FTW03IA073

While in cruise flight, the airplane sustained a contained in-flight right engine failure due to a fatigue failure of the propeller shaft coupling. At a cruise altitude of 9,000 feet approximately 60 miles east of his destination, the pilot heard a "bang." The engine RPM and engine temperature gauges indicated a failure of the right engine. The pilot secured the right engine, declared an emergency to air traffic control, and landed uneventfully. Examination of the propeller shaft coupling revealed a fracture that was caused by a fatigue crack that emanated from the corner radius of a lubrication slot where the corner radius converges with the root of an inner spline. At the time of the engine failure, the engine had accumulated 6,010.2 total hours since overhaul.

On August 20, 2002, approximately 0640 central daylight time, a Mitsubishi MU-2B-60 twin-engine airplane, N610CA, sustained a contained in-flight engine failure during cruise flight approximately 60 miles east of Memphis, Tennessee. The airline transport rated pilot, sole occupant of the airplane, was not injured. The airplane was registered to and operated by Bankair Inc., West Columbia, South Carolina. Visual meteorological conditions prevailed, and instrument flight rules (IFR) flight plan was filed for the Title 14 Code of Federal Regulations Part 135 on-demand cargo flight. The flight departed the William B. Hartsfield Atlanta International Airport (ATL), Atlanta, Georgia, at 0640 eastern daylight time, and was destined for the Memphis International Airport (MEM), Memphis, Tennessee.

According to the pilot, at a cruise altitude of 9,000 feet approximately 60 miles east of Memphis, he heard a "bang." The pilot reported the engine RPM and engine temperature gauges indicated a failure of the right engine. The pilot secured the right engine, declared an emergency to air traffic control, and landed uneventfully at MEM.

According to the engine logbook, on February 17, 1998, at a total engine time of 3,237.7 hours, the engine underwent a Phase 1 hot section inspection in accordance with the approved inspection program for the operator. At the time of the engine failure, the engine had accumulated 6,010.2 total hours.

An examination of the Garrett (Honeywell) TPE331-10-511M, serial number P-36192, engine by Executive Aircraft Services, Scottsdale, Arizona, revealed that the propeller shaft coupling, part number 865888-3, was fractured. The fractured coupling was sent by the National Transportation Safety Board (NTSB), Arlington, Texas, to the NTSB Materials Laboratory, Washington, D.C. for further examination.

Examination of the propeller shaft coupling by the NTSB Materials Laboratory revealed a fracture that intersected the counterclockwise corner radius of a lubrication slot (when viewed looking aft). The corner radius of the slot converged with the inner spline root radius. The fracture extended 0.4 inches in the aft direction. The coupling contained a spiral crack that was an extension of the fracture that extended from the corner radius of the lubrication slot. The crack terminated approximately 0.25 inches from the aft edge of the coupling. The scanning electron microscope (SEM) examination revealed the fracture surfaces of the crack contained crack arrest marks typical of a fatigue crack that emanated from the corner radius of the lubrication slot. Fatigue crack propagation was in the aft direction and terminated at the aft end.

The spiral crack was excised to expose the surfaces of the crack. The SEM examination revealed crack arrest marks typical of a fatigue crack. The fatigue crack propagation was in the aft direction and terminated at the external spline at the aft end.

The coupling contained another crack that also intersected the counterclockwise corner radius of a lubrication slot The crack was located two lubrication slots from the first crack. The crack extended approximately 0.5 inches in the aft direction. The fracture surfaces of the crack contained fatigue striations that emanated from the corner radius of the lubrication slot in an area where the corner radius of a post converged with the inner spline root radius. The fatigue crack propagated aft and through the entire length of the crack face.

The NTSB was notified of the in-flight failure on October 29, 2002.