History of Flight
On August 19, 2016, at 0807 central daylight time, a Thrush S2R-T660 agricultural airplane, registration N40499, was destroyed when it impacted a tower guy-wire and the ground during aerial spraying operations near Ruthton, Minnesota. The commercial pilot was fatally injured. The airplane was registered to and operated by Arnt Aerial Spraying, Inc., under 14 CFR Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight originated from Worthington Municipal Airport (OTG) at 0651.
The aircraft was equipped with a Satloc agricultural aerial guidance system with GPS. Downloaded flight track data indicated the airplane departed OTG and flew approximately 50 miles northwest, spraying a field about 1.5 miles west of the accident site. At 0749, it flew to the accident field and performed 16 spray passes north-south in a race-track pattern. Several passes were near a tower at the field's southwest corner; during three northbound passes, the airplane flew over the tower before descending. After the 16th pass on a northerly heading, the airplane executed a 270° right turn to a westerly heading for a perimeter pass along the northern field boundary. Following that pass, it began a left turn. The final data point at 0807:48 showed the airplane about 0.75 mile at 300° from the accident site, consistent with a turn for a south-border perimeter pass. The struck tower was about 600 ft west of the site.
Personnel Information
The 68-year-old pilot held a commercial pilot certificate with airplane single- and multi-engine land and instrument ratings, as well as a flight instructor certificate with an airplane single-engine rating. His most recent FAA second-class medical certificate, issued April 26, 2016, required corrective lenses. Review of his logbook showed no individual flight entries for 2016; the most recent entry noted "2015 spray season" and listed 16,791 hours total flight experience, matching the hours reported at his last medical examination. His most recent flight review was conducted on April 8, 2015.
Aircraft Information
The 2005-model Thrush S2R-T660, serial number T660-113, featured fixed conventional tailwheel landing gear and was designed as an agricultural spray platform. It was powered by a 1,220-horsepower Pratt & Whitney PT6A-65AG turboprop engine (serial number PCE32627) driving a five-blade constant-speed Hartzell HC-B5MP-3F propeller (serial number EVA2873). The most recent annual inspection was completed on April 12, 2016, at an airframe total time of 4,042 hours.
Meteorological Information
Weather conditions recorded at 0901 at Pipestone Municipal Airport, about 16 miles southwest, included wind from 290° at 2 knots, visibility 10 miles, scattered clouds at 2,400 ft above ground level (agl), overcast clouds at 3,400 ft agl, temperature 19°C, dew point 18°C, and an altimeter setting of 29.69 inches of mercury. According to U.S. Naval Observatory data, at 0810 the sun was 16.3° above the horizon and 88.1° east of north.
Wreckage and Impact Information
The airplane came to rest facing east in a nose-down attitude about 600 ft east of a tower estimated to be 200 ft tall. The tail section was completely separated and located near the main wreckage; flight control cables had separated with overload failure indications. The wings remained attached. The left aileron was attached; the right aileron was separated and found nearby. A portion of a tower guy-wire cable was wrapped around the right wing, starting about 3 ft from the wing root, extending along the bottom surface, wrapping around the leading edge at about 7 ft, then loosely crossing back over the trailing edge and under the fuselage. An 8-ft section of the tower with attached guy-wires was found 30 to 40 ft east of the airplane.
The propeller assembly separated and was found about 400 ft at 120° from the main wreckage. Four blades remained attached; one blade had separated and was recovered about 6 weeks later about 370 ft at 310° from the wreckage by a farmer during harvesting, having been damaged by farm equipment. Several attached blades exhibited leading-edge scratching and scoring consistent with impact during rotation. Examination revealed no preimpact mechanical anomalies.
Medical and Pathological Information
The pilot reported a history of hypertension to the FAA and was using amlodipine and benazepril, neither considered impairing. No significant abnormalities were noted during his physical examination. An autopsy by the Ramsey County Medical Examiner attributed death to multiple traumatic injuries. FAA toxicology testing was negative for all tested substances; testing for exposure to the pesticide agents lambda cyhalothrin and chloryrifos being sprayed was not possible.
Additional Information
The struck tower did not appear in the FAA Digital Obstacle File nor on the Omaha Sectional Aeronautical Chart covering the accident site. The chart depicted a windmill farm in the area with a top elevation of 2,380 ft above mean sea level (msl); the ground elevation at the accident site was about 1,900 ft msl. The tower height was estimated at about 200 ft agl, but the exact height was not determined. No airports were located within 3 miles. Title 14 CFR Part 77 requires notice to the FAA for structures exceeding 200 ft agl, and considers objects 200 ft agl or higher within 3 miles of an airport as obstructions. The tower was not subject to these requirements as its height was at or near 200 ft agl and no airport was within 3 miles.