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On August 4, 2010, about 1130 eastern daylight time, an Ayres Corporation S2R-T34, N4004D, was substantially damaged when it impacted trees and terrain during a forced landing, following a loss of engine power near Donalsonville, Georgia. The certificated commercial pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which originated from Donalsonville Municipal Airport (17J), Donalsonville, Georgia. The aerial application flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 137.
During a telephone interview, the pilot recounted the events that transpired just prior to, and during the accident flight. Prior to departing, the airplane's fuel tanks were filled, and 300 gallons of chemicals were loaded. The purpose of the flight was to apply the chemical to a peanut field, located about 5 miles northeast of 17J. After applying chemical to the interior of the field, the pilot maneuvered the airplane and began spraying the outer portions of the field. While transitioning the airplane to the final segment of the application, at an altitude between 200 and 300 feet above ground level, the engine "quit." The pilot further described that he heard a "pop" sound, heard the engine "spool down," and observed blue smoke trailing from the top of the engine cowling. All of the engine instruments appeared to be indicating normally prior to the loss of power.
The pilot selected a nearby field and maneuvered the airplane for the forced landing. Since time during the descent was limited, the pilot did not attempt to shut down or secure the engine. The airplane touched down in a cow pasture and struck a fence row before coming to rest. The pilot then noted the sound of "something spinning" coming from the engine cowling before he subsequently shut down the engine, after which the sound ceased. Upon exiting the airplane, the pilot saw oil draining from the lower aft portion of the engine cowling.
A review of Federal Aviation Administration (FAA) airman records revealed that the pilot held a commercial pilot certificate with a rating for airplane single-engine land. The pilot's most recent second-class medical certificate was issued in January, 2010.
The accident airplane was a single-seat aerial application aircraft, manufactured in 1978. It was equipped with a single Pratt and Whitney Canada PT6A-34AG turbo-propeller engine. A 100-hour inspection of the engine was completed on May 6, 2010, and at that time the engine had accumulated 13,112 total hours of operation, and 1,036 hours since the most recent hot section inspection. The most recent hot section inspection was completed on August 24, 2007 at an engine total time of 12,076 hours. During that inspection it was noted that the compressor turbine disc tip clearance was 0.014 inches. The hot section was previously inspected on May 2, 2000, at 7,918 engine hours, and the compressor turbine was repaired at that time. Further details of the repair were cited in a work order that was not recovered. Based on the records provided, the installation date and the total accumulated operational hours of the compressor turbine blades could not be determined. Additionally, no entries detailed if an overhaul inspection of the compressor turbine blades had been completed.
WRECKAGE AND IMPACT INFORMATION
A FAA inspector examined the wreckage at the scene, and noted that the propeller was "locked" and not free to rotate. The airframe and engine were recovered from the site to a maintenance facility, where the engine was examined in detail by the FAA inspector and a representative of the engine manufacturer.
The engine remained attached to the airframe, and the propeller, reduction gearbox, and mounted controls and accessories were in place and intact. The exhaust duct displayed light compression deformation and external pockmarks and dimples adjacent to the left side exhaust port flange. The gas generator rotor was free to rotate with slight resistance, while the power section was seized. The combustion chamber liner displayed no indications of distress.
The compressor turbine guide vane right trailing edges and compressor turbine shroud were battered and gouged consistent with separated turbine blade debris contact, and displayed melted compressor turbine blade material across the shroud surface. The compressor turbine blades were fractured at about 1/3 to 1/2 of their respective spans, and displayed burning, erosion, and coating loss. Visual and macroscopic inspection of the blade fracture surfaces displayed no indications of fatigue or other progressive fracture mechanism. The power turbine guide vane airfoils were battered and gouged consistent with contact with separated compressor and power turbine blades. Melted compressor turbine blade material was distributed across the vane airfoils.
The compressor turbine blades were manufactured by Doncasters Turbo Products and displayed a part number of T-102401-100. According to maintenance and inspection documentation published by the manufacturer, the blades were FAA Parts Manufacturer Approval-type replacements for Pratt and Whitney Canada compressor turbine blade part number 302401-100. The blade manufacturer required that the compressor turbine blades be submitted for overhaul inspection after the first 5,000 hours in service and every 3,000 hours thereafter. The blade manufacturer also noted that when measuring the blade tip clearance, it should fall within a range between 0.010 and 0.017 inches.