On August 23, 2011, at 1853 central daylight time, an Air Tractor AT-400, N23720, was substantially damaged when it collided with trees and terrain near Monango, North Dakota. The pilot sustained serious injuries. The airplane was registered to and operated by D-Lux Spray Service, LLC, under the provisions of 14 Code of Federal Regulations Part 137. Day visual meteorological conditions prevailed for the flight, which was operated without a flight plan. The aerial-application flight departed Edgeley Municipal Airport (51D) at approximately 1819.

The pilot reported that he remembered completing a majority of his spray runs and was finishing along the field's edge when the accident occurred; however, he had no recollection of the airplane colliding with the trees or terrain.

A postaccident examination conducted by Federal Aviation Administration inspectors established that the airplane's right wingtip contacted a cottonwood tree before the airplane collided with terrain. There was a wreckage debris path, about 100 yards long, preceding the main wreckage which was located in a roadside ditch. The debris path contained fragmented portions of the airframe, wings, and tree branches. The fuselage and wings were substantially damaged during the accident sequence. There was no evidence of a postimpact fire. The east/west power transmission line, situated along the north side of the roadway, appeared undamaged.

The postaccident examination did not reveal any mechanical malfunctions or failures that would have precluded normal operation of the airplane. The engine fuel control unit (FCU), fuel filter bowl, flow divider, and fuel lines contained fuel. The splined driveshaft connecting the fuel pump to the accessory gearbox was sheared and exhibited rotational damage. The nylon coupler between the fuel pump and the FCU exhibited fracture features consistent with torsion overload. The engine compressor section, FCU flyweights, and propeller exhibited rotational damage consistent with a sudden stoppage event.

A handheld global positioning system (GPS) receiver was found at the accident site. The position data downloaded from the GPS device showed the airplane departing 51D approximately 34 minutes before the accident. After departure, the airplane flew about 16 miles southeast to the field contracted to be sprayed. The plotted data was consistent with aerial application maneuvers being performed during the remainder of the accident flight. The last 15 seconds of GPS data showed the airplane on west-northwest heading descending from approximately 300 feet above ground level (agl) to less than 100 feet agl. The final two data points were located amongst a sparsely wooded area when plotted on an aerial-survey image.

At 1855, the automated surface observing system at the Gwinner-Roger Melroe Field Airport, located about 41 miles east of the accident site, reported the following weather conditions: wind 210 degrees at 9 knots; visibility 10 miles; clear skies; temperature 30 degrees Celsius; dew point 25 degrees Celsius; altimeter setting 29.61 inches of mercury.

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