Accident Overview
On March 20, 2018, at about 1942 Alaska daylight time, a wheel-equipped, twin-engine, turbine-powered de Havilland DHC-6 (Twin Otter), registration N716JP, struck a pedestrian after takeoff from a remote sea ice airstrip approximately 140 miles north of Deadhorse, Alaska. The aircraft sustained substantial damage to the left wing and left aileron, and the pedestrian suffered serious head and neck injuries. The captain, first officer, and three passengers on board were uninjured. The flight was operated by Bald Mountain Air Service, Inc., of Homer, Alaska, under 14 Code of Federal Regulations Part 135 as a visual flight rules on-demand commercial flight.
Preaccident Events
The flight was providing logistical support for ICEX 2018, a U.S. Navy and U.K. Royal Navy submarine exercise under the Arctic Ocean. The airstrip, constructed on sea ice, consisted of a 2,500-foot-long by 75-foot-wide north/south runway intersecting with an east/west runway, both lined with snow berms. According to the captain, visibility was clear with ice pack haze; the sun was low on the horizon, creating shadows and flat light conditions that made topographical features difficult to discern.
Takeoff and Collision
The captain reported that after back-taxiing to the south end of the airstrip, both pilots observed the pedestrian standing near the departure end on the left side, close to the east/west runway intersection. During the takeoff roll to the north, the aircraft veered slightly left, and the captain applied differential engine power to correct. After becoming airborne, he lowered the nose to remain in ground effect and gain airspeed. As airspeed increased, he initiated a climb and then a left turn. During the turn, both pilots heard a loud thump, followed by an aileron control anomaly. The captain continued the turn and entered a left downwind traffic pattern for an emergency landing to the north. After landing, both pilots saw the pedestrian lying behind a snow berm on the left side of the airstrip. The captain reported no preaccident mechanical malfunctions or failures.
Pedestrian Account
The injured pedestrian, an employee of the Arctic Submarine Laboratory, stated in a hospital interview that before the pilots boarded, he discussed with the captain his plan to photograph the departure from alongside the airstrip. He positioned himself behind a snow berm, well clear of the strip, and placed figurines on the berm. He noted that the aircraft did not climb as quickly as during previous departures. He recalled seeing the left wing lower as the aircraft began a left turn toward him before losing consciousness.
Postaccident Investigation
A security video from a camp structure west of the runway recorded the accident in low, flat light conditions. The video showed the pedestrian standing near equipment and a snowmachine. As the low-flying aircraft entered the frame, it flew straight and level, then began a steep left turn with the left wing lowering, striking the pedestrian before continuing out of view. The aircraft's cockpit voice recorder was sent to the NTSB laboratory but failed to capture the accident events. The closest weather observation, from Deadhorse Airport at 1953, reported wind 270° at 12 knots, visibility 9 miles with light snow, scattered clouds at 2,900 ft, overcast at 4,600 ft, temperature -4°F, dew point -9°F, and altimeter 30.47 inHg.