Accident Details
On July 5, 2008, at approximately 1130 eastern daylight time, a Rockwell S-2R, registration N8499V, suffered a loss of engine power shortly after takeoff and crashed in a field near Colquitt, Georgia. The aircraft was operated by Double R Flight Service under 14 CFR Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight was originating at the time of the accident. The commercial certificated pilot sustained minor injuries, and the airplane was substantially damaged.
Pilot Statement
The pilot told an FAA inspector that before takeoff he loaded the aircraft with about 300 gallons of spray solution and topped off the left wing tank; the right tank was half full. During the initial climb at about 300 feet, he noticed a small puff of white smoke exit the exhaust, followed by a loss of engine power. At that moment, he was over a highway and decided not to jettison the chemical load due to concerns for people on the ground. The aircraft impacted the ground in a nose and right wing low attitude. The pilot reported no vibration or shudder associated with the puff of smoke and believed the engine went to flight idle without a complete loss of power.
Engine Examination
An FAA inspector examined the airplane and found the engine partially attached to the airframe and the wings substantially damaged. Examination of the Pratt & Whitney Canada PT6A-34AG engine by a manufacturer's representative with FAA oversight showed moderate impact damage but no fire damage. The compressor turbine shroud was heavily battered, gouged, and circumferentially scored. Inspection of the compressor turbine disk (P/N 301311, S/N 9963) revealed blade airfoils fractured from the root to approximately three-quarter span. The upstream side of the blade platforms displayed light circumferential rubbing across about one-third of the disk circumference from contact with the compressor turbine guide vane ring. Removal of a blade showed the part number prefix began with the letter "T." The disk was retained for further examination.
Blade Analysis
Further examination at the Safety Board's Materials Laboratory in Washington, D.C., revealed all inspected turbine blades were marked with P/N T-102401-01. The fracture surface of turbine blade No. 34 exhibited a smooth granular pattern. After blade removal, an area near the trailing edge had a green-colored appearance consistent with a preexisting crack. The fracture in the green area was located 0.15 inch above the blade platform and extended up to approximately 0.25 inch from the trailing edge. Additionally, the fracture surface exhibited areas of transgranular fracture with radial marks and curving arrest lines, features consistent with fatigue. The furthest fatigue features observed were approximately 0.32 inch from the trailing edge.
Maintenance History
Maintenance records showed the compressor turbine disk was repaired on March 24, 2005. During the repair, 58 serviceable turbine blades P/N T102401-01 were installed. These blades were FAA PMA blades manufactured by Turbo Products, Inc. The disk was approved for return to service and installed in the engine. The engine had accumulated approximately 834 hours since the repaired compressor turbine disk was installed. According to the FAA Parts Manufacturer Approval (PMA) list for Turbo Products, Inc., turbine blade P/N T-102401-01 are eligible for installation in Pratt and Whitney Canada model PT6A-11, 11AG, 15AG, 21, 25, 25A, 27, 28, 110, and 112 series engines. The list indicates that the correct P/N turbine blade for the accident engine, model PT6A-34AG, is P/N T-102401-792.