This will make flying helicopters a much bigger challenge. Adds to the realism of the game. Might of been one of the reasons why one of the helicopters crashed during the bin laden raid.
The vortex ring state, also known as settling with power, is a dangerous condition that may arise in helicopter flight, when a vortex ring system engulfs the rotor causing severe loss of lift. Essentially, the helicopter descends into its own downwash. When the condition arises, increasing the rotor power merely feeds the vortex motion without generating additional lift.
A helicopter normally encounters this condition when attempting to hover out of ground effect above the hovering ceiling for the aircraft, hovering out of ground effect without maintaining precise altitude control, and while making downwind or steep, powered approaches when the airspeed drops to nearly zero.
The signs of settling with power are a vibration in the main rotor system followed by an increasing sink rate and possibly a decrease of cyclic authority.
In single rotor helicopters, the vortex ring state can be corrected by moving the cyclic control forward, which controls the pitch angle of the rotor blade, slightly pitching nose down, and establishing forward flight. In tandem-rotor helicopters, recovery is accomplished through lateral cyclic or pedal input. The aircraft will fly into "clean air", and will be able to regain lift.