CEN18FA391

The pilot's failure to maintain main rotor speed after setting the engine fuel control to idle, which resulted in a loss of helicopter control and impact with water.

The private pilot had just purchased the helicopter and was returning it to his home airport accompanied by a commercial-certificated safety pilot and two passengers. Video from the cockpit image recorder indicated that the pilot, seated in the right seat, was manipulating the flight controls from takeoff until the accident occurred. The surviving passenger stated that, while en route, the pilot indicated that they would be landing on a beach in order to stretch their legs. The recovered data showed the helicopter flying about 500 to 700 ft over water when the pilots began conversing and pointing toward the shore. The safety pilot, whose hands were on his lap, then raised his right hand in a manner that appeared that he was guarding the cyclic control in anticipation that his assistance or intervention might be required. Shortly thereafter, the pilot twisted the collective twist grip throttle from FLIGHT to IDLE; data from the engine data recorder (EDR) indicated that, at this time, the engine fuel control was set to the idle power setting. Such action is consistent with a practice autorotation. The collective control was adjusted downward slightly, but the main rotor speed (Nr) gauge showed Nr decay from the normal "green" operating range of 375 to 405 rpm to the "yellow" cautionary range of 320 to 375 rpm about 5 seconds after the twist grip was set to IDLE. An Nr value of less than 360 rpm would have resulted in a continuous aural tone to alert the pilots of the low rotor speed. About 7 seconds after the twist grip was set to IDLE, the pilot reached toward the center console, after which the "HORN" caution light illuminated, consistent with the pilot muting the aural tone signaling the low Nr condition. After the horn was muted, Nr continued to decay to a low of 254 rpm. Several small cyclic inputs were observed, then the recorded data ended. The helicopter impacted the water and was destroyed. The four occupants were ejected from the helicopter; one of the passengers survived the accident and swam to shore. Postaccident examination of the helicopter and the recovered data did not reveal any helicopter malfunctions or failures that would have precluded normal operation. Since recorded cockpit imagery did not capture microphone audio, the reason for the pilot's decision to roll the throttle to IDLE could not be determined, and what conversations the pilots may have had before and during the maneuver could not be determined. The passengers' headphones were muted from the pilots' conversation, and the surviving passenger did not know if they planned to practice an autorotation to the beach. Cockpit video recordings from previous flights indicated that the safety pilot did not guard the flight controls when the pilot was performing takeoffs or landings. It is plausible that the pilot's intention was to practice or perform an autorotation to the beach, with the safety pilot guarding the controls. However, the beach was not the most suitable location for a practice autorotation to landing procedure and was out of the ordinary from their previous flights, as observed on the recorded cockpit imagery. When the twist grip throttle is set to IDLE position during normal flight, Nr will decay unless the pilot takes action to maintain it, such as a reduction in main rotor collective pitch or returning the twist grip throttle to the FLIGHT position. However, after the throttle was set to IDLE, the pilot failed to reduce main rotor collective pitch, which resulted in low rotor rpm. The pilot's action of muting the low rotor rpm alert horn indicated that he was aware of the annunciation to an anomalous condition, but it could not be determined if the pilot understood the nature of why the horn annunciated or the criticality of the situation.

