WPR13LA303

The pilot reported that, while making a shallow approach to the water to fill a water bucket in preparation for his fourth water drop, he was looking down at the bucket, and, just as the bucket went into the water, the helicopter began "settling [with power]." The pilot corrected the condition by moving the cyclic right and forward and descending the helicopter, which placed it "back in good air" and then moved the helicopter forward. With the bucket in the water, the pilot pulled the cyclic aft as the line became tight. However, the helicopter's nose dropped very low instead of rising as expected, and the main rotor struck the tail. The helicopter subsequently started spinning right likely because the main rotor strike had severed the tail rotor drive shaft, and, after two or three turns, the pilot realized that he could not control the helicopter, so he rolled off the throttle, which stopped the spin. The helicopter then descended and contacted the water hard. The pilot determined that he had not taken into account that the river had moved the bucket downstream, and, as a result, the bucket was behind (not directly below) the helicopter, which caused the helicopter's nose to pitch down when the line became tight. The pilot reported no mechanical anomalies with the helicopter that would have precluded normal operation, and he stated that the wind was calm at the time of the accident.

On June 28, 2013, about 1308 mountain daylight time, a Bell 206L-3 helicopter, N868H, was substantially damaged following impact with terrain while maneuvering near Missoula, Montana. The commercial pilot was seriously injured. The helicopter was registered to and operated by Hillcrest Aircraft Company in accordance with 14 Code of Federal Regulations Part 133 as a proficiency check flight. Visual meteorological conditions prevailed at the time of the accident, and a flight plan was not filed. The helicopter had departed the Missoula International Airport (MSO), Missoula, Montana, about 1200.In a statement submitted to the National Transportation Safety Board investigator-in-charge, the pilot reported that on the day of the accident he was undergoing an evaluation by a United States Forest Service (USFS) evaluator. After demonstrating basic flying techniques with the USFS evaluator on board, the pilot landed on a sandbar to let the evaluator deplane. The pilot subsequently took off, made 3 water drops, and on the planned 4th water drop made a shallow approach to the water. The pilot stated that while looking down at the bucket, and just as the bucket went into the water, "…things did not feel right." The pilot opined that he knew immediately that he was "settling [with power]." The pilot reported that at this point he thought that with 150 feet of line, he could descend enough to get into good air without dropping the bucket. He then reduced collective slightly, moved the cyclic right and forward, descended, and was in good air and moving forward. The pilot stated that when he pulled aft cyclic as the line became tight, the nose of the helicopter went very low and he felt the [main] rotor strike the tail, which created a very bad vibration. As he moved the helicopter closer to the shoreline the vibration stopped, however, this was followed by the aircraft starting to spin to the right. The pilot reported that after 2 or 3 turns when he realized that he could not control the helicopter sufficiently to get it to the shoreline, he rolled the throttle off and the spin stopped, followed by the aircraft descending and making hard contact with the water. The pilot concluded that he had not taken into account that the river had moved the bucket downstream. Damage to the helicopter included the tail boom, vertical stabilizers, tail rotor drive shaft, aircraft belly/tub, and skid gear tubes. The pilot reported no anomalies with helicopter that would have precluded normal operation. At 1253, the MSO weather reporting facility, located about 1 nautical mile northeast of the accident site, reported wind calm, sky clear, temperature 28 degrees Celsius (C), dew point 11 degrees C, and an altimeter reading of 30.26 inches of mercury. The Federal Aviation Administration Helicopter Flying Handbook (FAA-H-8083-21, Chapter 11, p. 11-13) states, "Vortex ring state" is an aerodynamic condition in which a helicopter may be in a vertical descent with 20 percent, up tomaximum power applied, and little or no climb performance. "Settling with power" occurs when the helicopter keeps settling even though full engine power is applied. Main rotor tip vortices generate drag and degrade airfoil efficiency. As long as the tip vortices are small, their only effect is a small loss in main rotor efficiency. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the tip vortices. In this vortex ring state, most of the power developed by the engine is wasted in circulating the air in a doughnut pattern around the rotor. A vortex ring state may be entered during any maneuver that places the main rotor in a condition of descending in a column of disturbed air and low forward airspeed. Airspeeds that are below translational lift airspeeds are within this region of susceptibility to settling with power aerodynamics. This condition is sometimes seen during quick-stop type maneuvers or during recovery from autorotation. Some of the situations that are conducive to a settling with power condition are hovering above ground effect altitude, specifically attempting to hover out of ground effect (OGE) at altitudes above the hovering ceiling of the helicopter, attempting to hover OGE without maintaining precise altitude control, pinnacle or rooftop helipads when the wind is not aligned with the landing direction, and downwind and steep power approaches in which airspeed is permitted to drop below 10 knots, depending on the type of helicopter.