls specified in this publication are recommended to be overhauled in the twelfth year."

NTSB Probable Cause

The improper torque application on the crankshaft gear bolt by maintenance personnel during an engine overhaul, which resulted in the fatigue failure of the locking tab washer and gear alignment dowel and subsequent engine stoppage. Contributing to the accident was the operator’s exceedence of the engine overhaul calendar year limits recommended by the engine manufacturer.