The National Weather Service (NWS) Alaska Aviation Weather Unit issued flying weather graphics, which forecast marginal visual flight rules and no low-level turbulence for the accident area. The FAA Aviation Weather Cameras for YAK and Cape Spencer, Alaska, revealed a broken to overcast cloud layer and clear visibility around the time of the accident flight. The Appareo Vision 1000 onboard the helicopter showed brief periods of light rain on the helicopter's windscreen. The rain stopped about 7 minutes before the accident. The pilot began his helicopter flight training in a Robinson R44 helicopter and had accumulated 59 hours of helicopter flight experience. On forms provided to Airbus before conducting AS350-B3e model transition training, the pilot reported no experience in the accident helicopter make and model. On June 4, 2018, the pilot completed transition training for the AS350-B3e with an Airbus Helicopters flight instructor at the Airbus factory in Grand Prairie, Texas; this training included 3 hours of flight time and 1 hour of simulator time. From June 18 to August 29, 2018, the pilot completed at least 10 flights (more than 18.3 hours) in an AS350-B2 model operated by the safety pilot's company in Alaska. in Alaska. Of the 18.3 hours, 11.4 were conducted with the accident safety pilot and 6.9 were conducted with a company flight instructor. On August 5, 2018, the pilot completed a 1.5-hour flight at the Airbus factory with the same Airbus Helicopters flight instructor in an AS350-B3e. The pilot had accumulated 4.5 flight hours in the B3e before departing Texas with the accident helicopter. The safety pilot was the owner, director of operations, and chief pilot for two different commercial helicopter operators in Alaska that operated several AS350-B2 model helicopters. The surviving passenger was not a pilot, but he did attend helicopter ground school classes with the accident pilot and had knowledge of helicopter procedures and helicopter flight theory. The passenger stated that, when taking delivery of the accident helicopter in Texas, the safety pilot did not seem recently familiar with the B3e model and the options that were installed on the accident helicopter. The safety pilot asked a lot of questions about the B3e, and the pilot appeared more familiar with the helicopter systems than the safety pilot. The Alaska State Medical Examiner's Office, Anchorage, Alaska, conducted an autopsy of the safety pilot. The autopsy report concluded that the cause of death was multiple blunt-force injuries. The autopsy revealed severe coronary artery disease with 75% stenosis of the left anterior descending coronary artery. There was no thromboembolus and no evidence of a recent or past heart attack. There were no autopsy findings to suggest an incapacitating event; additionally, the recorded images from the Vision 1000 revealed that the safety pilot was conscious and functioning at the time of the accident. Toxicological testing of urine specimens by the FAA Forensic Sciences Laboratory detected no drugs or ethanol. The pilot's body was not recovered. The Airbus Helicopters was equipped with a three-bladed main rotor system and a two-bladed tail rotor system. The flight controls are were hydraulically assisted by a dual hydraulic system. The helicopter was equipped with both pilot and safety pilot controls and a Genesys Aerosystems HeliSAS autopilot and stability augmentation system. The collective-mounted engine control twist grip throttle contains two positions: IDLE and FLIGHT. In the normal procedures section of the AS350 B3e rotorcraft flight manual (RFM), the twist grip throttle is moved from the IDLE position to the FLIGHT position during the run-up checks. The twist grip throttle remains in the FLIGHT position until the postlanding engine and rotor shutdown procedures are performed. When the twist grip throttle is outside of its FLIGHT position, a "TWT GRIP" warning light illuminates on the cockpit caution and warning panel (CWP). According to Airbus Helicopters, the airframe and engine had accumulated a total time of 13.7 hours at the time of delivery. An estimated 25-30 hours was accumulated from delivery until the accident. On September 28, 2018, at 1057 Alaska daylight time, an Airbus Helicopters AS350-B3e helicopter, N907PL, was destroyed when it was involved in an accident in Glacier Bay National Park, about 60 miles northwest of Gustavus, Alaska. The safety pilot was fatally injured, one passenger sustained serious injuries, and the pilot and another passenger remain missing and are presumed fatal. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The purpose of the trip was to deliver the newly-purchased helicopter to Anchorage from the Airbus Helicopters factory in Texas. The left seat safety pilot was onboard for insurance coverage purposes and was acting as a safety pilot. The right seat pilot-in-command, who owned the helicopter, planned to drop off the safety pilot in Wasilla, Alaska, then proceed to Anchorage with the passengers. The trip began on September 25, 2018, and included more than 30 stops for sightseeing, fuel, and rest. In a postaccident interview, the surviving passenger, who was seated in the left rear seat, stated that the accident flight departed Juneau International Airport (JNU), Juneau, Alaska, and proceeded north toward Yakutat Airport (YAK), Yakutat, Alaska, at low altitude parallel to the shoreline. The passengers' headphones were muted, but at one point, the pilot unmuted the passengers' headphones and asked if the passengers wanted to land on a beach to stretch their legs. About 1 minute later, the safety pilot pointed his hand to the right toward a long stretch of beach. The passenger recalled that the pilot initiated a controlled right turn and the helicopter began to descend; the safety pilot did not have his hands on the flight controls. He stated that the pilot pulled up on the collective and rolled the throttle off. He never heard anything abnormal with the engine noise or noticed any anomalies with the helicopter. The pilot left the collective up and the helicopter entered a free fall from about 500 ft agl, then about 30 ft agl the pilot increased the throttle again. Before impact, he heard the pilot yell "NO" and continue to manipulate the flight controls. He felt the helicopter impact the water and noticed water splash in the cabin before he lost consciousness. He later awoke in the water and swam to shore, where he awaited rescue. He was unable to locate the other occupants. A review of the onboard cockpit image recorder, an Appareo Vision 1000, revealed that the helicopter was refueled at JNU before departing on the accident flight. The helicopter departed JNU and proceeded west over the mountains about 3,000 to 4,000 ft mean sea level (msl), then northwest along the coastline about 500 to 700 ft msl. Figure 1 depicts the helicopter's flight path from JNU to the accident site. Figure 1 – The helicopter flight track in orange from JNU to the accident site. The main fuselage was found on a beach on its left side and partially embedded in the sand as shown in Figure 3. The structure forward of the aft cabin bulkhead had separated from the main fuselage. The left and right aft bench seats remained attached to the aft cabin bulkhead. The two longitudinal floor beams for the cabin floor structure were fractured several inches forward of the aft cabin bulkhead. The rear structure of the main fuselage was crushed inward throughout its circumference. The engine firewall remained attached to the main fuselage; its base was deformed in the aft direction and its upper portion was partially fractured. The engine deck was deformed downward. The engine air inlet barrier filter remained installed within its frame, but the cowling surrounding the frame had separated. Sand was found within the barrier filter.