HISTORY OF FLIGHT On November 30, 2014, about 0115 mountain standard time, a single-engine Air Tractor, Inc. AT-502B, N946TR, impacted an open field near Somerton, Arizona. Tri Rotor Spray and Chemical, Inc., operated the airplane under the provisions of 14 Code of Federal Regulations Part 137 as a local aerial application flight. The pilot, the sole occupant, was fatally injured; the airplane was destroyed in the postcrash fire. The airplane had departed from a private airstrip about 0110. Visual night meteorological conditions prevailed for the flight, and a company flight plan had been filed. According to a company representative, prior to the accident the pilot had landed the airplane, and placed 100 gallons of water onboard. The intent was to do a water calibration flight to end his day. After the field had been sprayed with water, the pilot was returning to land. The company representative reported that no radio communications were made prior to the accident between the pilot and other company pilots flying in the area. A company pilot saw a flash as he was taking off. He flew toward the direction of the flash, and saw an airplane engulfed in flames. The pilot landed his airplane near the accident site, but stated that he was not able to get close due to the flames. There were six pilots in the area at the time of the accident. They all reported small areas of patchy fog conditions. Their estimation based on their specific location was that the patchy fog layer was between 150-400 feet above ground level with good visibility. PERSONNEL INFORMATION The pilot, age 55, held a commercial pilot certificate with ratings for airplane single- and multi-engine land, and instrument airplane; he also held a helicopter rating. The pilot held a second-class medical certificate issued on September 23, 2014, with the restriction that he must wear corrective lenses. The pilot reported 12,200 total hours with 45 hours in the past 6 months on his medical certificate application. The date of his last flight review was March 18, 2014. According to the operator, the pilot's last flight review was performed on March 18, 2014, in a Bell 206B. AIRCRAFT INFORMATION The single-engine low-wing conventional-geared Air Tractor AT-502B airplane, serial number 502B-2946, was equipped with a Pratt and Whitney PT6A-34AG turbo-prop engine. According to the operator, a 100-hour inspection was performed on November 2, 2014. The airframe total time was 502.2 hours. The engine had a total of 20 hours since the last inspection. METEOROLOGICAL INFORMATION A weather study was performed by a senior meteorologist from the NTSB; the report is attached to the public docket for this accident. In part, it was reported that a moist layer existed in the low farming region where the accident occurred. The temperature was 50.7 degrees F, dew point was 48 degrees F and relative humidity was 91 percent. The existing fog layer was not extensive nor was it observed at Yuma, Arizona, or indicated on satellite imagery. Aircraft soundings for the area indicated strong surface based temperature inversion with light winds, which was below favorable for light fog or mist formation. There were no National Weather Service weather advisories in effect for extensive instrument flight rules conditions, low-level windshear, or turbulence across the region at the time of the accident. WRECKAGE AND IMPACT INFORMATION The accident site was situated at the intersection of County 18-3/4's street and Avenue E South in an open field, with no obstacles identified in the flight area. The entire airplane came to rest at the accident site and was consumed by a post-crash fire. The accident site was 1 mile west from the operator's airfield and base of operations. MEDICAL AND PATHOLOGICAL INFORMATION A postmortem examination was conducted by the Yuma County Medical Examiner, Yuma, Arizona, on December 3, 2014. The cause of death was reported as undetermined. The Federal Aviation Administration (FAA) Civil Aerospace Medical Institute performed forensic toxicology on specimens from the pilot; Carbon Monoxide and Cyanide testing were not performed, and no volatiles or drugs of abuse were detected. TEST AND RESEARCH The FAA, Air Tractor, and Pratt and Whitney – Canada examined the airplane at Air Transport in Phoenix, Arizona, on December 16, 2014. Visual inspection of the airframe revealed that the structure aft of the cockpit was intact; while forward of the cockpit had been destroyed by a post-crash fire. The airplane was equipped with AmSafe Inflatable Restraints. The flight control surfaces were all identified, and were damaged by the impact and post-crash fire; flight control continuity was established. There was no evidence of a pre-impact anomaly that would have precluded normal operation of the airframe or flight control systems. According to Air Tractor, the condition of the wreckage was consistent with a near-vertical impact with terrain with high forward G-impact forces. A detailed report is attached to the public docket for this accident. Examination of the engine revealed no pre-impact mechanical anomalies that would have precluded normal operation. The three-bladed Hartzell propeller was located with the main wreckage. One of the propeller blades remained attached to he propeller hub, and the other two propeller blades had separated from the propeller hub. All of the propeller blades showed evidence of S-bending. The engine inspection revealed that the engine had sustained severe impact damage, which included compressional deformation of the exhaust duct, and the gas generator case, along with the fracture of the inlet case support struts. The compressor turbine shroud, compressor turbine, interstage baffle, power turbine shroud, and the power turbine sustained circumferential rubbing and machining due to the impact. Both the compressor and power turbine blades were circumferentially fractured due to contact with the adjacent components.