N561AMEurocopter France AS350B2 · 2007

On April 15, 2016, about 1955 eastern daylight time, a Eurocopter France AS350B2, N561AM, operated by Air Methods Corporation, was substantially damaged during collision with terrain near Jasper, Georgia. The commercial pilot and three medical flight crewmembers were not injured. Visual meteorological conditions prevailed. The helicopter was operating on a company visual flight rules flight plan from Lanier Park Hospital Heliport (38GA), Gainesville, Georgia, to a helipad at Piedmont Mountainside Hospital, Jasper, Georgia. The helicopter emergency medical service flight was conducted under the provisions of 14 Code of Federal Regulations Part 135.

According to a witness, the helicopter performed a circuit over the hospital prior to approaching the helipad to land. The helicopter began to descend, then about 110 ft above ground level (agl), the helicopter "bobbled up and down" and then it started to "fall quickly toward the ground."

According to the operator and the pilot, the helicopter completed an orbit over the hospital helipad about 800 ft agl prior to beginning a descent for landing. The pilot initiated a downwind approach to the helipad over high tension power lines, about 250 ft agl, and then turned onto the final leg of the approach, which was on a 300° heading. He said the tail rotor became "difficult to control," and the helicopter pitched forward uncommanded, and then began a "rapid descent with forward airspeed."

Believing he "might be in a vortex ring state condition," the pilot reduced the power and initiated a go-around but lacked sufficient altitude to complete the maneuver. The pilot maintained forward airspeed and raised the nose but landed hard, bounced three times, and came to rest upright. The pilot and three medical crew members then exited the helicopter without injury or assistance.

The weather reported at Pickens County Airport (JZP), Jasper, Georgia, about a half-mile northwest of the accident location included wind from 120°at 11 knots, gusting to 16 knots, with 10 miles visibility. The temperature was 18° C, the dew point was -8° C, and the altimeter setting was 30.24 inches of mercury.

Examination of the helicopter revealed substantial damage due to a partial separation of the taiboom. The operator reported, and examination confirmed, that there were no mechanical malfunctions or failures prior to the accident.

According to representatives from Airbus Helicopters, the maximum allowable engine torque setting was for the helicopter was 100 percent continuous. The Vehicle Engine Multifunction Display (VEMD) was reviewed under federal supervision and the data indicated overtorque events at 107 percent for 2 seconds and 113 percent for 1 second.

According to the FAA Rotorcraft Flying Handbook, "vortex ring state" (or "settling with power") describes an aerodynamic condition where a helicopter may be in a vertical (with regard to the air mass) descent with up to maximum engine power applied, and little or no cyclic authority. The term "settling with power" comes from the fact that a helicopter keeps settling, even though full engine power is applied. However, when the helicopter begins to descend vertically, it settles into its own downwash, which greatly enlarges the main rotor blade 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.

A vortex ring state may be entered during any maneuver that places the main rotor in a condition of high upflow and low forward airspeed, including near-vertical descents of at least 300 ft per minute, and a horizontal velocity slower than that for effective translational lift. A fully developed vortex ring state can be "characterized by an unstable condition in which the helicopter experiences uncommanded pitch and roll oscillations."

The handbook also noted that "when recovering from a settling with power condition, the tendency on the part of the pilot is to first try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thus increasing the rate of descent. Recovery is accomplished by increasing forward speed, and/or partially lowering collective pitch." With sufficient altitude, temporary entrance into an autorotation will also enable safe exit from the vortex ring state.