NTSB Identification: NYC02FA178.
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Accident occurred Monday, September 02, 2002 in Swanzey, NH
Probable Cause Approval Date: 06/02/2004
Aircraft: Beechcraft 58P, registration: N6688D
Injuries: 7 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The six-passenger airplane arrived at the departure airport with a malfunctioning landing gear system. Due to lack of maintenance personnel, the pilot elected to conduct the accident flight with the landing gear extended. The airplane departed with seven occupants, near the certified gross weight. Witnesses observed the airplane flying about 200-300 feet above the ground, with its engines "sputtering and backfiring." The airplane made a left turn towards the airport, descended, and came to rest in a wooded area about 2 miles southeast of the airport. Examination of the right engine revealed the propeller was not feathered, and the number 5 cylinder head was fractured about 3/4 inch from the bottom of the upper portion of the head. A fatigue fracture initiated in the root radius of the cylinder head thread that engaged with the top thread on the cylinder barrel. Indentations and displaced material on the upper and lower flanks of the cylinder head threads matched with the locations of protruding material observed on the cylinder barrel threads. The protruding material was located on the flank/crown radius of the threads, and was consistent with the folding over of a burr into the thread, originating during the manufacturing process. The number 5 cylinder assembly consisted of a new cylinder head that had been installed on a remanufactured barrel. The right engine was remanufactured in 2001, and had accumulated about 140 total hours of operation since. According to 14 CFR Part 91.7, "No person may operate a civil aircraft unless it is in an airworthy condition. The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur." According to 14 CFR Part 91.107, "...each person on board a U.S.-registered civil aircraft must occupy an approved seat or berth with a safety belt...during movement on the surface, takeoff, and landing." According to the Airplane Flying Handbook (FAA-H-8083-3), Transition to a Multiengine Airplanes, "When one engine fails on a multiengine airplane, performance is not halved, but is reduced by approximately 80 percent."
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's improper preflight planning, and his decision to depart with known mechanical deficiencies to the landing gear system, which resulted in a forced landing, during a partial loss of power on one engine. Factors related to the accident were the fatigue failure of an engine cylinder barrel, the inadequate manufacturing process of the cylinder barrel, the pilot's inability to retract the landing gear, and his failure to feather the propeller of the affected engine. Full narrative available
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