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DFC90 - GPSS vs. NAV Mode

Printed From: Avidyne
Category: Avidyne General
Forum Name: DFC90/DFC100 Digital Autopilot
Forum Description: Topics on the Avidyne DFC Digital Autopilots
Printed Date: 25 Jun 2022 at 4:12am
Software Version: Web Wiz Forums 12.01 -

Topic: DFC90 - GPSS vs. NAV Mode
Posted By: GYORC
Subject: DFC90 - GPSS vs. NAV Mode
Date Posted: 04 Aug 2013 at 10:14am
Hello Avidyne,

beiing a proud owner of a DFC90 in my SR22 for 4 weeks now, I still sometimes feel like a passenger when the A/P does not do what I expect it to do. I must admit I find it hard to learn how the different modes are used – and the DFC90 manual is really not a big help. (Most of the what I learned about how to use the A/P I found in the S-TEC55X manual.

Don't get me wrong here: I think you have a wonderful product (and actually I was responsible for 3 of your DFC90 sales lately and one more of my friends is installing it - now that i told him it's a good investment for his SR22. So, i guess I am not really your enemy :-)

But I think Avidyne should make an investment into a good manual that covers ALL the aspects of the A/P. The baseline: I think the A/P is a very good product - but why is there no good training material ? A simulator would actually be the best thing to have. Too expensive to make? After all I plan to (one day!) fly my SR22 in IMC with your autopilot and my kids in the backseat. To me that is reason enough to get all the details from you.

My main problems circle around the use of the A/P on a typical ILS approach. My airplane is a 2006 Avidyne equipped SR22, with two non-WAAS GNS430s.

The scenario: I fly a typical Standard ILS Approach in Germany, EDMA airport in Bavaria, ILS 25. IAF is WLD VOR. Hold over the VOR. Approach is out of WLD on r-132 to DME 4, right turn to intercept FC 250....

What I have found out is that the A/P will fly directly into the Intermediate Approach in GPSS mode, without crossing the IAF first. But actually i wanted to fly into the hold for practice .... So, to CROSS the VOR into the hold I switched off GPSS and crossed the VOR in HDG mode and made the turn back to the VOR (inbound leg of hold) with HDG too. In the middle of the inbound leg i switched to GPSS and the A/P would nicely fly me out of the hold and into the intermediate approach on r-132.

This is where the "problems" start. Or at least it is not completely clear to me. I have GPSS ON and the A/P will even turn twds the Final. I have the ILS frequency tuned in on Nav 1 and the LSK 1 on the PFD says GPS 1. CDI Mode (430): GPS. The A/P will intercept the localizer but never arm the APP mode or the GS. The GPS (yes, "Auto CDI ON") did not even switch from GPS to VLOC, the Final course was not set.

Is my mistake that I mix up "GPS" (CDI key on navigator) and "GPSS (GPSS key on A/P)?

The A/P will ONLY  switch from GPS to VLOC if I press NAV at the right moment of the intercept (it seems). Only then it will also arm the GS and fly the approach. Why? There is no transition from GPSS to APP automatically? There are some hints in the manual but i dont think it's really clear - at least not to the newcomer.

Now I asked some very experienced COPA members and what they said, in general, was: "FORGET THE GPSS MODE, FLY IN NAV MODE ONLY AND EVERYTHING WILL BE SIMPLE". Beeing a journalist I tried to find out more. The pros keep telling me that i do not need GPSS at all, and that the A/P will fly "just as precisely" with NAV only, and that "GPSS is a thing of the past" which the DFC90 does not need.

Isn't the idea that GPSS will use direct input fro the navigator while NAV will fly the information the HSI displays on the screen. I understand (now) that NAV uses GPS as well when the CDI Key is in "GPS" mode and not VLOC.

All that is very new to me (because I thought the A/P would only fly a GPS flight plan precisely and with nice turns) on GPSS. Now I am beeing told that with the DFC90 the GPSS mode is un-necessary and that I should only fly using NAV - and that it will work better then. But ... why does the A/P HAVE a GPSS mode then? 

It would be great if someone from Avidyne could give me some background information and ESPECIALLY tell me what the best way is to fly a STANDARD ILS PROCEDURE with my setup. WHICH MODE DO I USE AT WHAT POINT IN THE APPROACH? Should I forget about GPSS once I get close to the airport? Should I try HDG+NAV? 

