Autopilot and Flightdirector?

[francesco.doenz]

May be not a real A2A forum question, but feeling myself a little bit as a A2A community member I take advantage of the presence of so many knowledgeable people here to ask:
What is in real life the main difference or practical difference between using either the autopilot or the flight director? It's a little bit confusing? Or otherwise asked, is it possible or a reason to use the FD without AP? Or the other way round?
Many thanks in advance!

[speedy70]

Hi Francesco.
I suppose, put in the simplest terms, the FD shows you what to do (according to the FMC or MCP) and you then move the controls to follow the directions. If the autopilot's engaged it will move the controls for you.

As for where and when we use what. The FD is displayed all of the time and the autopilot is only engaged once we've had enough of hand flying or we're required to for an Autoland.

Cheers Chris

[Oracle427]

Another benefit of the FD is that it shows you what the auto pilot is supposed to be doing before being engaged. Much more pleasant than being suprised when the airplane sits of into an unexpected descent low over the ground.

[AKar]

Yes, as answered already, the flight director provides means to display flight guidance system's "commands" to the crew. In typical big plane setup, the autopilot is coupled to the same guidance commands the flight director displays, essentially keeping the command bar(s) centered. There are also other schemes where the flight director and autopilot are not coupled directly together, but the FD commands are calculated independently.

It is, in practice, always possible to use flight director without autopilot. When airliners for instance are hand-flown, that is, from takeoff and most often during the final approach and landing, flight director is typically used as an aid, and the flight director commands should generally be satisfied before engaging the autopilot. Only when the flight guidance commands are to be ignored, the flight director is typically switched off. The use of autopilot without flight director may or may not be possible, depending on the type in question. In typical today's airplanes, the flight director is always on with autopilot, but one could dig for examples where this does not apply.

-Esa

[MatzeH84]

Nearly all classic airliners had these systems seperated, so you could select completely different modes on FD and AP.
With more integrated avionics arriving, the AP will usually be coupled to the FD, in turn the FD, when engaged, will show you what the AP will be doing if engaged.
One could say aircraft of the generation 737CL will be integrated.
In the sim very few addons feature a truly independent AP/FD, in fact the only one coming to my mind is the Coolsky DC9.. Probably the best classic jetliner addon for FS.