On May 19, 2007, about 1816 central daylight time, a Thrush Aircraft Inc. S2RHG-T65, N40097, operated by Mettler Aerial Inc., sustained substantial damage when it impacted power lines and terrain, while maneuvering near Tyndall, South Dakota. A post impact fire occurred. The aerial application flight was operating under 14 CFR Part 137. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The commercial pilot sustained fatal injuries. The local flight departed from the Turkey Ridge Airport, near Hurley, South Dakota, at time unknown. The operator's accident report stated that "10-15 minutes before [the] crash eye witness reports indicate all was normal. Thunderstorms in the area developed rapidly. At [the] time of [the] crash eyewitness accounts, per Sheriff's report, were very heavy rain and some hail, 20 [feet] visibility." Federal Aviation Administration inspectors examined the wreckage on-scene. A section of powerline was found wrapped around the airplane's hopper. A propeller blade had a semicircular depression on its leading edge. The pilot held a commercial pilot certificate with airplane single-engine land, multi-engine land, and instrument ratings. He held a Second Class Medical certificate that was issued on March 27, 2007. On the application for that medical certificate, the pilot did not indicate taking any medications and listed "no" for "mental disorders of any sort; depression, anxiety, etc." The operator reported that the pilot's total flight time was 7,073 hours and that he had accumulated 315 hours of flight time in the same make and model as the accident airplane. N40097, was registered as a 2004 Thrush Aircraft Inc. S2RHG-T65, serial number T65HG-01, which was a tail-wheel equipped, single-engine, low-wing, all-metal airplane, used for aerial application of agricultural products. The operator reported that the last annual inspection was performed on February 6, 2007. The total time on the airframe, at the time of the inspection, was 581 hours. The airplane was powered by a Pratt &Whitney PT6A-60AG turboprop engine, serial number PCE-BG0102. At 1815, the recorded weather about 25 nautical miles and 90 degrees from the accident site at the Chan Gurney Municipal Airport, near Yankton, South Dakota, was: Wind 240 degrees at 8 knots; visibility 10 statute miles; sky condition scattered clouds 7,500 feet; temperature 28 degrees C; dew point 13 degrees C; altimeter 29.90 inches of mercury; remarks lightning observed in the distant west, thunderstorm ended at 1758. The Bon Homme County Coroner's Office arranged for an autopsy to be performed on the pilot. The FAA Civil Aerospace Medical Institute prepared a Final Forensic Toxicology Accident Report. The report stated: SERTRALINE detected in Blood SERTRALINE detected in Urine 0.048 (ug/mL, ug/g) DESMETHYLSERTRALINE detected in Blood DESMETHYLSERTRALINE present in Urine