Plain English Meaning

What the FMS actually does: it takes the route the pilot enters, figures out where the aircraft is, works out the best path to fly, and tells the autopilot and the cockpit screens how to follow it.

Full Definition

The role performed by a Flight Management System (FMS): an integrated avionics computer that combines navigation, performance, and guidance data to manage an aircraft's flight path. It accepts pilot inputs (route, waypoints, performance parameters), draws position information from multiple navigation sources (GPS, VOR/DME, IRS), calculates the optimal lateral and vertical path, and issues steering and performance to the autopilot, , and cockpit displays.