A FBW aircraft can be lighter than a similar design with conventional controls.
Partly due to the lower overall weight of the system components; and partly
because the natural aerodynamic stability of the aircraft can be relaxed,
slightly for a transport aircraft and more for a maneuverable fighter, which
means that the stability surfaces that are part of the aircraft structure can
therefore be made smaller. These include the vertical and horizontal stabilizers
(fin and tailplane) that are (normally) at the rear of the fuselage.
If these structures can be reduced in size, airframe weight is reduced. The
advantages of FBW controls were first exploited by the military and then in the
commercial airline market. The Airbus series of airliners used full-authority
FBW controls beginning with their A320 series, see A320
flight control (though some limited
FBW functions existed on A310). Boeing
followed with their 777 and later designs.
Electronic fly-by-wire systems can respond flexibly to changing aerodynamic
conditions, by tailoring flight
control surface movements so that
aircraft response to control inputs is appropriate to flight conditions.
Electronic systems require less maintenance, whereas mechanical and hydraulic
systems require lubrication, tension adjustments, leak checks, fluid changes,
etc. Furthermore, putting circuitry between pilot and aircraft can enhance
safety; for example the control system can try to prevent a stall, or it can
stop the pilot from over stressing the airframe.
The main concern with fly-by-wire systems is reliability. While traditional
mechanical or hydraulic control systems usually fail gradually, the loss of all
flight control computers could immediately render 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 such as the latter is not
desirable and modern FBW aircraft normally avoid it by having more independent
FBW channels, thereby reducing the possibility of overall failure to minuscule
levels that are acceptable to the independent regulatory and safety authority
responsible for aircraft design, testing and certification before operational