What is the primary purpose of the CDU/MCDU in FMS operations (flight planning and data management)?

• A. Load and modify route, performance data, wind data, and flight plan management
• B. Manage hydraulic systems
• C. Control cabin temperature
• D. Display weather radar on ND

Answer: (A)

The CDU/MCDU is the primary interface to the Flight Management System for loading and editing the flight plan and related data. Through it you load and modify the route—origin, destination, and the sequence of waypoints, along with any altitude and speed constraints. You also input and adjust performance data, such as climb/descent speeds and thrust settings, plus wind data, which the FMS uses to calculate the most efficient path and accurate fuel and timing estimates. In addition, it handles overall flight plan management—updating legs, constraints, and re-planning as needed—so the FMS can recompute the lateral and vertical navigation guidance accordingly. This is all about data management and planning within the FMS.

The other options don't pertain to the CDU/MCDU’s role: hydraulics, cabin temperature control, and weather radar display are handled by separate systems and controls outside the FMS input interface.