What is FMCS?

FMCS most likely refers to a Flight Management Computer System. This is a core component of a modern airliner's avionics. It automates a wide variety of in-flight tasks, reducing the workload on the flight crew. Primary functions include flight planning, performance calculation, navigation, and guidance. It integrates and displays information from various sensors, such as GPS, inertial reference systems, and radio navigation aids. The FMCS optimizes the flight path for fuel efficiency and provides autopilot control signals.