In flight, what is the relationship between FMS auto-speed management and autothrust?

• A. The FMS defines target speeds; Autothrust adjusts engine thrust to maintain those speeds.
• B. Autothrust defines target speeds; FMS implements them.
• C. The FMS and autothrust operate independently with no interaction.
• D. Autothrust provides only advisory guidance and does not automatically control thrust.

Answer: (A)

In flight, auto-speed management from the FMS sets the speed targets that the aircraft should follow. The FMS calculates constraints along the route (target Mach or indicated airspeed at waypoints, plus any climb or descent speeds) and provides these as the desired speeds. Autothrust then automatically modulates engine thrust to achieve and maintain those targets. It continuously compares the actual airspeed to the target and adjusts thrust to minimize the speed error, delivering the commanded performance without manual thrust input. While you can override targets by selecting a different speed, in normal managed-speed operation the FMS defines the targets and autothrust implements them.