Settling with power is an aerodynamic phenomenon from which helicopters suffer because they pull air down through a rotor system.
At high gross weights, high density altitudes and high power settings (because they're really heavy), helicopters can begin to "settle in their own downwash." They begin to develop higher and higher rates of descent until the rate of descent is so fast that the air is actually flowing UP through the rotor system, rather than from top to bottom. This causes a vortex ring state around the rotor blades, rendering them pretty much useless.
Have you ever seen the jet wash from an airplane? Those "air circles" that form as a plane lands and the tires create smoke? When helicopters get slow enough -- between 16 and 24 knots, or below "effective translational lift" -- they begin to actually operate in those vortices. If we sink too fast, all that rotorwash is basically shoved back through the rotor system and it screws up the airflow, causing you to develop faster and faster rates of descent. A pilot can correct this problem by simply moving out of the air column, either forward or laterally. But pushing forward on the controls is probably the last thing someone who's trying to stop would do.
That make any sense?
As for the 160th comment, those forkers are always balling up aircraft and killing people. They think their shirt doesn't stink. Well, guess what, assholes. It does.