A Flight Management System (FMS) is an on-board multi-purpose navigation, performance, and aircraft operations computer designed to provide virtual data and operational harmony between closed and open elements associated with a flight from pre-engine start and take-off, to landing and engine shut-down.
Most modern commercial and business aircraft are equipped with Electronic Flight Instrument System, which replaces conventional systems and flight deck displays.
An FMS comprises four main components:
- The Flight Management Computer (FMC);
- The Automatic Flight Control or Automatic Flight Guidance System (AFCS or AFGS) ;
- The Aircraft Navigation System;
- An Electronic Flight Instrument System (EFIS) or equivalent electromechanical instrumentation.
The FMC is a computer system that uses a large data base to allow routes to be pre-programmed and fed into the system by means of a data loader. The system is constantly updated with aircraft position by reference to available navigation aids. The most appropriate aids are automatically selected during information update.
The AFCS or AFGS receives sensor information from other aircraft systems. Dependent upon whether the aircraft is under Autopilot or manual control, AFCS mode selections made by the crew will either automatically move and control the aircraft flight control surfaces or display Flight Director commands for the pilot to follow to achieve the desired status.
The Navigation System is an integrated package which calculates continuously the aircraft position. It may include Inertial Reference System (IRS) and Global Positioning System (GPS) (GPS) inputs in addition to receivers for ground based aids. In the case of an EFIS, the display of these navigational inputs is predicated on the Attitude and Heading Reference System(AHRS).
Display of aircraft status is provided on either EFIS or conventiomal instrumentation and is where the effect of FMS aircraft control is principally visible.