History of Flight
On November 30, 2014, at approximately 0115 mountain standard time, an Air Tractor Inc. AT-502B (registration N946TR) impacted an open field near Somerton, Arizona. The airplane was operated by Tri Rotor Spray and Chemical, Inc. under 14 CFR 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 flight departed from a private airstrip about 0110. Visual night meteorological conditions prevailed, and a company flight plan had been filed.
According to a company representative, prior to the accident the pilot had landed, placed 100 gallons of water onboard, and intended to perform a water calibration flight. After spraying water on a field, the pilot was returning to land. No radio communications were made between the pilot and other company pilots in the area before the accident.
A company pilot saw a flash while taking off. He flew toward the flash and observed an airplane engulfed in flames. He landed near the accident site but could not approach due to the flames. Six pilots in the area reported small areas of patchy fog; estimates placed the fog layer between 150 and 400 feet above ground level with good visibility.
Personnel Information
The pilot, aged 55, held a commercial pilot certificate with ratings for airplane single- and multi-engine land, instrument airplane, and helicopter. He held a second-class medical certificate issued September 23, 2014, with a requirement to wear corrective lenses. On his medical application, he reported 12,200 total flight hours, with 45 hours in the preceding 6 months. His last flight review was March 18, 2014, performed in a Bell 206B.
Aircraft Information
The single-engine, low-wing, conventional-gear Air Tractor AT-502B (serial number 502B-2946) was equipped with a Pratt and Whitney PT6A-34AG turboprop engine. According to the operator, a 100-hour inspection was performed on November 2, 2014. Airframe total time was 502.2 hours; the engine had 20 hours since last inspection.
Meteorological Information
A weather study by an NTSB senior meteorologist reported a moist layer in the low farming region. Temperature was 50.7°F, dew point 48°F, relative humidity 91%. The fog layer was not extensive and was not observed at Yuma, Arizona, nor on satellite imagery. Aircraft soundings indicated a strong surface-based temperature inversion with light winds, below favorable for light fog or mist formation. No National Weather Service advisories for extensive IFR conditions, low-level windshear, or turbulence were in effect.
Wreckage and Impact Information
The accident site was at the intersection of County 18-3/4's street and Avenue E South in an open field, with no obstacles identified. The entire airplane came to rest at the site and was consumed by postcrash fire. The site was 1 mile west of the operator's airfield.
Medical and Pathological Information
A postmortem examination by the Yuma County Medical Examiner on December 3, 2014, listed the cause of death as undetermined. FAA forensic toxicology on pilot specimens detected no volatiles or drugs of abuse; carbon monoxide and cyanide tests were not performed.
Test and Research
Examination of the airframe at Air Transport in Phoenix, Arizona, on December 16, 2014, involved the FAA, Air Tractor, and Pratt & Whitney Canada. The structure aft of the cockpit was intact; forward of the cockpit was destroyed by fire. The airplane was equipped with AmSafe Inflatable Restraints. Flight control surfaces were identified, damaged by impact and fire, but continuity was established. No pre-impact anomaly precluding normal operation was found. According to Air Tractor, the wreckage condition was consistent with a near-vertical impact with high forward G-forces.
Engine examination revealed no pre-impact mechanical anomalies. The three-bladed Hartzell propeller showed one blade attached to the hub; two had separated. All blades exhibited S-bending. The engine sustained severe impact damage, including compressional deformation of the exhaust duct and gas generator case, fracture of inlet case support struts, and circumferential rubbing/machining of turbine components. Compressor and power turbine blades were circumferentially fractured due to contact with adjacent components.