WPR16FA029 · Airbus Helicopters AS350B3E

The private pilot and the pilot-rated passenger departed for a flight in the pilot's newly purchased helicopter. The pilot practiced several landings in a field during the flight and then flew back to the departure airport, where the approach and hover taxi to the ramp were uneventful. The pilot made a landing attempt on a dolly but landed only partially on the dolly, which caused the helicopter to pitch nose up and strike the ground with its tail. The helicopter hit the dolly with such force that the dolly broke free from the chocks securing it and spun around. The helicopter climbed and spun upwards aggressively but stabilized after rotating 270° to the right.

The pilot then landed the helicopter in an abnormal location that straddled the ramp and a taxiway. Ground crew personnel re-secured the dolly with chocks, and, after about 2 1/2 minutes, the pilot again attempted to land on the dolly, this time from the opposite direction. He made two unsuccessful attempts but was unable to maintain a stabilized approach each time. Although the pilot had the option to land on the ramp, he persisted in attempting to land on the dolly. On his third attempt, he again landed partially on the dolly, and the helicopter rocked back and forth striking the ground with its tailskid, before violently climbing and pitching nose down, while rolling right. The helicopter spun 180° to the left and pitched up steeply, and the tail rotor and vertical stabilizer struck the ground and separated. The helicopter hit the ground left side low, bounced, and rotated another 360° before landing hard on its belly. The main rotor blades continued to spin and the engine continued to operate; the helicopter spun on its belly at a rate of about one revolution per second for more than 5 minutes, while gradually sliding about 530 ft along the ramp. The tailboom and horizontal stabilizer then separated, and the helicopter violently rolled onto its side, shed its main rotor blades, and came to rest.

Onboard video showed that the pilot became incapacitated during the final ground collision. The passenger remained conscious after the impact and reached for the throttle on the pilot's collective control shortly after the helicopter started to spin, but the throttle position remained unchanged. He then attempted to brace himself against the glare shield, but he eventually became incapacitated after about 2 minutes due to his injuries, the forces imposed by the spinning helicopter, or both. He did not make any attempt to reach up for the engine-start selector or the fuel shutoff lever.

Postaccident examination did not reveal any anomalies with the helicopter's airframe or engine that would have precluded normal operation.

In the weeks preceding the accident, the pilot had expressed concern to multiple flight instructors that he was having difficulty adjusting to the flight characteristics of the helicopter. In particular, he found dolly-landings challenging.

Although the pilot had many years of experience flying a Bell 407 helicopter, there were two significant differences between the Bell 407 and the accident helicopter. First, their main rotor systems rotated in opposite directions; therefore, the foot pedal inputs required to counteract changes in torque during takeoff and landing were opposite. (The pilot's difficulty adapting to this difference was evidenced during most of the previous takeoffs captured by the onboard video when the helicopter yawed significantly after lifting off.) Second, the tips of the landing skids, which were used as a visual reference during landing, were forward of the pilot in the Bell 407 but just aft of the pilot in the accident helicopter. This change in visual reference would have been particularly significant during dolly landings, which require landing on a specific point directly below the pilot's field of view.

The pilot had received about 11 hours of flight instruction in the helicopter, and, despite the fact that his instructors advised him not to fly without an instructor, he opted to fly with a passenger instead of an instructor on the accident flight. Although the passenger held a helicopter rating, he was not an instructor or professional helicopter pilot and had about 180 hours total in helicopters. Furthermore, it was likely that he had little or no experience in the accident helicopter make and model.

The pilot's instructors reported a mobility problem with the pilot's left arm that affected his ability to reach overhead, but this problem likely did not contribute to the accident, because he had no need to reach overhead during landing. Postmortem toxicology testing identified amlodipine, valsartan, and rosuvastatin as well as diphenhydramine at 0.538 ug/ml and alprazolam at less than 0.05 mg/l in the pilot's blood. The pilot had heart disease and hypertension and used amlodipine, valsartan, and rosuvastatin for their treatment; however, these conditions and medications most likely did not contribute to the accident as they do not affect judgment or decision-making. Alprazolam is a significant central nervous system (CNS) depressant with the lower end of the therapeutic range at 0.0060 mg/l. The exact amount of alprazolam in the pilot could not be determined by testing and may have been very low.

The therapeutic range for diphenhydramine is 0.0250 to 0.1120 ug/ml. However, diphenhydramine undergoes postmortem redistribution, and postmortem central blood levels may increase by about three times. When divided by three or four, the pilot's postmortem level suggests that he had therapeutic levels at the time of the crash. Compared to other antihistamines, diphenhydramine causes marked sedation and is also a CNS depressant. In addition, it may cause altered mood and impaired cognitive and psychomotor performance. The use of two CNS depressants simultaneously typically results in cognitive impairment which is magnified well beyond the simple addition of the effects, even when the amount of one of them may be low. Therefore, the pilot's decision-making, judgment, and psychomotor performance were most likely impaired by the combination of CNS depressants, diphenhydramine and alprazolam.

Verbatim NTSB analysis and probable cause from the NTSB dataset