SALMON RIVER, ID, USA
N6159F
Air Tractor AT-802F
While conducting fire suppression operations the airplane sustained substantial damage subsequent to a loss of engine power and forced landing. The pilot reported that during a normal application run over the fire, the airplane lost engine power. Due to unsuitable terrain for an emergency landing, the pilot ditched the airplane into a nearby river. Post accident inspection of the turbine engine revealed that a compressor turbine blade was fractured in the first serration of the fir-tree root. Personnel from the Materials Laboratory examined the fracture face of the affected turbine blade and reported that the fracture surface appeared smooth with a curving boundary, typical of fatigue. Fatigue striations and ratchet marks, typical of high-cycle fatigue propagation were observed. Near the fatigue origin, no surface damage was observed, and no material anomalies were visible on the fracture surface.
On August 11, 2000, at 1136 Pacific daylight time, an Air Tractor AT-802F, N6159F, ditched in the Salmon River approximately 22 miles west of Grangeville, Idaho. The airplane is owned by Aero Spray, Inc., and was being operated as a fire suppression/aerial applicator under the provisions of Title 14, CFR Part 137. The commercial pilot, the sole occupant of the aircraft, was not injured. Visual meteorological conditions prevailed. The flight originated from Idaho County Airport, Grangeville, Idaho, approximately 20 minutes prior to the accident. In a written statement, the pilot reported that he slowed the aircraft to approximately 120 knots and made a normal application run over the fire. After completing the drop and reapplying engine power, the airplane had a "...total engine failure with fire shooting out of both exhausts". After securing the airplane's engine and jettisoning the remaining 500 gallons of fire retardant, the pilot ditched the airplane in the Salmon River. The aircraft came to rest inverted, in approximately 10 feet of water. The airplane sustained substantial damage to the fuselage and right wing. The airplane was recovered on August 16, 2000. The engine and associated engine components were removed and transported to Discount Aircraft, in Deer Park, Washington. After being inspected by representatives from the Federal Aviation Administration, Spokane, Washington, the engine was shipped to Pratt & Whitney Canada for addition teardown and inspection. During disassembly and inspection at Pratt & Whitney Canada, it was noted that a compressor turbine blade was fractured in the first serration of the fir-tree root. The remaining compressor turbine blades and compressor turbine disc were shipped to the National Transportation Safety Board, Materials Laboratory Division in Washington, D.C. for further inspection. Personnel from the Materials Laboratory examined the fracture face of the affected turbine blade and reported that the fracture surface appeared smooth with a curving boundary, typical of fatigue. Fatigue striations and ratchet marks, typical of high-cycle fatigue propagation were observed. Near the fatigue origin, no surface damage was observed, and no material anomalies were visible on the fracture surface. The blade part number was 3119171. No other markings were visible on the recovered piece of the fractured blade. According to the manufacture, a heat code is to be marked underneath the platform of each blade. The platform was missing from the fractured blade, and only blade "35" was marked with heat code number "MCG059" (Materials Laboratory Factual Report number 01-007 attached).
Compressor turbine blade failure due to high-cycle fatigue initiating in the surface of the fir-tree root. Factors include unsuitable terrain for an emergency landing.
Source: NTSB Aviation Accident Database
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