Flight Planning: The FMS provides a computerized flight planning aid to the pilot, primarily through the Command/Display Unit (CDU). This function allows for the creation, modification, and management of the flight plan.

Navigation and Guidance: The FMS combines data from various navigation sources (such as INS, GPS, navaids) to derive the best estimate of the aircraft's position and velocity. It then provides both lateral (LNAV) and vertical (VNAV) guidance to the flight control systems, such as the autopilot or flight director.

Optimization and Performance Prediction: The FMS optimizes the flight plan by selecting the appropriate speed, altitude, and engine power settings during all phases of flight. It integrates knowledge about aircraft type and weight, fuel weight, engine type, performance characteristics, and other relevant factors.

Learn: Avionics Part II