A collective pitch helicopter has blades that can change their angle of attack mid-flight. Although lift can be controlled by changing speed and/or pitch, it is normal to change pitch and to use a throttle curve or governor to keep the head speed more or less constant (more power is required at higher pitch). Collective pitch helicopters can move the blades into a negative pitch angle, which allows them to fly upside down or descend rapidly without loosing head speed and thus cyclic authority.
Collective pitch rotor heads usually use a flybar, with Hiller or Bell-Hiller mixing to the blades. Some larger helicopters now use electronic stabilisation instead of a flybar, resulting in a very simple (and more efficient) rotor head.