Brantly B2 N5955X accident near St. Michael, Alaska

Probable cause

The pilot’s inadequate supervision of the refueling process, which resulted in a loss of engine power due to water contamination in the helicopter’s fuel system from the fuel drum and subsequent impact with terrain.

NTSB analysis

The pilot reported that, while in a high-hover profile conducting aerial reindeer herding operations, he decided to make a precautionary landing with the skid-equipped helicopter on "knee-high" tussocks in remote tundra due to several "left yaw movements" followed by an "uncommanded left yaw." The pilot initiated a hovering autorotation from about 15 ft above ground level. During the landing sequence, the left skid assembly was damaged, and the helicopter settled forward and to the left, which resulted in the three main rotor blades impacting the tundra. All three main rotor blades separated midspan due to the impact, and the helicopter sustained substantial damage to the main rotor system and fuselage.

After the accident, the pilot spoke with a witness who heard the engine producing "popping" noises and then "quit." At the time of the accident, the pilot reported he did not realize that the engine had lost power.

Postaccident examination of the airframe and engine by the pilot revealed no preimpact mechanical malfunctions that would have precluded normal operation. While inspecting the fuel cell, the pilot found 1/8 of a cup of water with about 5 gallons of fuel remaining.

During the aerial herding operations, the helicopter was shut down for refueling several times throughout the day, and no hot refueling operations were conducted. The pilot spoke with some local community members who were assisting him on the day of the aerial herding operations. The pilot found that, when the helicopter was last refueled before the accident flight and when the fuel was transferred from a steel drum with a pump system to a plastic jug for pouring in the helicopter, a water separating filter/funnel was not used by one of the local community members who was assisting the pilot with the refueling operations. The individual misunderstood the refueling operations and thought that the fuel filtering process would take place as the fuel was poured directly into the helicopter. Water was subsequently found in the steel drum that was used. The pilot reported that he conducted a preflight check of the helicopter's fuel cell (sump) before the accident flight, and no fuel discrepancies were observed at the time.

The Federal Aviation Administration published Advisory Circular 20-125, "Water in Aviation Fuels," which discussed the potential hazards of water in aviation fuels and stated, in part:

The pilot in command has the final responsibility to determine that the aircraft is properly serviced. The pilot in command should also be present during the refueling operation to inspect a sample of the fuel from the dispensing unit prior to fueling the aircraft.

Refueling from drum storage or cans should be considered as an unsatisfactory operation and one to be avoided whenever possible. All containers of this type should be regarded with suspicion and the contents carefully inspected, identified, and checked for water and other contamination.

Text from the NTSB. Open the NTSB docket for ANC17CA044 for the full record.