Batesville, TX, USA
N748BP
Robinson R44
The 1,469-hour pilot and three passengers had departed a private ranch to conduct a deer survey. Approximately 30 minutes after takeoff the pilot was making a left turn when they spotted a deer to the right of the helicopter. The pilot turned slowly to the right and the rpm horn sounded. The pilot lowered the collective and rolled on throttle while turning the helicopter into the wind. The helicopter encountered a settling with power condition and it continued to sink. The pilot then flew the helicopter to the ground in a controlled crash.
On September 21, 2005, approximately 1730 central daylight time, a Robinson R44 single-engine helicopter, N748BP, sustained substantial damage when it impacted terrain while maneuvering near Batesville, Texas. The commercial helicopter pilot and three passengers 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 Batesville, Texas, approximately 1700. The 1,469-hour pilot of N748BP reported in the Pilot/Operator Aircraft Accident Report (NTSB 6120.1/2) that he and three passengers had departed a private ranch to conduct a deer survey. Approximately 30 minutes after takeoff the pilot was making a left turn when they spotted a deer to the right of the helicopter. The pilot turned "slowly" to the right and the rpm horn sounded. The pilot lowered the collective and rolled on throttle while turning the helicopter into the wind. The helicopter continued to sink as the pilot attempted to recover main rotor rpm. The pilot then flew the helicopter to the ground in a "controlled crash." The helicopter came to rest against a tree with structural damage to the fuselage. There was additional damage to the main and tail rotor blades and the landing gear skids. 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 aerodynamic 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." The pilot stated in the NTSB Form 6120.1/2 under the section; Recommendation (How This Accident Could Have Been Prevented): "Maintain higher altitude in turns and don't turn into downwash and enter into settling with power."
The pilot's failure to maintain rotor rpm and his subsequent encounter with settling with power.
Source: NTSB Aviation Accident Database
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