What is a Flight Management System (FMS) and what are its functions?

The FMS is an integrated computer system that assists pilots in navigation, flight planning, and aircraft control. Key functions include: Navigation database management (airways, waypoints, procedures), Flight plan entry and modification, Performance calculations (fuel, time, speeds, optimal altitude), Lateral navigation (LNAV - horizontal guidance), Vertical navigation (VNAV - altitude, speed profile), Autopilot and autothrottle coupling, and Display management. The FMS integrates inputs from multiple sensors (GPS, INS, DME, VOR) for optimal position estimate. CDU (Control Display Unit) or touchscreen provides pilot interface. Modern FMS enables precision RNAV approaches and efficient flight profiles.