ANC11TA110

The commercial helicopter pilot, with two passengers aboard, was supporting a snow survey crew atop an expansive, smooth, featureless, and snow-covered glacial ice field. This operation required brief stops at various predetermined sites along a prearranged route. When the pilot departed from one site en route to the next predetermined site, deteriorating weather conditions coupled with flat light conditions hampered his ability to see the topographical features of the ice field below. As the pilot slowed the helicopter to make a precautionary landing, the helicopter “touched down early.” After the initial touchdown, the pilot hover-taxied the helicopter to an area about 20 or 30 yards beyond the initial touchdown point, then he landed the helicopter in the deep snow. After landing, the helicopter tipped backwards as the aft portion of the skids settled into the deep snow, and the tail rotor blades subsequently struck the snow. The operator reported no preaccident mechanical problems with the helicopter. Before the helicopter could be ferried from the site, a maintenance technician inspected the helicopter for damage. Finding no apparent damage, the helicopter was started, ground run, and then hovered. While hovering, a tail rotor driveshaft coupling separated, and the pilot did a hovering autorotation back to the snow-covered ice field. As a result of the tail rotor driveshaft coupling separation, the helicopter sustained substantial damage to the tail rotor drive shaft assembly. The damage to the tail rotor drive shaft occurred as the helicopter was being ferried from the site, not during the original event. Most likely the drive shaft was degraded during the first landing, but it did not separate until the ferry flight.

On September 23, 2011, about 1330 Alaska daylight time, a high skid-equipped Bell 206B3 helicopter, N204PA, sustained substantial damage during a tail rotor strike while maneuvering to land on the Harding Ice Field, about 10 miles west of Seward, Alaska. The helicopter was owned and operated by Pathfinder Aviation, Homer, Alaska, as a visual flight rules (VFR) public use passenger flight, in conjunction with the National Park Service (NPS), under the provisions of 14 Code of Federal Regulations Part 135, when the accident occurred. The commercial pilot and the two passengers were not injured. Visual meteorological conditions prevailed at the time of departure, and company flight following procedures were in effect. The flight originated about 1320 from a remote site on the Harding Ice Field. According to the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the operator, dated October 25, along with subsequent conversations with Pathfinder Aviation’s director of operations, the purpose of flight was to transport two NPS employees to a remote snow-covered site on the Harding Ice Field to collect snow samples. The mission required brief stops at various predetermined sites along a prearranged route. The director of operations noted that when the pilot departed from the previous site, en route to the next predetermined site, weather conditions were “good VFR.” As the flight progressed towards the upper elevations of the ice field, the pilot encountered overcast layers and flat light conditions. According to the director of operations, as the pilot slowed the helicopter to make a precautionary landing, and while on approach, “the aircraft touched down early.” After the initial touchdown, the pilot hovered-taxied the helicopter to an area about 20 or 30 yards beyond the initial touchdown point, then he landed the helicopter in the deep snow. After landing, the helicopter tipped backwards as the aft portion of the skids settled into the deep snow, and the tail rotor blades subsequently struck the snow. There were no preaccident mechanical problems reported with the helicopter. In a written statement to the NTSB dated September 24, a passenger aboard the accident helicopter reported that while traveling from one landing site on the Harding Ice Field to another, visibility deteriorated rapidly, making it very difficult to discern any topographic features of the snow-covered ice field. He said that as the pilot began slowing the helicopter, he estimated the helicopter’s height above the ice to be 100 feet, and then the helicopter unexpectedly touched down. After the initial touchdown, the helicopter continued to hover momentarily, then the pilot immediately landed the helicopter, and it tipped backwards. Photos of the accident site were provided to the NTSB as part of the passenger’s written statement. The topographical features surrounding the accident site consisted of expansive, smooth, featureless, and snow-covered slopingterrain. According to Pathfinder Aviation’s director of operations, a company maintenance technician was flown by helicopter to the site to inspect the helicopter for damage before it could be ferried back to Seward. Finding no apparent damage, the helicopter was started, ground run, and then hovered. While hovering, a tail rotor driveshaft coupling separated, and the pilot did a hovering autorotation back to the snow-covered ice field. As a result, the helicopter sustained substantial damage to the tail rotor drive shaft assembly. In the recommendations section of the NTSB 6120.1 form submitted by the operator, the director of operations noted that future pilot training would include formal flat light and whiteout training, as well as added training on judgment and decision making regarding weather.