NTSB Factual Report

On May 24, 2002, at 1130 central daylight time, an Ayres S2R-T34 Thrush single-engine agricultural airplane, N4025Y, was substantially damaged during a forced landing following a loss of engine power during the initial takeoff climb from a private grass airstrip near Aubrey, Arkansas. The airplane was registered to and operated by Riddell Flying Service Inc., of West Helena, Arkansas. The commercial pilot, sole occupant of the airplane, was not injured. 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 was originating from the Old Gibson Airstrip in Aubrey at the time of the accident.

According to the pilot, he had flown approximately 16 spray runs prior to the accident and did not experience any anomalies with the airplane. The airplane departed for the 17th spray run with 200 gallons of fuel and 2,500 pounds of Urea, a fertilizer, on board. The airplane was climbing through 100 feet when he heard a "loud bang," and the engine lost total power. The loss of engine power was accompanied by smoke, which was emanating from the engine exhaust. The pilot noted that the oil pressure and fuel pressure gauge needles had dropped to zero. Subsequently, the pilot executed a forced landing to a field, during which both main landing gear assemblies separated from the airplane, and the right wing's spar was damaged.

The airplane was powered by a Pratt & Whitney PT6A-34AG turboprop engine (serial number 56924) that had accumulated a total of 14,598 hours since new. On December 10, 1994, the compressor turbine blades were installed, at which time the engine had accumulated a total of 9,849 hours. On November 7, 2000, a hot section inspection was completed. On May 9, 2002, the engine's most recent inspection, a 100-hour inspection, was completed. A complete engine overhaul had never been performed. According to Pratt & Whitney Service Bulletin No. 1303, the recommended overhaul interval for the engine is 3,500 hours.

The engine was examined at the Pratt & Whitney Facility in Montreal, Canada, under supervision of the Transportation Safety Board of Canada. The 1st stage compressor blades, shroud and stator displayed no indications of foreign object damage or other distress. The combustion chamber was intact and the flame pattern was consistent with normal operation. The compressor turbine guide vane ring's trailing edge and the compressor turbine shroud both displayed gouges and pockmarks consistent with contact from separated compressor turbine blade debris. The compressor turbine blades were all fractured at varying heights between 1/4 and 1/2 span. Macroscopic inspection of the blade fracture surfaces revealed signatures typical of overload, with collateral mechanical damage. Material analysis of the compressor blades, conducted by Pratt & Whitney, revealed no indications of fatigue or material creep. The blades material composition was in accordance with the manufacturer's specifications. The power turbine guide vane airfoil leading edges displayed nicks and gouge marks consistent with contact from separated compressor turbine blade debris. Approximately 3/4 of the power turbine blades were fractured at varying heights, and displayed characteristics of contact with separated compressor turbine blades debris and contact with the power turbine shroud.

NTSB Probable Cause

The failure of a compressor turbine blade(s) for an undetermined reason.