Kind regards,

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: AviJake
Date Posted: 07 Aug 2013 at 6:53pm
Hi Alexis,

There are a lot of nuanced details/questions in there that I'll plan to respond in greater depth in a follow-up post.  Before I do, some questions for you:

1. Are you observing some behavioral differences with the autopilot in NAV vs GPSS?   (You shouldn't see any difference).  GPSS is a legacy holdover for all those pilots who were used to that mode prior to the DFC90.   There is no algorithmic difference between the two in the DFC90.

2. By "Standard ILS Procedure", do you mean the full published approach or a Vectors-To-Final scenario?

Steve Jacobson

Posted By: GYORC
Date Posted: 08 Aug 2013 at 3:16am
Hello, thanks for answering!

1. I never really compared NAV and GPSS enroute, because for me that is really two different things. As your manual states the nav comes directly from the navigator in GPSS mode, while it should come frome the PFD or the PFD's HSI in NAV mode.... I have not tried if the A/P will ANTICIPATE a turn in NAV mode. (Will it?) I HAVE used GPSS or NAV while intercepting an ILS. Result: In GPSS the A/P would intercept the Final course but never switch to VLOC and never arm or intercept the GS. In NAV mode both worked.
If GPSS and NAV are exactly the same - why this difference?

2. Standard ILS procedure means the FULL APRROACH. To the IAF (into the hold), outbound the IAF towards the final, intercepting final

Are you saying that the Autopilot has a NAV and a GPSS key and they do exactly the same???? I could hardly believe that ... Why would somebody build a unit that has two keys that do exactly the same?

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: achimha
Date Posted: 08 Aug 2013 at 5:54am

I think you are talking about the autopilot when in reality you should be talking about the GNS430. The autopilot does not control the GNS430, it is the other way around.

Remember what AkiJake said: NAV and GPSS are the same thing. Historically, GPSS was an add on and implemented by putting the AP in HDG mode and having an external unit calculate headings and feed them to the AP. In the DFC90, it's all done by the AP itself. It's great that the DFC90 takes roll steering information (i.e. GPSS) in NAV mode and the additional GPSS button is just a convenience for pilots that expect it.

Your GNS430 needs to be in VLOC mode to fly an ILS. It is either you as the user or the GNS430 itself (auto mode) that switches from GPS to VLOC. Don't blame the DFC90 for that.

Same thing about your holding, you are blaming the DFC90 while you are talking about something that only concerns the GNS430. The GNS430 does not help you in flying holdings unless they are part of the procedure (which is not true for the Walda holding). What you do is press OBS before you arrive at WLD (suspend sequencing) and then use the heading bug to fly the holding. You can get some assistance by setting up an OBS with the holding inbound radial. This allows you to better aim at the inbound course and you could even use NAV mode to let the AP intercept the holding inbound course. However, I find that to be of limited use because you end up turning a lot of knobs for little benefit (you have to basically leave the approach flight plan and do a direct on the fix with an OBS set). I do setup the OBS to show the inbound course but usually on my Garmin 695 to not have to reconfigure the 430 and I use the heading bug and the AP in HDG mode to fly the holding. Once I am cleared for the approach and on the inbound radial to the holding fix, I make sure the right leg is active in my approach and then switch the DFC90 from HDG to NAV. It will then fly to the holding and perform the full procedure, including turning to final and -- once the GNS430 switches from GPS to VLOC -- fly the ILS.

I too had a DFC90 installed a few weeks ago and I found the user manual to be very good. What it was lacking is a detailed description of how the autopilot works internally. The fact that it is constantly driving the pitch trim (in a Cessna) was driving me crazy because this is fundamentally different from all the others. Talking about user manuals, the GNS430 manual is a great example of a rather poor manual that raises more questions than it answers.

Posted By: GYORC
Date Posted: 08 Aug 2013 at 1:06pm
Hi Achima, not all of what you write convinces, some does!
I cannot believe that an Avionics Company makes an Autopilot with TWO SWITCHES that do exactly the same. None of this described in the manual, and not even a STANDARD ILS is described, only one with Vectors. Believe me, beeing a former technical (for computer comapnies like Microsoft) and a longtime aviation journalist i can recognize a good manual when i see it.

