Editing Fly-by-wire (section)

== Safety and redundancy ==

While traditional mechanical or hydraulic control systems usually fail gradually, the loss of all flight control computers immediately renders the aircraft uncontrollable. For this reason, most fly-by-wire systems incorporate either redundant computers (triplex, quadruplex etc.), some kind of mechanical or hydraulic backup or a combination of both. A "mixed" control system with mechanical backup feedbacks any rudder elevation directly to the pilot and therefore makes closed loop (feedback) systems senseless.<ref name=suth/>

Aircraft systems may be quadruplexed (four independent channels) to prevent loss of signals in the case of failure of one or even two channels. High performance aircraft that have fly-by-wire controls (also called CCVs or Control-Configured Vehicles) may be deliberately designed to have low or even negative stability in some flight regimes {{ndash}} rapid-reacting CCV controls can electronically stabilize the lack of natural stability.<ref name=unstable>{{cite web| url = https://jagger.berkeley.edu/~pack/me234/GSBode.pdf| title = Respect the unstable – Berkeley Center for Control and Identification| access-date = 3 February 2018| archive-date = 15 July 2010| archive-url = https://web.archive.org/web/20100715204904/http://jagger.berkeley.edu/~pack/me234/GSBode.pdf| url-status = dead}}</ref>

Pre-flight safety checks of a fly-by-wire system are often performed using [[built-in test equipment]] (BITE). A number of control movement steps can be automatically performed, reducing workload of the [[Aviator|pilot]] or [[groundcrew]] and speeding up flight-checks.{{Citation needed|date=June 2010}}

Some aircraft, the [[Panavia Tornado]] for example, retain a very basic hydro-mechanical backup system for limited flight control capability on losing electrical power; in the case of the Tornado this allows rudimentary control of the [[stabilator]]s only for pitch and roll axis movements.<ref>{{Cite book|title=The Birth of a Tornado|publisher=Royal Air Force Historical Society|year=2002|pages=41–43}}</ref>