With the operation of the engines so heavily relying on automation, safety is a
great concern. Redundancy is
provided in the form of two or more, separate identical digital channels. Each
channel may provide all engine functions without restriction. FADEC also
monitors a variety of analog, digital and discrete data coming from the engine
subsystems and related aircraft systems, providing for fault
tolerant engine control.
A typical civilian transport aircraft flight may illustrate the function of a
FADEC. The flight crew first enters flight data such as wind conditions,runway length,
or cruise altitude, into the flight
management system (FMS). The FMS
uses this data to calculate power settings for different phases of the flight.
At takeoff, the flight crew advances the throttle to a predetermined setting, or
opts for an auto-throttle takeoff if available. The FADECs now apply the
calculated takeoff thrust setting by sending an electronic signal to the
engines; there is no direct linkage to open fuel flow. This procedure can be
repeated for any other phase of flight.
In flight, small changes in operation are constantly made to maintain
efficiency. Maximum thrust is available for emergency situations if the throttle
is advanced to full, but limitations can’t be exceeded; the flight crew has no
means of manually overriding the FADEC.
FADECs are employed by almost all current generation jet engines, and
increasingly in piston engines for fixed-wing
aircraft and helicopters.
The system replaces both magnetos in piston-engined aircraft, which makes costly
magneto maintenance obsolete and eliminates carburetor heat, mixture controls
and engine priming. Because it controls each engine cylinder independently for
optimum fuel injection and spark timing, the pilot no longer needs to monitor
fuel mixture. More precise mixtures create less engine wear, which reduces
operating costs and increases engine life for the average aircraft. Tests have
also shown significant fuel savings.