The primary flight controls of the Tornado are a fly-by-wire hybrid, consisting of an analogue Command and Stability Augmentation System (CSAS) connected to a digital Autopilot & Flight Director System (AFDS); in addition a level of mechanical reversion capacity was retained to safeguard against potential failure. To enhance pilot awareness, artificial feel was built into the flight controls, such as the centrally located stick; because of the Tornado's variable wings enabling the aircraft to drastically alter its flight envelope, the artificial responses adjust automatically to wing profile changes and other changes to flight attitude. As a large variety of munitions and stores can be outfitted, the resulting changes to the aircraft's flight dynamics are routinely compensated for by the flight stability system.
The Command Stability Augmentation System (CSAS) is by its very nature one of the most complex systems on Tornado. Hardly detectable in the cockpit, the CSAS keeps the ride comfortable at all speeds and altitudes, and makes the aircraft controllable throughout the flight envelope. It is a "fly-by-wire" system with autostabilisation, the pilot’s control demands being signalled and augmented electrically to maintain good handling qualities over the wide flight envelope. In the pitch axis, the "fly-by-wire" system has mechanical reversion.
The system is triplicated and includes triplex computing, triplex rate gyros, triplex position sensors and a triplex accelerometer, with quadruplex outputs driving quadruplex electrohydraulic actuators. These "fly-by-wire" actuators were originally designed by Marconi-Elliott Avionic Systems Limited and have now been integrated by Fairey Hydraulic into the aircraft’s main hydraulic power control units.
The CSAS electronics is packaged in two units, the pitch computing circuitry being housed in a single computer and the roll, yaw and spoiler circuitry in a similar computer.
The system uses very high-precision analogue circuitry to provide accurately- matched control lanes, and a unique voter monitor design which reduces transient effects, due to system failures, to a low level and is so designed also that nuisance warnings are rare.
Marconi-Elliott Avionic Systems Limited has design leadership on the CSAS programme, but shared the production with Bodenseewerk Geratetechnik.
The system was designed to Specification SP-P-41600.
The Command Stability Augmentation System comprises the following line replaceable units,
1 Rudder pedal position transmitter Between front rudder pedals.
2 CSAS Power Distribution Unit Right hand forward avionic compartment.
3 CSAS Control Unit Front Cockpit - left hand console.
4 Pitch Computer Right hand rear avionic compartment.
5 Lateral Computer Right hand rear avionic compartment.
6 Roll Position Transmitter Zone 19. Roll crate.
7 Pitch Position Transmitter Zone 19. Pitch crate.
8 Yaw Rate Gyro Zone 22. Right hand under-carriage bay.
9 Roll Rate Gyro Zone 21. Left hand under-carriage bay.
10 Pitch Rate Gyro Zone 21. Left hand under-carriage bay.