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Old 08-18-2015, 08:06 PM
RV9Otter RV9Otter is offline
Join Date: Mar 2015
Location: Dadeville, Alabama
Posts: 69
Default No Vertical Guidance On GNS 430W

I have a GNS 430W feeding a pair of GRT Horizon EFIS's with a Digiflight IIVS auto pilot. I've been doing practice GPS approaches to my home airport of KALX for weeks and all systems have been working as expected. Today, however, I could not get a vertical guidance to work no matter what I tried. I was also getting the "FLG" which I think means "flagged" on the auto pilot vertical guidance. The "localizer" vertical line was showing up on the EFIS and working correctly throughout the approaches, but, I could not get any vertical guidance to work (the vertical guidance bar never showed up on the EFIS).

In summary, I could get the "localizer" bar to work and the autopilot to track the localizer, but, could not get the vertical guidance bar nor would the autopilot track the vertical guidance as it usually does.

I can't find any clues in the manuals.

KALX has an LP approach.

I'm 99% certain that all systems are working correctly...and that I'm not operating something correctly in the GARMIN 430 or the GRT EFIS.


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Old 08-18-2015, 08:19 PM
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Radomir Radomir is offline
Join Date: Jan 2005
Location: Charlotte, NC
Posts: 1,524

Which runway? there won't be any vertical guidance on RNAV 18, since that has LP minimums. If you update your 430W's software to the very latest (5.2), you will get advisory guidance (aka LP+V).. Though RNAV 36 should have worked since it has LPV minimums.

Furthermore RNAV 18 has Descent Angle N/A annotated, and with older software versions that one won't even show up in the database (you can't even select that one), unless you update the 430..
RV-7A sold
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Old 08-18-2015, 09:47 PM
RV9Otter RV9Otter is offline
Join Date: Mar 2015
Location: Dadeville, Alabama
Posts: 69
Default Thanks for the are right.

Actually, I obviously have some learning to do regarding GPS approaches. It was on 36 that I received vertical guidance and not on 18. 36 is LPV and 18 is simply LP. Equipment is fine...pilot still learning. Thanks. Curt
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Old 08-18-2015, 11:34 PM
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MCA MCA is offline
Join Date: Jun 2005
Posts: 705

The lateral and vertical deviation data come into the GRT from the G430W over the same data line. Therefore if the lateral is coming in then the vertical must be coming in as well. Sounds like a setting in the GRT or 430 might have been changed inadvertently.

My 2 cents...
Marc Ausman
RV-7 980 hours, IO-390, VP-X (sold)
RV-8 (flying a friend's)
Thinking about low and slow backcountry build.
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Old 08-19-2015, 08:48 AM
Dan B Dan B is offline
Join Date: Mar 2006
Location: Edmond, OK
Posts: 199

The KALX RNAV (GPS) RWY 18, Amdt 1 approach has LP and LNAV minima. The vertical guidance is not included in the navigation database because a 3.00 degree glide path would fly you into, or too close to obstructions once you descend below MDA inbound to the runway. Therefore, the database glide path is not coded. That is why you get a glide path flag. For this approach, your system is working properly if it is flagging the glide path. The FAA design criteria is to not provide a navigation database glide path that does not provide adequate obstruction clearance to the threshold.
Dan Burdette
Skyview, Garmin GTN750xi, TT Gemini AP
RV-9A, IO-320
Guthrie-Edmond Rgnl, OK (KGOK)
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Old 08-19-2015, 02:24 PM
RV9Otter RV9Otter is offline
Join Date: Mar 2015
Location: Dadeville, Alabama
Posts: 69
Default Thank You

Thanks for the replies...all were helpful. The GPS 18 approach at KALX does not provide vertical guidance...which is why I was not getting any. My prior practice approaches were done on GPS 36, which does provide vertical guidance. I'm not new to IFR but am new to GPS approaches and the equipment in my RV9A. As I said, the "problem" was me...not the equipment. Thanks. Curt
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