ATL96LA131

During cruise flight, about half of one propeller blade separated from the airplane, resulting in substantial damage. An uneventful landing was made to a nearby airport. Metallurgical examination of the propeller blade revealed that it had failed from fatigue; the fatigue originated from a single corrosion pit on the camber side of the blade. Other corrosion pits were also noted on the camber side of the remaining portion of the blade. There was no record in the airplane log that the propeller had been reconditioned since its installation. The propeller was manufactured in September 1963 and sold to Beech Aircraft Corporation in August 1964. The airplane was manufactured in December 1964 and had accumulated 1851 hours of flight time. The propeller manufacturer recommended that the propeller be reconditioned after each 1,000 hours of operation.

On September 20, 1996, about 1200 eastern daylight time, a Beech A-23, N8879M, experienced the separation of about one half of one propeller blade during cruise flight, near Tarboro, North Carolina. The airplane was operated by the pilot/co-owner under the provisions of Title 14 CFR Part 91, and visual flight rules. Visual meteorological conditions prevailed. A flight plan was not filed for the business flight. There were no injuries to the commercial pilot or the pilot rated passenger, and the airplane was substantially damaged. Origination of the flight was Lake Ridge, North Carolina, about 1130 on the same day. The flight was destined for Williamston, North Carolina.

According to the pilot, while in cruise flight about 3,500 feet mean sea level, one propeller blade separated from the airplane. At the time, the airplane was about one half mile southeast of the Tarboro-Edgecombe County Airport. The pilot turned the airplane toward the airport and landed uneventfully.

The propeller had separated through one airfoil on a chordwise plane about 14.5 inches outboard of the propeller centerline. During a metallurgical examination of the remaining fracture surface, fracture features typical of fatigue progression from a single origin were observed. A corrosion pit was observed at the origin, located on the camber surface of the blade, about 2.75 inches aft of the leading edge. The camber surface was not painted and several other corrosion pits were visible in the surface. A longitudinal pattern of scratches consistent with hand polishing was visible on the camber surface from the fracture inboard to the edge of the hub area. The flat surface of the propeller was painted black.

According to the Federal Aviation Administration (FAA) airworthiness inspector who participated in the investigation, the failed propeller, a Sensenich M74DC-O-60, serial number B920, was manufactured on September 23, 1963, and sold to Beech Aircraft Corporation on August 17, 1964. The airplane logs indicated that the airplane was initially issued an Airworthiness Certificate on December 11, 1964. The airplane log did not reflect the propeller serial number. The airplane log contained the following entries regarding the propeller: * 10/13/95 installed new spinner, backing plate, and front plate; total hours-1820.1 * 12/24/79 dressed and painted propeller; annual inspection; total hours-1111.15 * 09/08/76 dressed nicks in propeller and painted blades. Retorqued propeller and repaired spinner backplate; total hours-795.88

There was no indication in the aircraft logs that the propeller had been replaced or reconditioned, since its original installation. The FAA inspector stated that ,after the accident, the hour meter on the airplane indicated 1851.21 hours. Propeller specifications provided by the propeller manufacturer indicated that the recommended time between reconditioning of the propeller was 1,000 hours.