Hello friends, I have few noob question about real life ATC. First, before RC I used to fly with FMC, using SID and STARS. After a few flight with RC, I noticed I never use FMC, because ATC gives all headings. So just wondering, how this work in real life, when pilots use FMC, and if ATC saying everything to you, why you need FMC ? Thanks.

Well, in the real world, ATC does not tell you everything throughout your flight. (In RC there is an option called IFR training and if enabled it will not show you the direction to your next checkpoint.) For departure and arrival you may or may not get vectors but also there are SIDs and STARs plus approaches in its database.ATC expects you to fly your filed flight plan and other than altitude changes or corrections enroute you will not hear much from them unless you degiate from your filed plan. The FMC provides both heading and altitude guidance plus departure and arrival guidance in addition to fuel planning and monitoring and other assistance regarding performance. It can be coupled to the autopilot/flight director when its guidance agrees with ATC.Depending on the airport type ATC might set you up for the Initial Approach Fix and clear you to it for completion on your own navigation. This includes non-controlled airports. An FMC can assist in this offering navigational guidance.The question you pose might be reversed such as why do you need ATC if you have an FMC. The answer is aircraft separation and guidance when needed for safe flight and orderly enroute and airport traffic operation.A GPS also has many of the FMC navigational features but none of the fuel planning and performance features. It is limited to horizontal navigation only. Depending on the aircraft model the FMC can use its GPS receivers as well integrating that information into its navigation system.I should add that my first flights with RC were with general aviation aircraft not equipped with an FMC and only added a good GPS instrument later. I controlled altitude manually or through the autopilot. Without the GPS I just used VOR navigation using dual VOR receivers for getting to intersection waypoints meeting waypoints I had in the flight plan. Good training :) . I should add that in the real world back in the mid 1970's that how I flew many routes with GA aircraft VFR and also for training in IFR. You can fly IFR with just the minimal instrument set required for navigation.

Ronzie thanks a lot mate, noone could explain this better. :(