ERA17FA131

The pilot's incapacitation for reasons that could not be determined, which resulted in collision with trees and terrain.

The nearly 30,000-hour commercial pilot was conducting an aerial application flight. A nearby witness heard the airplane and reported that it sounded normal, then about 10 to 15 seconds later, he heard a "pop" sound followed by an explosion. Examination of the accident site, which was located well within the typical agricultural turn distance location for a turbine-powered airplane, revealed that the left wing collided with trees in a wings-level attitude. The airplane was destroyed by impact and a postcrash fire. No preexisting mechanical anomalies were noted with the airplane or its systems that would have precluded normal operation and propeller damage indicated that the engine was producing power at the time of impact. The pilot was reported by family members to have had a cold the day before the accident, and toxicology identified doxylamine, a sedating antihistamine, in the pilot's blood and urine. The pilot may have experienced impairing effects from the doxylamine, which could have affected his reaction time, sleepiness, and judgment. Although the autopsy did not identify any incapacitating medical conditions, there are a number of conditions that could incapacitate a pilot and leave no evidence at autopsy. The airplane's descent below the height of trees, the pilot's failure to avoid trees before impact, and his failure to use a nearby open field as a forced landing site suggest that he likely was unable to perform basic piloting functions, most likely due to incapacitation, although the reason for incapacitation could not be determined.

The Mississippi State Medical Examiner, Pearl, Mississippi, performed a postmortem examination of the pilot. No soot aspiration was noted in multiple sections of lung and bronchus. The cause of death was reported as "asphyxia of undetermined etiology." The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed forensic toxicological testing on specimens from the pilot. According to the toxicology report, no carbon monoxide was detected in the cardiac blood and no volatiles were detected in vitreous. Unquantified amounts of dextromethorphan, dextrorphan (metabolite of dextromethorphan), and pseudoephedrine were detected in cardiac blood and urine. An unquantified amount of doxylamine was detected in the urine specimen, and 0.145 ug/ml of the same drug was detected in cardiac blood. Acetaminophen (12.07 ug/ml) was detected in urine. Dextromethorphan is a cough suppressant available in many over-the-counter cough and cold preparations. Pseudoephedrine is a decongestant commonly marketed with the name Sudafed. Products containing this drug are only available "behind the counter" but do not require a prescription. Acetaminophen is an analgesic and fever reducer available over-the-counter and commonly marketed with the name Tylenol. These drugs are not considered impairing in usual doses. Doxylamine is a first-generation sedating antihistamine available over-the-counter in a number of products intended to treat colds, allergies, and insomnia. Doxylamine causes central nervous system depression and carries the warning, "May cause central nervous system depression, which may impair physical or mental abilities; patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery or driving)." The usual blood levels thought to be associated with effects from this drug are between 0.050 and 0.150 ug/ml. Doxylamine undergoes post mortem redistribution; central levels may be elevated above peripheral or antemortem levels by an average of about 2.5 times. At 1553, a surface observation at Greenville Mid-Delta Airport (GLH), Greenville, Mississippi, located about 18 nautical miles south-southwest of the accident site, reported calm wind, 10 miles visibility with clear skies, temperature and dew point 26°C and 8°C, respectively, and an altimeter setting of 30.21 inches of mercury. The pilot, age 68, held a commercial pilot certificate with a rating for airplane single-engine land. He held a Federal Aviation Administration (FAA) second-class medical certificate with a limitation to have available glasses for near vision, issued January 16, 2017. He reported 29,943 total hours of flight experience on the application for his last medical certificate. His last flight review in accordance with 14 CFR Part 61.56 occurred on January 30, 2017. The pilot was hired by the operator in March 2011. A review of his logbook revealed that about the time he was hired, he had accrued a total time of about 24,613 hours. His title at the time of the accident was Chief Supervisor/Pilot. The pilot's sister reported that she spoke with her brother the day before the accident, and during that call, he reported having a cold. The accident airplane was manufactured in 2012 by Air Tractor, Inc., and was designated serial number 602-1219. It was powered by a Pratt & Whitney Canada PT6A-60AG engine rated at 1,050 shaft horsepower for takeoff, and equipped with a Hartzell HC-B5MP-3C/M10876ANS propeller. Review of the maintenance records revealed that the airplane's last annual inspection was performed on November 8, 2016, at an airplane total time of 2,752 hours. The airplane was equipped with an AgJunction Satloc G4 GPS receiver capable of recording and retaining data; however, due to heat damage to the two internal memory cards, no data could be extracted from the device. The accident site was located among trees at the southern portion of an open field, about 760 ft east of the eastern edge of the 75-acre field the pilot intended to spray. Further examination of the accident site revealed damage to trees between 15 and 20 ft above ground level (agl) on a magnetic heading about 280°. Airplane debris was located on the ground among the trees and in the open field north of the energy path between the first tree contact and the main wreckage, which was located about 282 ft and 280° from the first tree contact location. Damage to trees at decreasing heights was noted along the energy path. The main wreckage had an odor of Jet A fuel. Components that were located farthest east from the fuselage included portions of the left wingtip, outboard end of the left main spar, leading edge of the left wing with semi-circular leading edge damage, outboard portion of the left aileron with outboard boom hanger bracket, section of left wing leading edge with pitot tube, and a section of the leading edge with semi-circular wrapping. The semi-circular impression on the leading edge of the left wing was correlated with a standing tree that exhibited impact damage. The wing damage and the lack of damage to the ground at the corresponding area of the right wingtip was consistent with a wings-level attitude at the time of tree impact. Examination of the airplane revealed extensive heat damage to the fuselage, cockpit, and sections of both wings that were not separated during the accident sequence. Both wings remained secured at the center splice, and all main spar attach bolts were sheared at the fuselage attach point but remained trapped. The inboard attach angle of the left wing was deformed, and both attach angles of the right wing were deformed. The left wing main spar was "S" shaped and the spar was fractured about 5 ft 10 inches outboard of the outboard wing splice. The aft spar of the left wing remained connected at the fuselage, but the spar was separated from the attach plate. The aft spar was fractured 6 ft 3 inches from the inboard section. The full span of the left wing leading edge was separated and/or consumed by fire. The left aileron trim tab was pulled from the aileron, but the pushrod remained connected. The pushrod was separated from the aileron trim tab actuator; therefore, the aileron trim position could not be determined. Examination of the right wing revealed that the aft spar remained attached, but the spar was heat damaged. The aft spar was identified to the outboard portion of the fuel tank, and then the outer portion at the wingtip. The aluminum portions of the main spar was heat damaged 5 ft 7 inches outboard of the spar splice. The cockpit sustained extensive fire damage; however, the occupiable space of the cockpit was not compromised. The right lower longeron was fractured, and the left side top door frame and left forward door post were cut during recovery. The pilot's seat remained fully attached and was equipped with shoulder harness airbags, which exhibited extensive heat damage. The control stick was not fractured, and the emergency dump handle was in the locked (non-dumping) position. The power, condition, and propeller controls were full aft, consistent with being pulled during separation of the engine. The flap actuator was separated and located on the ground near the cockpit area and was extended 4 threads, which equated to about 5° of flap deflection/extension. All primary and secondary flight control surfaces and their respective counterweights were accounted for. Flight control system continuity was confirmed for roll, pitch, yaw, and right aileron droop system though heat damage to pushrods and overload failure of cables and pushrods was noted. Examination of the left aileron droop system revealed separation of both pushrods at the aileron droop idler. The attaching hardware was not located. The rod end bearing cage of both rod ends was deformed in the aft direction consistent with the bolt diameter, and the idler bellcrank was deformed. The drooping arm on the ailero