Flight management system
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A flight management system or FMS is a computerized avionics component found on most commercial and business aircraft to assist pilots in navigation, flight planning, and aircraft control functions.
It is considered to be composed of four major components: FMC (Flight Management Computer), AFS (Auto Flight System), Navigation System including IRS (Inertial Reference System) and GPS, and EFIS (Electronic Flight Instrument System).
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[edit] Flight Management Computer
The FMC is taken as the core of FMS, which works as a head of the whole system. Its primary function is to:
- Give out real-time lateral navigation information by showing the route programmed by the pilots, as well as other pertinent information from the database, such as standard departure and arrival procedures. This information combined with the location of the aircraft creates a moving map display.
- Calculate performance data and predicted vertical profile. Based on weight of the aircraft, Cost Index and Cruise Altitude, preferably with predicted wind, FMC calculate a most fuel efficient vertical path that AFS would follow if AFS is engaged and both of VNAV and LNAV are engaged.
[edit] Auto Flight System
If FMC is taken as the "head" of the system who does the calculation and gives out command, AFS is the system who accomplishes it. AFS is composed of AFDS (A/P-Autopilot-F/D-(Flight Director) and A/T(Autothrottle) if the aircraft is equipped with A/T. It is the one who flies the airplane with one hand on the control wheel (when A/P is engaged), and the other hand on the throttle (when A/T is engaged). Only when the mode LNAV and VNAV, or LNAV, or VNAV is engaged, AFS would totally or partly follow the flight path FMC commands.
[edit] Navigation system
It is mainly composed of IRS (Inertial Reference System) or AHRS (Attitude Heading and Reference System) and GPS (Global Positioning System), as well as existing physical navaids such as VOR-DME. GPS is so far the most precise system to locate the airplane's position. What IRS and AHRS can do and GPS cannot do is that IRS gives out raw information such as attitude and heading of the airplane which is crucial to flight. The navigation system send navigation information to FMC to calculate, to AFS to control the aircraft, and to EFIS system to display. Little action is needed from the pilots during the whole phases of flight.
[edit] EFIS
EFIS, as a display system displays flight information including command from FMC and real-time information such as attitude, heading, position, planned route and flight track, etc. It is composed of EADI (Electronic Attitude Display Indicator) and EHSI (Electronic Horizontal Status Indicator), or on some aircraft PFD (Primary Flight Display) and ND (Navigation Display). Either of them displays lateral or vertical flight information.
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