How do I use the Honeywell FMC to fly like an autopilot in FSX?

Using the “Honeywell FMC” as an autopilot in FSX

What trips a lot of folks up here is that, in plain FSX, an FMC (even one that looks like a Honeywell unit) doesn’t actually “fly the airplane” by itself. The FMC is the navigation/flight planning computer. The thing that turns that plan into turns/climbs/descents is the aircraft’s autopilot/flight director following a lateral/vertical mode (LNAV/VNAV, NAV, etc.).

So the real answer depends 100% on which aircraft/add-on you’re using, because FSX doesn’t ship with a full Honeywell-style FMC that drives LNAV/VNAV like a study-level add-on does.

General workflow (what you’re trying to do)
If the aircraft is one that supports it, the steps are usually along these lines:

1. Build/activate a route in the FMC (origin/destination, SID/STAR if available, legs, etc.).
2. Make sure the aircraft’s navigation source is set to the FMC/GPS (not raw VOR/LOC), if the panel has that option.
3. Engage the autopilot and select the appropriate modes:
   • Lateral: something like NAV / LNAV / FMS (name depends on the airplane).
   • Vertical: something like VNAV, or a managed climb/descent mode; otherwise you’ll use VS/FLCH/ALT HOLD manually.
4. Verify the annunciations (FMA/mode display) actually show it’s tracking the FMC and not just holding heading.

Important reality check
If this is the default FSX GPS-style setup (or a simple “FMC-looking” gauge), it may only be for display/flight plan entry and will not provide true LNAV/VNAV guidance to the autopilot. In that case, you’d typically use:

• HDG mode to steer, and/or
• NAV mode to follow a VOR/LOC, and/or
• GPS/NAV switch (if the aircraft has one) to let NAV mode follow the GPS flight plan instead of VOR.

A couple quick questions so I can give you the exact button-pushes

1. Which aircraft are you flying (default 737/747, or an add-on—what name)?
2. Where are you seeing the “Honeywell FMC” (2D popup, VC pedestal, etc.)—is it part of an add-on panel?
3. When you press your autopilot NAV mode, does it track anything at all (VOR, GPS), or does it just stay in HDG?

Once I know the aircraft and whether that FMC is actually connected to an FMS/autopilot system, I can walk you through the exact steps/modes to make it fly the route.