Flight control modes

A flight control mode or flight control law is a computer software algorithm that transforms the movement of the yoke or joystick, made by an aircraft pilot, into movements of the aircraft control surfaces. The control surface movements depend on which of several modes the flight computer is in. In aircraft in which the flight control system is fly-by-wire, the movements the pilot makes to the yoke or joystick in the cockpit, to control the flight, are converted to electronic signals, which are transmitted to the flight control computers that determine how to move each control surface to provide the aircraft movement the pilot ordered.

A reduction of electronic flight control can be caused by the failure of a computational device, such as the flight control computer or an information providing device, such as the Air Data Inertial Reference Unit (ADIRU).

Electronic flight control systems (EFCS) also provide augmentation in normal flight, such as increased protection of the aircraft from overstress or providing a more comfortable flight for passengers by recognizing and correcting for turbulence and providing yaw damping.

Two aircraft manufacturers produce commercial passenger aircraft with primary flight computers that can perform under different flight control modes. The most well-known is the system of normal, alternate, direct laws and mechanical alternate control laws of the Airbus A320-A380. The other is Boeing's fly-by-wire system, used in the Boeing 777, Boeing 787 Dreamliner and Boeing 747-8.

These newer aircraft use electronic control systems to increase safety and performance while saving aircraft weight. These electronic systems are lighter than the old mechanical systems and can also protect the aircraft from overstress situations, allowing designers to reduce over-engineered components, which further reduces the aircraft's weight.