Bandera, TX, USA
N422SH
Robinson R22
The 2,216-hour pilot refueled at a private ranch and departed with a passenger to "begin a process of herding some exotic animals across an earthen dam to an open area for capture." One particular trophy exotic that they were trying to capture began to swim in a creek below, and "it was obvious that the animal was struggling to cross." The pilot then began to hover beside the animal to herd it out of the water and towards the bank. At this point, "the aircraft began to settle with power at a height of approximately six feet above the water." The pilot "applied forward cyclic and right pedal, along with a lower collective setting. The skid gear then settled into the water with forward motion, and the main rotors contacted the water." The helicopter sank in approximately six feet of water.
On April 27, 2005, approximately 0831 central daylight time, a Robinson R22 single engine helicopter, N422SH, sustained substantial damage when it impacted water while hovering near Bandera, Texas. The commercial helicopter pilot and his passenger were not injured. Visual meteorological conditions prevailed and a flight plan was not filed for the animal herding flight, which was conducted under the provisions of 14 Code of Federal Regulations Part 91. The local flight originated from a private ranch near Bandera, Texas, approximately 0820. In a written statement, the 2,216-hour pilot reported that after refueling at a private ranch, he and a passenger departed and "began a process of herding some exotic animals across an earthen dam to an open area for capture." One particular trophy exotic that they were trying to capture began to swim in a creek below, and "it was obvious that the animal was struggling to cross." The pilot then began to hover beside the animal to herd it out of the water and towards the bank. At this point, "the aircraft began to settle with power at a height of approximately six feet above the water." The pilot "applied forward cyclic and right pedal, along with a lower collective setting. The skid gear then settled into the water with forward motion, and the main rotors contacted the water." The helicopter sank in approximately six feet of water. A review of photographs taken after the accident revealed structural damage to the main rotor blades and the fuselage. According to the Federal Aviation Administration (FAA) Rotorcraft Flying Handbook, pages 11-5 to 11-7, Vortex Ring State (Settling with Power), "Vortex ring state describes an areodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little, or no cyclic authority. The term 'settling with power' comes from the fact that the helicopter keeps settling even though full engine power is applied. In a normal out-of-ground effect-hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor system and rejoining the air entering the rotor from the top. 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 accelerating the air in a doughnut pattern around the rotor. In addition, the helicopter may descend at a rate that exceeds the normal downward induced-flow rate of the inner blade sections. As a result, the airflow of the inner blade sections is upward relative to the disc. This produces a secondary vortex ring in addition to the normal tip-vortices. The secondary vortex ring is generated about the point on the blade where the airfoil changes from up to down. The result is an unsteady turbulent flow over a large area of the disc. Rotor efficiency is lost even though power is still being supplied from the engine." At 0745, the automated weather observing system at the Kerrville Municipal Airport (ERV), located approximately 20 nautical miles north of the accident site, reported no wind, scattered clouds at 12,000 feet, 10 statute miles visibility, temperature 52 degrees Fahrenheit, dew point 45 degrees Fahrenheit, and a barometric pressure setting of 30.08 inches of Mercury.
The pilot's loss of control while hovering after encountering settling with power.
Source: NTSB Aviation Accident Database
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