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DFC90 with 430W and LPV Approaches

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stlsmiths View Drop Down
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    Posted: 17 Oct 2011 at 2:18pm
Hello All,

I'm a newly registered member on this forum.  I own an SR-22 G2 and am upgrading my dual 430 with STec55X to a WAAS dual 430W and DFC90 system.  The upgrade will include the Release 8 upgrade to the PFD.  My bird will be going into the avionics shop in the next couple of weeks.

I was reviewing the DFC90 POH and noticed a statement regarding WAAS approaches (Pgs 4-2 to 4).  It says that any WAAS approach is intended to be flown with the primary CDI set to GPS1 or 2 but using the NAV APPR modes and not GPSS mode.  The description continues by saying the the 430W issues roll commands instead of the DFC90.  "Glide slope will not arm if the autopilot mode is GPSS".  Then in a later paragraph it states that if the a/p is left in GPSS mode when a valid glideslope signal is received it will automatically switch back over to NAV APPR mode.

Can somebody please clarify using the DFC90 for coupled-WAAS for me a little bit?   Specifically, what actions does the pilot take on the DFC90 when flying an LPV (or any WAAS vertical guidance mode) approach after loading the approach in the 430W (for either a IAF or VTF approach) through capturing the HDI and GS signals?

I'm sure it will be clearer once my install is complete and I begin flight-testing, but figured I would throw it out there to the experts!

Thanks for your responses,

Todd

P.S. - And just for completeness, if I were so lucky to have Rel 9 with DFC100 would the LPV be flown using GPSS APPR ??


Edited by stlsmiths - 17 Oct 2011 at 2:25pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 17 Oct 2011 at 3:09pm
Hi Todd,

Thanks for the question and welcome to the AvidyneLive forum.

As you may have picked up from the text, GPSS mode from the Garmin 430W does not guarantee proper vertical guidance, including during WAAS approaches.  Because of this, we don't allow a pilot to fly a glide slope of any kind (ILS or WAAS) with the autopilot in GPSS mode.

I tried to write the DFC90 Pilot Guide to describe the button pressing operation on both the PFD and DFC.    The objective is to ensure the PFD has the Primary Nav button set to GPS1 or GPS2 and to ensure the DFC90 is in NAV APPR mode (both NAV and APPR buttons lit in green).  

The text in the Pilot Guide recommends the pilot to use the mode switching automation in the PFD and the DFC90 and was mostly written with that automation in mind.  To directly answer your question, assuming the desired approach has been properly loaded in your Garmin(s):

1.  Make sure the 430Ws are set such that the "ILS CDI Selection" setup option is set to Auto.
2.  Do not manually select VLOC1 or VLOC2 on the PFD Primary Nav LSK.  Said differently, ensure the PFD Primary Nav LSK is set to GPS1 or GPS2 and don't press that button again yourself during the approach - be sure to pick the GPS in which you loaded the WAAS approach.

Note:  It is likely you were in GPSS mode on the DFC90 if you were flying enroute and ending the flight with this WAAS approach.  And, because you've set up the 430W to auto slew  per step 1 above and you've loaded and activated the approach in the 430W, then you shouldn't have to press any more buttons.

3.  Near the Final Approach Fix, the autopilot will automatically switch from GPSS (if it was in that mode) to NAV APPR and you will also see the GS button on the autopilot arm (cyan blue color). 
4.  As glideslope is intercepted, GS will transition from armed (blue color) to captured (green color) in addition to NAV APPR.

And in R9, the operation is much slicker.  There is no GPSS mode.   You just use Nav mode and there is much more automation in the auto switching.  If you're interested, you can view the R9 and DFC100 user manuals from this forum or the main Avidyne website.  Need a link?

Does that clear it up for you or should we keep trying?

Steve


Steve Jacobson
sjacobson@avidyne.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stlsmiths Quote  Post ReplyReply Direct Link To This Post Posted: 17 Oct 2011 at 4:19pm
Hi Steve,

Yes I think you cleared up what I was asking for.  I have been accustomed in the 430/STec world to using the GPSS mode for the enroute mode and even for DME arcs and course reversals, then while inbound on an approach flying via NAV APPR (assuming auto switch mode is on).  Sounds like the same technique applies for the DFC90. 

So I will remain hands-off and not switch the nav source while flying the approaches, and let the avionics system do the work.

From what I read in your POH, if the GS is not captured from below (on an ILS - as it seems I often get "dropped in" from above by ATC!) and if I am below the obvious false glideslopes but prior to FAF I can still use the GS button on the DFC90 to attempt to capture the glideslope, correct?  (a little off LPV topic, as I don't think LPV's show "false glideslopes"...)

For curiosity sake I will review the R9 / DFC100 docs, but will probably have to replenish my funds (and or win a lotto) before I can do that upgrade.

Thanks again,

Todd


Edited by stlsmiths - 17 Oct 2011 at 4:22pm
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