American Eurocopter AS350B2 N606HD

The helicopter accident occurred during an electronic news gathering (ENG) flight in night visual meteorological conditions. Weather and visibility at the time were good, and though the helicopter had been operating at or near the freezing level, no clouds or precipitation existed along its flightpath. Other air traffic did not appear to be a factor. The pilot and non-pilot videographer departed about 41 minutes before the accident on their third flight of the day. The non-pilot videographer was seated in the back of the helicopter, without access to the flight controls. They arrived at the scene of the assignment about 20 minutes after departing, collected video for about 10 minutes, and then began heading back to base. Up to this point, there were no anomalies with the flight. About 3 minutes before the accident, the helicopter drifted right of its established flight track and passed through its outbound course. Within 1 minute, the helicopter began to descend from an altitude of about 1000 ft mean sea level (msl). The gradual descent continued for about 2 minutes, with the ground speed gradually increasing. The helicopter then impacted terrain and a postimpact fire ensued. Examination of the wreckage did not reveal any evidence of a preimpact failure or malfunction of the helicopter, engine, or its systems that would have precluded normal operation. Examination of the wreckage also did not reveal any evidence of a bird strike. The flight profile, though, was consistent with the pilot becoming incapacitated or falling asleep. The pilot had a history of prediabetes, and toxicological evidence indicated he had used the blood-sugar-controlling medication metformin. His negative urine and vitreous glucose results indicated that he was unlikely to have been experiencing markedly elevated blood sugar at the time of the crash. The glucose results neither excluded nor supported a hypothesis of low blood sugar related to diabetes/prediabetes medication use; however, metformin use is not likely to result in symptomatic low blood sugar. Thus, there is no specific evidence that the pilot’s blood sugar was a factor in the accident. The pilot also had a history of high blood pressure treated with multiple medications. His toxicology results indicated that he had used the blood pressure medications telmisartan, hydrochlorothiazide (HCTZ), and carvedilol. Detected chlorthalidone likely was an impurity in the HCTZ rather than a fourth medication. Although the pilot’s blood pressure medications would not typically be impairing, his high blood pressure conveyed some increased risk of him experiencing an impairing or incapacitating cardiovascular event. However, there is no way to determine whether such an event occurred from the limited autopsy evidence. The combination of tadalafil and alfuzosin use, along with the multiple blood pressure medications, may also have conveyed some increased fainting risk, but this would have depended on multiple unknown variables, as tadalafil and alfuzosin are not typically impairing. Therefore, the only medication detected on postmortem toxicology that had typical impairing effects was chlorpheniramine. Although the measured level of chlorpheniramine in cavity blood could not be reliably related to specific effects, it indicated a possibility that the pilot may have been experiencing some associated sedation or psychomotor slowing. This may have made the pilot more susceptible to falling asleep. Chlorpheniramine effects also may have generally impaired his task performance, although it is less obvious how such impairment would explain the accident circumstances involving an extended period of uneventful flight followed by 3 minutes of unusual flight. Whether the pilot was using chlorpheniramine for a distracting or otherwise impairing condition is unknown. Overall, the pilot had medical conditions and had used medications that were associated with increased risk of impairment or incapacitation. However, there was insufficient medical evidence for the investigation to establish whether the pilot was incapacitated, or, if he was, the specific reason for his incapacitation.

Quoted verbatim from the NTSB record.