Flight Management System (FMS) – The Aircraft’s Brain!

Apart from the first officer’s and captain’s human brains, that manage to fly modern aeroplanes safely through the world’s skies, another brain has appeared on board of today’s flying machines since the early 1980s. A brain of technical nature! In today’s article, I want to discuss the flight management system (FMS).



The flight management system is capable of quite a number of useful things. For instance, the FMS helps the flight deck crew by calculating route- climbing, as well as descending-profiles. In favor of a better overall-view for the pilots, the FMS displays this information visually on the so-called “multi-function-displays (MFDs)” on the flight deck. This can be, for example, the route to be flown, including the airways and waypoints.

The flight management system of an Airbus A320-200

The Flight Management System: An Allrounder!

The best thing about the FMS is, however, that it does not only display the information. It is coupled with the autopilot! With the help of the FMS, the autopilot can hence automatically fly the precalculated lateral and vertical flight profile. Another great help for this is the aircraft’s auto-thrust system. It autonomously adjusts the thrust level of the engines.

To determine the aircraft’s position, the flight management system makes use of the “Inertial Navigation System“. In simple terms, the INS has the main advantage when compared to classic means of navigation, that it does not need a reference point. It determines the current geographical position with the help of rate-gyroscopes accelerometers.

• The INS updates this information continuosly throughout the flight. This happens with the help of a GPS or sorrounding VORs and NDBs.
• VOR is short for “VHF omni directional radio range”. VORs are fixed radio beacons that help aircrafts to navigate by transmitting radio signals.
• An NDB is a “non-directional (radio) beacon (NDB)“, which is also a navigational aid. As the name tells, it does not contain inherent directional information, in contrast to a VOR. It emits radio signals in all directions.

The Control Display Unit (CDU)

Okay, the features of the flight management system sound great. But how do pilots feed the FMS with information? This is where the so called “control display unit (CDU)” steps into the game. You can imagine this CDU as some kind of a conventional small computer with an alphanummerical keyboard attached to it, as well as a tiny display.

Prior to every flight, the FMS is fed with all relevant data via the CDU. This data includes the zero fuel weight (ZFW) of the plane, as well as the fuel on board, the number of passengers and the loaded freight’s mass. More essential information the FMS requires are the planned route and cruising altitude, as well as the cruising speed aimed for.

A first officer, typing into the control display unit of his Airbus A320

Of course, this data can always be updated during the flight. This is useful in particular, for instance, to fly holdings or to change the route. In almost all modern planes, the CDU is located between the two pilot’s seats. In really new commercial aeroplanes, CDUs even include touch displays!

More Aviation Knowledge!

You want to learn more about the complex world of aviation and flying? Feel free to browse through my “Aviation 101” section. Also, you might want to read my article about the instrument landing system!

I do hope that you have enjoyed this article about the flight management system. More aviation know-how will come every week on pilotstories. In the meantime, feel free to subscribe my email newsletter and to follow me on Facebook and Instagram. My free aircraft wallpapers are available here!