Air Tractor AT502 N6113C accident near Sumner, Iowa

Probable cause

The pilot’s impairment by medical conditions and/or medications, which resulted in the airplane’s impact with power lines and terrain.

NTSB analysis

The pilot overflew the intended destination airport and continued about 14 miles north before turning to the south. Witnesses located about 2-1/2 miles north of the accident site reported observing the airplane overfly their homes at a low altitude. One witness noted that the airplane appeared to be in level flight, and the engine seemed to be operating normally.

A witness near the accident site observed the airplane approach from the west-northwest. The airplane struck power lines; however, the airplane's flightpath was not affected. The airplane then nearly struck a building before it struck a second set of power lines. It then veered left, and the nose dropped. The airplane subsequently impacted a road, skidded across the road, and impacted the ground near a large tree. A postimpact fire ensued. According to witnesses, there was nothing unusual about the airplane before the initial wire strike. The airplane seemed to be intact, and the engine sounded normal. The airplane remained in a shallow left turn as it struck the power lines and did not appear to be climbing or descending.

A postaccident airframe examination did not reveal any evidence of an in-flight structural failure or flight control system anomaly. An engine examination revealed circumferential contact marks throughout the engine consistent with rotation at impact. No anomalies consistent with a preimpact failure or malfunction were observed.

Review of the pilot’s medical records, toxicology testing, and autopsy results revealed that he was at significant risk of impairment from multiple serious medical conditions and the use of multiple potentially impairing medications. The pilot had heart disease, a subarachnoid hemorrhage that appeared to be several days old, chronic kidney disease treated with dialysis, poorly controlled diabetes, hypertension, chronic pain, and anxiety. In addition, the pilot was taking hydrocodone, fentanyl, trazodone, and yohimbine, any of which had the potential to be impairing.

Further, the investigation revealed that the pilot was involved in another wire strike event 8 days before the accident. Witnesses noted that after that wire strike, the pilot seemed shaken, and he was heard coughing and vomiting several days later. The timing of the pilot’s subarachnoid hemorrhage suggests that it may have resulted from this previous wire strike event. Although additional details about the events surrounding the wire strike are not known, the wire strike event itself suggests a possibility of some manifestation of pilot impairment that began before the accident flight.

While it could not be determined which specific medical factor or factors played a role in this accident, it is likely that one or more of the pilot's multiple medical conditions, medications, or the previous wire strike impaired his performance during the accident flight, as evidenced by his overflight of the intended destination airport and his continued low altitude flight in the vicinity of power lines and buildings without a change in flightpath or any apparent effort to avoid them.

Text from the NTSB. Open the NTSB docket for CEN19FA259 for the full record.