HISTORY OF FLIGHTOn April 9, 2019, about 1033 central daylight time, an Air Tractor AT-502 airplane, N7314D, was destroyed when it was involved in an accident near Harlingen, Texas. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 agricultural flight without a flight plan.

The purpose of the flight was to spray pesticide over a cultivated cotton field. There were multiple witnesses who saw the low-flying airplane collide with power transmission lines as it descended into the field to be sprayed. One individual saw the airplane flying east before it made a “sharp right turn” back toward the west and the field to be sprayed. The airplane pitched down and flew over the highway from east-to-west at a low altitude. The airplane then collided with power transmission lines and exploded when it hit the ground. PERSONNEL INFORMATIONThe pilot's flight history was established using his logbook. He began flying agricultural operations in April 1965, and his first flight in an Air Tractor AT-502 airplane was in September 1987. He logged at least 7,500 flight hours in the accident airplane. The final logbook entry was for a flight review dated March 24, 2016, at which time he had logged about 27,400 total flight hours. AIRCRAFT INFORMATIONThe airplane's hour meter was destroyed during the postimpact fire, which prevented a determination of the airplane's total service time at the time of the accident. A review of the maintenance records found no history of unresolved airworthiness issues. The operator reported that the airplane departed with 170 gallons of Jet-A fuel and 75 gallons of Malathion pesticide. AIRPORT INFORMATIONThe airplane's hour meter was destroyed during the postimpact fire, which prevented a determination of the airplane's total service time at the time of the accident. A review of the maintenance records found no history of unresolved airworthiness issues. The operator reported that the airplane departed with 170 gallons of Jet-A fuel and 75 gallons of Malathion pesticide. WRECKAGE AND IMPACT INFORMATIONThe accident site was in the cotton field that the pilot intended to spray. The airplane impacted two 1.108-inch diameter, 345-kilovolt power transmission cables strung between two 136 ft tall structures along the eastern border of the field. The airplane subsequently impacted the field about 200 ft west of the powerlines (Figure 1). A fan-shaped wreckage debris field extended about 100 ft from the initial ground impact. The overall distribution of the wreckage was consistent with the airplane traveling west-northwest when it impacted the ground. Red navigation lens material from the left wingtip was found at the initial impact with the ground.

The main wreckage consisted of the fuselage, empennage, right wing, engine, and propeller. The main wreckage exhibited evidence of a prolonged postimpact ground fire. The fuselage was found upright with significant fire damage. All airframe structural components and flight control surfaces were identified at the accident site. Flight control continuity could not be established due to damage; however, all observed separations were consistent with overstress or damage sustained during the postimpact fire. The left wing was highly fragmented during impact. There were two transmission cables conjoined with the main wreckage; one wrapped around the engine and propeller shaft, and the other wrapped around the wing carry-through structure, right wing, and fuselage (Figure 2 and Figure 3). The forward face of the left main wing spar exhibited broad vertical marks 3-6 ft from the airplane centerline that were consistent with contact with a large diameter power transmission cable (Figure 3). The right wing was largely intact with fire damage to the inboard portion of the wing.

Figure 1. Main Wreckage and Impact Debris Path

Figure 2 – Power Transmission Cables Conjoined with Main Wreckage (red arrows point to cables)

Figure 3 – Power Transmission Cables Conjoined with Right Wing (Left Image) and Cable Impact Marks to the Forward Face of the Left Main Wing Spar (Right Image)

Engine control continuity could not be established due to impact and fire damage. The first-stage compressor blades exhibited a tip rub and ingested dirt and organic matter. The engine was separated at the C flange to review the turbine section. The downstream side of the compressor turbine disc and blades exhibited rotational scoring from contact with the power turbine vane and baffle. A majority of the power turbine blades had separated from the disc. Several power turbine blade roots and tips were found preceding the main wreckage in the debris field. The remaining turbine blades were displaced forward in the disc and were fractured close to midspan of the airfoil. The disc and blades exhibited rotational scoring on the upstream side from contact with the power turbine baffle and vane. The downstream side of the power turbine blades and disc exhibited rotational scoring from contact with the exhaust duct.

The propeller remained attached to the engine. The three propeller blades remained attached to the hub and exhibited spanwise twisting. Two blades segmented during the impact sequence and one blade remained intact with leading and trailing edge gouging near the blade tip. The intact blade also exhibited minor chordwise scratches about midspan.

The postaccident examination did not reveal any anomalies that would have precluded normal operation of the airplane before it collided with the high-voltage power transmission lines. MEDICAL AND PATHOLOGICAL INFORMATIONAn autopsy of the pilot was performed by the Cameron County Forensic Department, Harlingen, Texas, which identified the cause of death as blunt force trauma. No significant natural disease was identified during the autopsy. Toxicological testing, completed by the Federal Aviation Administration’s Forensic Sciences Laboratory, identified 0.605 µg/mL of diphenhydramine in blood and detected diphenhydramine liver samples. No carboxyhemoglobin or ethanol was detected in blood samples. Diphenhydramine is a sedating antihistamine (commonly marketed as Benadryl) and is available over the counter in many products commonly used to treat colds, allergies, and insomnia. The therapeutic range is 0.025 to 0.100 µg/mL and it has a half-life of 3 to 14 hours. Diphenhydramine undergoes postmortem distribution and central levels may be two-to-three times higher than peripheral levels.