What are the difference between FMC, FMS and MCDU and what do they do?

Do airliners have all of them or just 1 or 2 of them?

Do pilots learn how to program them/it?

FMC = Flight Management Computer

FMS = Flight Management System

MCDU = Multi-Function Control and Display Unit

  • 2
    $\begingroup$ Hi and welcome. Please see the linked post and see if it answers your first questions. Note that here it is better to limit each post to one question. $\endgroup$
    – user14897
    May 5, 2019 at 12:09

1 Answer 1


With specifics depending on aircraft, generally the following applies:

FMC - Flight Management Computer

FMS - Flight Management System (consisting e.g. of two FMCs)

MCDU - Multi-Purpose Control and Display Unit (2 or 3 installed on the aircraft, the screen and keypad unit by which the crew interfaces with the FMS)

Airliners have all of the functions provided by the boxes above, although depending on setup sometimes some of the computers are called differently or are unified. E.g. on Boeings, it’s called a CDU not MCDU, and some retrofit older airliners have an FMCDU which is an MCDU with a built-in FMC.

Of course crew learn how to operate these systems.

  • $\begingroup$ I used to call the RC FMS the "TV Remote From Hell" insofar as you had to master a long list of non-intuitive arbitrary commands, made worse by the key bounce problems that caused constant double entries on key strokes. There are lots of RJs with single FMS. If it goes out, it's back to old school dial twiddling. $\endgroup$
    – John K
    May 5, 2019 at 13:35