FTW00LA178

The pilot was returning the agricultural airplane to the airport to pick up a second spray load when he heard a 'deep humming sound coming from the engine.' The pilot added that white smoke was emanating from the engine's exhaust, and that the propeller feathered and came to a stop. The pilot landed the airplane in a flooded rice field. The main landing gear dug into the mud resulting in the airplane nosing over. Post-accident examination of the Pratt & Whitney PT6A-15AG engine revealed that one of the teeth on the reduction gearbox's 1st stage sungear failed as a result of fatigue. The fatigue fracture originated from an area of pronounced wear. Numerous gear teeth displayed wear and spalling damage. The gear was found to be within the manufacturer's hardness and dimensional limits. The engine had exceeded the manufacturer's recommended 3,500-hour overhaul period by 4,153 hours.

On June 6, 2000, at 1440 central daylight time, a Gulfstream-Schweizer G-164D agricultural airplane, N8337K, was substantially damaged during a forced landing following a loss of engine power near Welsh, Louisiana. The commercial pilot, who was the sole occupant, received minor injuries. The airplane was registered to and operated by Lyon Flying Service, Inc., of Welsh, Louisiana. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 137 aerial application flight. The local flight originated at 1400, from the Welsh Airport.

According to the operator, the pilot completed the first of two spray runs, and was returning to the airport to fill up for the second run when he heard a "deep humming sound coming from the engine." The pilot saw white smoke coming from the engine exhaust. Subsequently, the propeller feathered and came to a stop while the airplane was at 300 feet agl. The pilot landed the airplane in a flooded rice field. During the landing roll, the main landing gear sank into the mud, and the airplane nosed over and came to rest inverted.

According to the operator, the Pratt & Whitney PT6A-15AG engine had seized preventing the compressor section from rotating. The FAA inspector, who visited the accident site, stated that the fuselage, wings, and empennage sustained structural damage.

The engine was transported to the Pratt & Whitney facility located in Longueuil, Quebec, Canada. The engine was examined on July 19, 2000, under the supervision of a technical investigator from the Transportation Safety Board of Canada. According to the Pratt & Whitney Accident/Incident Report, the "engine lost useful power due to the fatigue fracture of [the reduction gearbox's] 1st stage sungear tooth [which unloaded] the power turbine rotor, allowing the power turbine to accelerate to an overspeed condition and release the power turbine blades." According to the Pratt & Whitney Materials Investigation Laboratory Report, the 1st stage sungear's fatigue fracture originated at the "root radius run out of one of the teeth in area of pronounced wear." Additionally, most of the remaining teeth displayed "wear and spalling damage." The 1st stage sungear's hardness and dimensional values were within the manufacturer's specifications.

According to the engine maintenance records, the engine had accumulated a total of 7,653.10 hours, and had accumulated 234.0 hours since its last hot section inspection. There was no record of an overhaul being performed. Pratt & Whitney's Accident/Incident Report also mentioned that the engine had been operated approximately 4,153 hours in excess of their recommended time between overhauls of 3,500 hours.