NTSB Factual Report

On July 5, 2008, about 1130 eastern daylight time, a Rockwell S-2R, N8499V, experienced a loss of engine power shortly after takeoff and crashed in a field near Colquitt, Georgia. The commercial certificated pilot received minor injuries and the airplane was substantially damaged. The airplane was operated by Double R Flight Service under the provisions of Title 14 Code of Federal Regulations (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 pilot stated to the responding Federal Aviation Administration (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 time, he was over a highway and decided not to jettison his chemical load due to concerns for the safety of people on the ground. The aircraft impacted the ground moments later in a nose and right wing low attitude. The pilot further reported that there was no vibration or shudder associated with the puff of smoke, and he believed the engine went to flight idle and never completely lost power.

Examination of the airplane by an FAA inspector revealed that the engine remained partially attached to the airframe, and the wings were substantially damaged.

Examination of the Pratt & Whitney Canada PT6A-34AG engine by a representative of the engine manufacturer with FAA oversight revealed the engine displayed moderate impact damage but no fire damage. The compressor turbine shroud was heavily battered, gouged, and circumferentially scored. Inspection of the compressor turbine disk part number (P/N) 301311, serial number (S/N 9963, revealed the blade airfoils were fractured from the root to approximately three quarter span. The upstream side of the blade platforms displayed light circumferential rubbing across approximately one third of the disk circumference due to contact with the compressor turbine guide vane ring. Removal of one of the blades revealed the P/N prefix began with the letter “T.” The disk was retained for further examination.

Examination of the compressor turbine disk was performed at the Safety Board’s Materials Laboratory located in Washington, D.C. The results of the examination revealed all inspected turbine blade were marked with P/N T-102401-01. The fracture surface of turbine blade No. 34 exhibited smooth granular pattern. Following removal of the blade from the disk, an area near the trailing edge had a green colored appearance which is consistent with a preexisting crack. The fracture in the green colored 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 that are consistent with fatigue. The furthest fatigue features observed was approximately 0.32 inch from the trailing edge.

Review of the maintenance records revealed the compressor turbine disk was repaired on March 24, 2005. During the repair 58 serviceable turbine blades P/N T102401-01 were installed. The turbine 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 to be installed 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.

NTSB Probable Cause

Loss of engine power due to the installation of incorrect turbine blades on the compressor turbine disk during repair of the disk assembly.