Fly-by-wire flight controls are the most advance type of flight controls, where the pilot's actions are inputted into a computer, and the computer then computes the correct signals to send to the control surface actuators (which are hydraulically actuated, for strength). They are lighter that fully powered flight control systems, and also provide the benefit of flight envelope protection, preventing stalls, overspeed, excessive bank angle, excessive G-loading, etc.
These flight envelope protections are categorised into two types, namely:
- Soft protections: Where the system has a limit to protect, but it can be overrided by the pilot. This would be protections which simply make it more difficult to go past the "soft" limit, such as in an A320, where, past 33º angle of bank to the right, the sidestick needs to be held to the right of neutral to maintain that bank angle, otherwise it will return to 33º naturally. Sometimes, these soft protections simply make the pilot push or pull the stick harder to go past the soft limits.
- Hard protection: When hard protections are in place, the control system will not allow these limits to be breached, and the pilot cannot override this. For example, the A320 (in normal law) will not allow the pilot to bank past an angle of 67º, no matter how hard they push the sidestick.
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