ERA14FA066 · Texas Helicopter Corp M74L

After a day of aerial application flights, the pilot landed in a farm field and had the helicopter serviced with fuel from a truck before departing on the accident flight. A witness observed the helicopter descending toward an open field from an altitude about 150 feet above ground level. The helicopter then descended to about 50 feet, leveled briefly, then "fell" straight to the ground, and erupted in flames. The wreckage was partially consumed by a postimpact fire.

Examination of the wreckage following the accident revealed that the engine's carburetor float bowl was absent of fuel and contaminated with a rust-colored powder, which contained both ferrous and non-ferrous metal. Detailed examination of particulate matter collected from the filter housing of the fuel truck used to service the helicopter showed those components to be similarly contaminated. Additionally, during a postaccident demonstration of the procedure used to fuel the helicopter, the initial fuel dispensed was brown and gold in color. The operator of the fuel truck noted that it was typical to continue dispensing fuel into a separate container until it "turned blue," before beginning to fill the helicopter.

The extent to which the fuel onboard the helicopter at the time of the accident was contaminated could not be determined due to the extent of the post-impact fire and lack of available fuel samples from the helicopter. However; based on the powdered contamination recovered from the carburetor float bowl, it is likely that the fuel contamination was significant enough to result in a partial or total loss of engine power, which would have required that the pilot conduct an off-airport precautionary landing, or autorotation and forced landing.

The pilot's toxicology testing revealed a carbon monoxide level that was consistent with the autopsy findings of abundant soot in the upper and lower airways and indicated exposure to combustion products in the postimpact fire. It was unlikely that an elevated level of carbon monoxide was present in the pilot's blood before that crash. Toxicology testing also indicated that the pilot had used diphenhydramine before the accident. Diphenhydramine, a sedating antihistamine used to treat allergy symptoms and as a sleep aid. Diphenhydramine can cause marked sedation, altered mood, and impaired cognitive and psychomotor performance may. The pilot's diphenhydramine levels were above the therapeutic range, but may have been redistributed following death. Thus, it is likely the pilot had therapeutic levels of diphenhydramine in his system at the time of the crash. The pilot's time-critical decision-making and ability to perform an effective autorotation and/or landing were likely impaired by the use of diphenhydramine.

Verbatim NTSB analysis and probable cause from the NTSB dataset