A rotorcraft is a heavier-than-air flying machine that uses lift generate by wings that revolve around a mast called rotor blades. Several rotor blades mounted to a single mast is referred to as a rotor. Rotorcraft may also include the use of static lifting surfaces, but the primary distinguishing feature being lift provided by one or more rotors. Rotorcraft include helicopters, autogyros, gyrodynes and tiltrotors. In the United States, the Federal Aviation Administration places helicopters, autogyros (which it calls gyroplanes), and gyrodynes in the category Rotorcraft, and tiltrotors in the category Powered lift.