Pitch, aircraft control systems

Rotary-Wing Aircraft. Helicopters use the same principles, with two exceptions. The engine in the helicopter is usually hooked directly to the propeller or rotor. It is also hooked in sync with the shaft that turns the rear or tail rotor. The tail rotor is necessary for the directional control of the aircraft. When the collective, the control system that governs lift, is pulled up, it sends directions for the rotor blades to change their pitch and take a larger bite out of the air to lift the machine. Without the tail rotor, torque takes effect, and this causes the aircraft body to rotate in the opposite direction of the rotor blades. The pitch (or amount of bite into the air of the blades) of the tail rotor is controlled by the foot pedals. 

This diagram presents a much-simplified version of the A330 s Electronic Flight Control System, showing its control and protection systems architecture. Because of inadequate design analysis, a particular spike" failure mode in one single air data inertial reference unit (ADIRU) was able to lead to sudden pitch down of the aircraft when in level high-altitude cruise. 

---