The overall objective of the flight control laws integrated into a fly-by-wire system is to improve the natural qualities of flight of the aircraft, particularly in the fields of stability, control and protection domain of flight. In a fly-by-wire system, teams can easily process the airspeed and inertial information, and any information that describes the condition of the aircraft. The inputs of the sticks are transformed by teams in the pilot control objectives, which are compared with the actual status of the aircraft measured by the inertial sensors and anemometer. Thus, with respect to the longitudinal control is concerned, the position of side stick demands results in vertical load factor, while the lateral control via roll rate is achieved, and side slip bank angle.
The increased stability provided by the laws flight control aircraft flying qualities enhances and contributes to the safety of the aircraft. The aircraft is stable in case of disturbances such as gusts or engine failures (asymmetric thrust). The control of the aircraft through the objectives, significantly reduces the workload of the crew, the fly-by-wire system acts as the inner loop of an autopilot system, while the pilot represents the outer loop by management. Finally, protection prohibiting potentially dangerous excursions outside the normal flight envelope can be integrated into the system. The main advantage of such protections is to allow the pilot to react quickly without hesitation, because he knows that this action will not result in a critical situation.
Control laws implemented in the computers of the flight control system, have full authority and must be made on the basis of consolidated information from at least two independent sources. Therefore, the availability of the laws of the feedback control using the plane (called normal laws), are closely related to the availability of the sensors. The fly-by-wire Airbus aircraft, information systems use three Inertial Reference Units and Data Aire (ADIRUs) as well as accelerometers and gyroscopes specific. Furthermore, in the case of normal longitudinal law, analytical redundancy is used to validate information pitch rate when provided by a single inertial reference unit. The load factor is calculated through information and pitch rate is compared to the accelerometer measurements available to validate the IRS data. After a double or triple failure, when it becomes impossible to compare data from independent sources, normal control laws are reconfigured in the laws of the direct type, where the deviation of the control surface is proportional to the sidestick input. To increase the disymetry, more sophisticated feedback control laws of the aircraft (the normal laws) are integrated in a kind of computer, while the other type of computer incorporates only direct laws.