DFC90/DFC100 Digital Autopilot - DFC90: Activating the APPR button on the ILS

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DFC90: Activating the APPR button on the ILS

Printed From: Avidyne
Category: Avidyne General
Forum Name: DFC90/DFC100 Digital Autopilot
Forum Description: Topics on the Avidyne DFC Digital Autopilots
URL: https://avidynelive.com/forum_posts.asp?TID=231
Printed Date: 26 Mar 2026 at 4:31pm
Software Version: Web Wiz Forums 12.07 - https://www.webwizforums.com

Topic: DFC90: Activating the APPR button on the ILS

Posted By: RogerHarr
Subject: DFC90: Activating the APPR button on the ILS
Date Posted: 19 Sep 2012 at 10:48pm

http://www.cirruspilots.org/forums/ReportAbuse.aspx?ForumID=1&ReportPostID=674054 - - Reply | http://www.cirruspilots.org/forums/p/131521/674490.aspx# - Roger Harr Posted: 18/9/2012 20:40

I have my DFC90 now 18 months and it worked without any problem.

During several - not all - of my last ILS approaches I had a problem with the DFC90. It was not possible to activate the APPR function after intercepting the localizer while flying a vectors-to-final approach with the heading bug. Perfectly aligned on the localizer with PFD in the VLOC mode nothing happened while pushing the APPR button. The button stayed dark. The only solution was to press the AP Disconnect switch on the control yoke and to activate the DFC90 again.

Doing the pre-flight test of the DFC90 there is no sign of an abnormality.

- Is there a problem with the autopilot or did I omit something?

- Or other question: What do I have to do wrong, that it is not possible to activate the APPR mode?

Replies:

Posted By: AviJake
Date Posted: 20 Sep 2012 at 3:36am

HI Roger,

I think I may need some more info. You can elect to either answer here so that others may see the interaction or send me a direct email at sjacobson@avidyne.com.

As for the extra information (I apologize for any sophomoric sounding questions):

1. I see you have the PFD in VLOC mode. Can you confirm that Primary Nav was indeed tuned to the proper localizer frequency?
2. Can you confirm you had the proper inbound course set in the Primary Nav datablock?
3. What is your typical technique on Vectors-To-Final approaches? My normal technique is to be in HDG mode and then when either cleared for the approach by ATC or when established on final, I arm NAV APPR by pressing the HDG & NAV (or APPR) buttons on the autopilot at the same time. Pressing either HDG-NAV or HDG-APPR will work and the other one (APPR or NAV) "comes along for the ride" but my habit is to press HDG NAV. At that point, I should see HDG in green and NAV and APPR lit up in blue. It is possible that the capture criteria are immediately satisfied so it might be a near immediate transition to no HDG and just solid green NAV and APPR.
4. Do you ever have NAV lit up in green on the DFC control panel and in the PFD annunciator strip?

To answer your last question about conditions that may prevent activation of APPR, there are a few. In general terms, you need to have the proper freq and selected course dialed in, the radio needs to see the VHF signal, and you've got to be pretty closely aligned with the final approach course and inside 18nm.

-------------
Steve Jacobson
sjacobson@avidyne.com

Posted By: RogerHarr
Date Posted: 20 Sep 2012 at 6:32am

To answer your questions:

Tuesday I did two approaches at my homebase LSZB in VFR conditions to test the system. I already took off with the correct localizer frequency on NAV1. I can also confirm that I had the correct distance indication on my DME.
I had the proper inbound course of 139 for the localizer.
My standard procedure is: Using the HDG bug to intercept the localizer. When intercepting the localizer I switch from the GPSS to the APPR mode with pressing the APPR button (and that is where sometimes nothing happens).
Yes

Doing the first approach I had to switch off the autopilot around 9 miles out. After switching it on again, it was possible to activate the APPR mode. Doing the second approach it worked normal.

What if I try to make some pictures of my avionic settings during an approach in VMC conditions tomorrow?