Definition
A cockpit panel, typically consisting of a small screen and a keypad, used by the flight crew to enter data into and read information from onboard avionics systems such as the Flight Management System (FMS), navigation computers, or maintenance computers. The CDU is the primary interface for programming flight plans, performance data, and system parameters.
Plain English
A small screen with buttons in the cockpit that the pilots use to type information into the aircraft's computers and to see what those computers are telling them.
Context Anchor
Seen in cockpit avionics, especially when entering route, navigation, or aircraft performance information before and during flight.
Derivation
The name describes its two functions: it controls (sends commands and data into) the aircraft systems, and it displays (shows back) the resulting information. Putting both jobs in one box gives you a Control Display Unit.
Why Pilots Care
The CDU is how the crew programs the flight. An incorrect entry — wrong waypoint, wrong weight, wrong runway — directly affects navigation, fuel planning, and takeoff performance. Cross-checking CDU entries is a core flight-deck discipline.
Analogy
It is like a keyboard and screen for a specific aircraft computer: the computer does the work, but the CDU is how the pilot gives it information and reads the result.
Intuition Check
Do not think of the CDU as the main computer itself. It is usually the control-and-display interface used to communicate with another aircraft system.
Example Sentence 1
Before pushback, the first officer entered the flight plan and weights into the CDU.
Example Sentence 2
The CDU screen displayed the current fuel range and next waypoint.