Eurocopter AS 350 B2 accident near Eufaula, Oklahoma, March 13, 2015

The NTSB's narrative final · quoted from the NTSB record

The commercial pilot was conducting a positioning flight back to the base after conducting an emergency medical services flight during which a patient was transported to a hospital. According to one of the two medical crewmembers onboard the flight, the crew checked the weather before the flight, and the report showed ceilings at 8,500 ft. and 6 miles visibility at their intended destination and ceilings at 10,000 ft. at the departure location. During the flight to transport the patient, the pilot stated that the clouds above their cruise altitude were lower than he expected. The pilot descended the helicopter and landed it at the hospital helipad without incident. While on the ground, the pilot checked the weather conditions again, and they were the same. After the pilot conferred with the medical crew per their risk management procedures, they decided to return to their base as planned. During the accident flight, the helicopter was southbound at a cruise altitude of about 1,500 ft. mean sea level (msl) in an area with a terrain elevation of about 700 to 900 ft. msl, and dark night visual meteorological conditions existed. According to the medical crewmembers, about midway to their destination, the helicopter entered instrument meteorological conditions (IMC). After a brief discussion, during which one of the crewmembers told the pilot to go "up," the pilot stated he was going to divert to another airport because he saw lights, and he then began a left turn. Although both crewmembers reported seeing trees and one of them told the pilot to "pull up," shortly after , the helicopter impacted trees and terrain atop a wooded hill at an elevation of about 840 ft. msl, which resulted in the separation of the tailboom and portions of the fuselage; the main wreckage came to rest on its right side. A meteorological reporting station located about 20 miles north-northwest of the accident location reported a broken ceiling at 2,400 ft. above ground level (agl) and 10 statute miles visibility at the time of the accident. Another meteorological reporting station located about 28 miles south of the accident location reported cloud bases between 900 and 2,100 ft. agl at the time of the accident. An examination of the helicopter revealed no preimpact anomalies that would have precluded normal operation. It is likely that the pilot experienced special disorientation during a turn after inadvertently entering IMC, which resulted in the helicopter descending into trees atop high terrain. Zolpidem, which is a prescription hypnotic medication used to treat insomnia and may impair mental and/or physical ability required to perform potentially hazardous tasks such as driving or operating heavy machinery, was detected in the pilot's blood and liver. Given it was not detected in the central blood, it could not be determined whether or to what extent it might have impaired the pilot .

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.