What is a primary function of the FMS?

• A. In-flight management of the flight plan
• B. Display of weather radar data
• C. Provision of autopilot control
• D. Air traffic collision avoidance

Answer: (A)

The Flight Management System is primarily used to manage and optimize the aircraft’s flight plan while airborne. It stores the planned route, computes leg distances, times, and fuel burn, and handles navigation guidance by determining the best lateral path (LNAV) and vertical profile (VNAV) to meet constraints like speed, altitude, and ATC instructions. It continually updates the plan in response to wind, weight changes, weather, or airspace restrictions, and it feeds guidance information to the flight guidance/autopilot system so the aircraft can follow the chosen route efficiently. Weather radar displays and collision avoidance are separate systems, not the primary function of the FMS, which is why the in-flight management of the flight plan is the best choice.