N1515PAir Tractor AT-502 · 1991

On June 21, 2011, about 1621 mountain daylight time, an Air Tractor AT-502, N1515P, sustained substantial damage when it impacted trees during takeoff from the McCarley Field Airport, Blackfoot, Idaho, following a reported partial loss of engine power. The airplane was registered to Wells Fargo Bank Northwest, Salt Lake City, Utah, and operated by Vector Disease Control International, Little Rock, Arkansas, under the provisions of Title 14 Code of Federal Regulations Part 137. The commercial pilot, sole occupant of the airplane, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the local aerial application flight that was originating at the time of the accident.

The pilot reported to the National Transportation Safety Board investigator-in-charge (IIC) that he had been flying throughout the day conducting local aerial application flights uneventfully with about 320 to 375 gallons of chemicals loaded in the hopper. Prior to takeoff on the accident flight, he conducted his pre takeoff checklist by setting the propeller, power lever, flaps, and verifying all engine gauges and flight controls. The pilot stated that during the takeoff roll on runway 1, the airplane became airborne slightly beyond the normal rotation point and that as the airplane approached the departure end of the runway, the engine failed to develop enough power to maintain flight. The pilot stated that he focused on flying the airplane and did not look at the engine gauges and that due to the amount of runway remaining; he was unable to abort the takeoff. The pilot said that he lowered the nose in an effort to gain more airspeed and did not jettison the chemical load in the hopper.

The pilot reported that at the time of the accident, the airplane weighed approximately 6,914 pounds, which included the 320-gallons of chemicals in the hopper and three-quarters of a tank of fuel in the left and right wing tanks. The maximum gross weight of the airplane was 8,000 pounds.

Examination of the airplane by local law enforcement revealed that the outboard six feet of the right wing was separated and the outboard three feet of the left wing was separated. Fuel was accounted for in both wing fuel tanks at the accident site. The wreckage was recovered to a secure location for further examination.

Examination of the recovered turbine engine by a representative from Pratt & Whitney Canada, under the supervision of a Federal Aviation Administration (FAA) inspector revealed that the engine displayed circumferential contact signatures to the compressor turbine, the power turbine guide vane ring, the power turbine shroud, the power turbine, and impact fractures of the power turbine blades due to their making contact with their adjacent components under impact loads and external housing deformation. There were no indications of any pre-impact distress or operational dysfunction to any of the engine components examined. The representative from Pratt & Whitney Canada noted within his report that the engine displayed contact signatures to its internal components characteristic of the engine developing power at the time of impact, likely in a high power range.

The company representative responsible for loading the chemical mixture onto the airplane reported that prior to the accident flight the airplane was loaded with 304 gallons of water, 12 gallons of Ethephon, 1.81 gallons of Shar-Sheild, and 1.81 gallons of Quadris. The company representative further stated that this was the pilot's usual load and all amounts loaded onto the airplane were verified by the pilot.

Review of recorded weather data at the Pocatello Regional Airport, located about 20 miles southwest of the accident site revealed at 1553, wind was from 270 degrees at 9 knots. The pilot reported that at the time of the accident, wind was from 250 degrees between 0 and 3 miles per hour. Using reported weather conditions, airport elevation, the approximate density altitude was calculated to be about 6,650 feet.