Definition
The control/display unit is the cockpit interface a pilot uses to communicate with the flight management system (FMS). It consists of a small screen and a keypad, typically mounted on the center pedestal, through which the pilot enters flight plan data, performance information, and navigation requests, and views the system's responses.
Plain English
The CDU is the keyboard-and-screen panel the pilot uses to talk to the airplane's flight computer. You type things in, the computer shows answers back.
Context Anchor
Seen when learning how an FMS is operated in the cockpit, especially when entering or checking route and performance information before or during a flight.
Derivation
The name describes its two functions: it is the unit that lets the pilot control the FMS (through the keypad) and display its information (on the screen). Putting both functions in one box gives the pilot a single place to interact with the system.
Why Pilots Care
The CDU is the primary way pilots program and modify the FMS in flight. Entries made here drive the autopilot, navigation displays, and fuel/performance calculations, so accuracy matters and CDU skill is a core part of operating modern aircraft.
Analogy
Think of the FMS as the computer and the CDU as the keyboard and screen used to work with it.
Intuition Check
Do not treat the CDU as the whole FMS. The CDU is the pilot’s control and display interface; the FMS is the system behind it that processes the information.
Example Sentence 1
Before pushback, the first officer entered the route into the CDU and verified each waypoint against the flight plan.
Example Sentence 2
During cruise the first officer reviewed the arrival routing on the CDU display.