IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM

"VNAV Suspended"

Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=2758
Printed Date: 20 Jun 2025 at 6:20pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com

Topic: "VNAV Suspended"

Posted By: frankbell
Subject: "VNAV Suspended"
Date Posted: 20 Jun 2025 at 10:18am

IFD 540: I have just started having a problem with intercepting an RNAV approach, specifically the vertical nav (glideslope). Using a Garmin 500 autopilot. When I am close to the final approach course, I'm getting a "VNAV Suspended" message, and the autopilot does not capture the decent path. Software level 10.3.1.2.

This is a new problem... it's worked just fine in the past. Can't think of any changes which might have made any difference.

Replies:

Posted By: dmtidler
Date Posted: 20 Jun 2025 at 10:44am

According to the IFD540 PG, "VNAV Suspended" (and "VNAV Terminated") advisory messages only relate to Enroute VNAV operations being suspended or terminated due to various conditions. This should not affect RNAV GPS approach vertical guidance.

I have a similar setup with a couple of G5's and a GFC500 autopilot. The autopilot will not follow the IFD540 Enroute VNAV vertical guidance; however, will capture and follow RNAV GPS approach vertical guidance when the GFC500 APR mode is armed/active.

BTW - in my experience, it is normal for the "VNAV Terminated" advisory message to appear when the IFD540 transitions from enroute VNAV to approach vertical guidance if I've been following the enroute VNAV guidance.

Posted By: frankbell
Date Posted: 20 Jun 2025 at 11:42am

"should not affect RNAV GPS approach vertical guidance...", but apparently it does. Not using enroute VNAV.

Posted By: dmtidler
Date Posted: 20 Jun 2025 at 12:38pm

Keep in mind, if Enroute VNAV is enabled on your IFD Main System Config page and your active approach has any stepdown fixes outside of the FAF, then until passing the last stepdown point or the FAF becomes the active waypoint, Enroute VNAV is being used.

It appears by your description that Enroute VNAV is enabled on your IFD's Main System Config page because the "VNAV Suspended" advisory would not appear if Enroute VNAV was disabled.

Posted By: frankbell
Date Posted: 20 Jun 2025 at 2:35pm

Scenario: I first encountered this on a VFR flight where the destination airport was unexpectedly IMC. So with no flight plan, I simply entered the approach and went direct the IAF (with clearance, of course!). Did not get the "suspended" message that time, but the autopilot didn't capture the glideslope, and I flew it manually.

Then went out to reenact the scenario at my home airport (KAVL), to try to figure out what happened. No flight plan in the 540, just a radar vectors to the RNAV 35, and on three tries, got the "suspended" message three times.

I don't understand! It's worked fine in the past...

Posted By: dmtidler
Date Posted: 20 Jun 2025 at 4:48pm

Using the GFC500 autopilot, there should be an FMA on the upper part of the flight display used in conjunction with the GFC500. I'm curious what displayed flight modes were active/armed shown on the flight displays as well as the IFD indicated Nav Source on the upper right corner of the IFD both before and after the "VNAV Suspended" advisory?

I think it is possible to not get a VNAV termination advisory if a VNAV Enabled IFD never gets to an enroute TOD point (i.e. the aircraft is operated below the IFD descent path for the entirety of an enroute descent).