What is the function of the CDU/MCDU in FMS operations?

• A. User interface for route planning, performance inputs, wind data, and flight plan management; used to load and modify data
• B. Primary engine control unit
• C. Displaying cabin announcements
• D. Handling autopilot disconnects

Answer: (A)

The CDU/MCDU is the primary user interface to the Flight Management System. It’s how pilots enter and edit the flight plan, performance data, wind and temperature data, and other inputs the FMS uses to compute the optimal route and guidance. Through the CDU/MCDU you load, modify, and manage the route, add performance parameters (like speeds, altitudes, and costs), and refresh navigation data as needed. The FMS processes these inputs to generate leg-by-leg navigation guidance and fuel-efficient trajectories that the autopilot follows.

This isn’t the engine control unit or a cabin display device. It doesn’t control engines, and it isn’t used to display cabin announcements or handle autopilot disconnects. Those functions are performed by other systems or controls on the aircraft.