Accident
On July 25, 2010, about 1430 central daylight time, an Air Tractor AT-602, registration N8521L, sustained substantial damage when it impacted terrain following a loss of engine power while cruising at low altitude near Yates City, Illinois. The commercial pilot received minor injuries. The airplane was registered to South Delta Aviation and operated by Har-Mor Ag Air under 14 Code of Federal Regulations Part 137 as an agricultural flight. Visual meteorological conditions prevailed, and no flight plan was filed. The airplane had departed Monmouth Municipal Airport (C66), Monmouth, Illinois, about 1255 for a local flight.
Pilot Report
The pilot reported that he flew northwest of Yates City to spray cornfields. After completing the spraying, he climbed to 500 to 600 feet above ground level to check his map for the next fields to spray. He planned to overfly those fields before refueling and loading more chemicals. He heard a loud sound, and the engine lost power. He executed a forced landing to a cornfield, requiring clearance of a power line before touchdown. The landing gear collapsed during the landing roll, causing substantial damage to the wings and fuselage. The pilot stated he had about 50 to 75 gallons of fuel remaining in the wing tanks and no chemical remaining in the chemical tank. He noted that the propeller did not go into the feathered position and that he did not manually feather it.
Aircraft Examination
A Federal Aviation Administration (FAA) airworthiness inspector examined the airplane at the accident site on July 26, 2010. The fuel tanks showed no visible fuel, though the interiors were wet with fuel. When the airplane was lifted for removal, the left fuel drain for the left wing tank was found pushed up into the wing, and fuel was observed coming out of the right wing root. The engine was removed; fuel was found in the primary fuel line to the engine, and the fuel line from the high pressure pump to the fuel/oil cooler contained about one cup of fuel. The fuel filter was full of clear fuel.
Engine Teardown
A teardown inspection of the Pratt & Whitney PT6A-60AG engine was conducted at Jet Air in Galesburg, Illinois, on August 18, 2010, with FAA oversight. The examination revealed minimal impact damage. The power section was seized due to impact deformation of the exhaust duct. The gas generator rotated freely with continuity to the accessory gearbox and all accessory drives. The power turbine control (PY) line and compressor discharge air (P3) lines showed no cracks or leaks. Upon disassembly, the compressor turbine, 1st stage power turbine vane ring, 1st stage power turbine shroud, and 1st stage power turbine exhibited light circumferential rubbing consistent with impact loads and external housing deformation.
Component Testing
The high pressure fuel pump, fuel control unit (FCU), propeller governor, and propeller overspeed governor were removed for functional testing. The high pressure fuel pump had an intact drive shaft and passed the functional test. The FCU showed a cracked housing at the throttle shaft mounting boss, consistent with impact damage; it passed the functional test with variations attributable to field adjustments and impact damage. The propeller governor had impact damage to the upper housing that precluded functional testing, but disassembly showed no preimpact anomalies. The propeller overspeed governor passed functional testing with variations attributable to field adjustments.
Fuel Information
The airplane held 216 gallons of fuel, providing about 3.2 hours endurance at high power. The operator's fuel usage form indicated that 125 gallons were added at 1255. The lineman who fueled the airplane reported the right tank was full, and the left tank was filled halfway between the 3/4 tab and the top. The flight lasted approximately one hour and thirty-five minutes.