Accident Details
On June 25, 2014, about 1447 Alaska daylight time, a float-equipped de Havilland DHC-2 airplane, registration N115CX, operated by RBG Bush Planes, LLC, struck a boat operator after takeoff from the Mulchatna River approximately 50 miles west of Iliamna, Alaska. The airline transport pilot was uninjured, the boat operator sustained serious injuries, and the airplane sustained minor damage. The flight was conducted under 14 Code of Federal Regulations (CFR) Part 91 without a flight plan. Visual meteorological conditions prevailed, and the flight was en route to Ekwok, Alaska.
Pilot Report
The pilot reported that two boat operators departed in separate boats downriver before he started the airplane. After clearing the area, he applied full throttle and proceeded westbound. He stated that after reaching step, he maintained a low altitude after lift-off to stay in ground effect while retracting flaps and increasing airspeed. After takeoff, he maintained altitude while traveling down the river. He saw one boat off his right side and believed the other boat would also remain to his right. Shortly after passing the first boat, he felt the plane sink, and when he pulled back on the yoke, he felt the back of the float strike something. The airplane had struck a boat operator, causing serious injury. The pilot continued, gained altitude, and returned to see one boat spinning in the middle of the river. He landed to assist, and the injured boat operator's boat subsequently collided with the airplane.
Witness Accounts
The other company pilot, who departed in a separate airplane, reported that he did not see the accident airplane at the time of the collision. When asked if mission or performance reasons required the accident airplane to be flown below 500 feet above ground level (agl) over the river or within 500 feet of the boat operators, he responded "no." The other boat operator told Alaska State Troopers that he was a few hundred yards upriver when he saw the accident airplane approach from behind, fly directly over him at about 15 to 20 feet, then drop lower and run straight into the other boat operator. He described the event as a "buzz job" and stated that the pilot had "buzzed us before."
GPS Data
A review of GPS data from the accident airplane's Garmin GPSMap 496 unit showed that after takeoff, the flight path followed the main channel and bends of the Mulchatna River, heading generally southwest and remaining low over the river. The river channel width varied from about 340 to 400 feet, with level, wooded banks. The straight-line distance from the initial GPS data point to the area where the airplane began a circling, climbing turn over land was about 1.6 nautical miles. The data indicated that after 1446:58, the airplane entered a left turn and gained altitude, diverging from the river. Subsequent data showed circling maneuvers and a descent with groundspeed slowing below flying speed. The final data points indicated groundspeeds below airplane flying speed near the area previously overflown.
Regulatory Context
Title 14 CFR 91.119(c) specifies that over areas not congested, except for takeoff or landing, an aircraft must maintain an altitude of 500 feet above the surface, except over open water or sparsely populated areas, where it must not operate closer than 500 feet to any person, vessel, vehicle, or structure. Title 14 CFR 91.13 prohibits operating an aircraft in a careless or reckless manner that endangers life or property.