KAP 140 - NAV - HDG Bug

[TJ1376]

Can someone school me on the KAP 140?

Im locked in on 018 course and in NAV mode with ALT hold mode engaged.

I am getting ready to make a right turn to 025 once I pass the VOR. This is how I want to do it:

about 5 miles from VOR, update HDG bug to correct turn. Airplane should continue to track the 018 radial (im locked in NAV mode)

What really happens:

When I move the HDG bug to 025, the airplane immediately initiates a right turn to 025. I verify I am in NAV mode and I am.

Am I not understanding the correct way to operate the KAP 140? Or is this a bug in how the simulation works?

I am on p3d v2.5 and I have F1 GTN 750 installed but currently not using it (I shift 3 and remove the GTN to go /a only.) I've changed what I do to go to ROL mode, then move the hdg bug, then move the course to the desired course and navigate as I pass over the VOR... But Im curious if I am misunderstanding how to use the KAP140 or if it is simulated incorrectly.

Anyone have real world input?

TJ

[TJ1376]

And from what I've read, apparently I cant do this with the KAP 140, although I dont understand why...

From the Honeywell manual:

NOTE: When NAV is selected, the
autopilot will flash HDG for 5 seconds
to remind the pilot to reset the
HDG bug to the OBS course. Check
the heading displayed on the DG
against the magnetic compass and
reset if necessary

So my assumption is that somehow the HDG bug is slaved even though the KAP140 is following the NAV course. No idea why Honeywell set this up this way, but it appears correct....

TJ

[Tomas Linnet]

yep, I think its correct.
you could co into ROL before passing the VOR, then you'll have the time to set yor heading bug and just go to HDG mode when you want.

[Nick - A2A]

TJ,

Yes, the requirement in the A2A C172 to use the heading bug in NAV mode to tell the autopilot which way to steer is one of the chief ways in which it's more realistic than the default FSX version. I'd suggest a read of this excellent topic to find out more.

In short it's not a bug: the autopilot doesn't have a direct heading signal available to it, so it uses the difference between the heading bug and the lubber line to create a 'heading error' telling it which way to steer to stay on the selected radial. (This means you presumably had the HDG bug set to 018° in order to track the radial successfully...)

In your case, you just need to leave that heading bug on the radial course until after you've switched the KAP 140 to HDG mode.

Cheers,
Nick