A GOOD indication for how lousy the manual is is that I talked to (a couple of) Cirrus "standardized" Instructors (and I mean the well known ones) and other "experts" and each of them said something different. Nobody could explain the whole procedure to me or the function of the  keys.

Also: a good manual is one that i UNDERSTAND and that answers my questions. It's really that simple.

YOUR explanation about how to fly the approach is the best so far, I will try that. Although I see other possibilites too, like flying to the IAF with GPSS, switching over to HDG to fly the holding entry, then GPSS to again to fly out the hold into the intermediate approach ...the NAV for the intercept.

Of course your method is much better. You are in Bavaria, right? Is your Cessna green? ;-)

I want to know from Avidyne: What is the difference between using the GPSS key and the NAV key. OF COURSE one difference is that the A/P will NOT activate the approach and GS - while NAV does! YOu have to fly in NAV to have the automatic switchover from GPS to VLOC in the GNS430.

My personal opinion: In a completely over regulated flying world in which I need an engineer, a witness and probably a notary if i want to change the landing light bulb - the manual for an IFR (!) autopilot should cover each and every aspect of it, have illustrations, tables, graphics and explaining ALL TECHNICAL BACKGROUND. We are not talking about a coffee maker - the target group of this product is one that is interested in technology. And it's a product that can save your life - or kill you. And the people who don't want to read it, will not anyway.

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: GYORC
Date Posted: 08 Aug 2013 at 1:07pm
(I did never say that I expect the DFC90 to automatically fly the holding. And I know the GNS430 well, i had one in my Piper for 13 years before I bough the Cirrus.

It is also interesting what you say about the GNS430 manual ;-) While it also lacks some details - in comparison to the DFC90 there's much more information it. And a downloadable sim.

The SR22 has a pitch SERVO so it does not use the trim for the A/P. But in the SR20 you'd have the same configuration like in the Cessna, unless you install a pitch servo, which is RECOMMENDED, but vcery expensive ...

FROM  the Avidyne Website:

"There are many other improvements, such as a dedicated Vertical Speed knob, pitch hold mode, wide autopilot engagement, additional annunciations in PFD 8.0, a dedicated GPSS button, automatic Back Course Approach selection, multiple color annunciations to indicate armed and active states, intercept mode annunciations, and Avidyne’s hallmark ease of use."

Now, if NAV and GPSS does exactly the same - why is "a dedicated GPSS button" an improvement? Is it maybe if the DFC90 is installed in other aircraft?

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: wsh
Date Posted: 08 Aug 2013 at 8:32pm

I am following this link with some surprise.

My ac is equipped with 530/430 non waas, a kfc200 and an Aspen which will allow for gpss steering. Since the Aspen I no longer fly in Nav mode but allways in heading mode with gpss.

The main difference is that it will automatically change course whenyou arrive at a waypoint. In nav mode it does not do this. Having said that i wunder why it would not do that with the Aspen...

Now when arriving at an ILS I will be in hdg/gpss and the garmins in gps.. It will go to the iaf and intercept .. At that point .. The garmins will automatically change to vloc. This is the part Were I loose you. I believe the Garmin itaelf makes the switch and not that it does this by a signal from the ap?

All I need to do is monitor wether the switch was made and check or switch the ap to approach mode.

Posted By: achimha
Date Posted: 09 Aug 2013 at 3:25am
And I know the GNS430 well, i had one in my Piper for 13 years before I bough the Cirrus.

Then you will know by heart how important it is to make sure the VLOC/GPS toggle is correct and that it is either the user or the GNS430 that switches between the modes and never the autopilot. GNS controls the AP, not the other way around.

The SR22 has a pitch SERVO so it does not use the trim for the A/P. But in the SR20 you'd have the same configuration like in the Cessna

The C182 has a pitch and pitch trim servo (both required by the DFC90 STC). All other autopilots would use the pitch servo to control pitch and in case of excessive forces (OOT - out of trim) run the pitch trim to remove those. The DFC90 is radically different in that regard, it constantly drives the pitch trim servo and very rarely the pitch servo. In the C182 you can observe this very well but in the Cirrus you don't see that due to no manual trim. This unique behavior caused a lot of confusion for me and my shop because it is so different from everything else. But hey, it works great.

Back to the GPSS/NAV issue. When the GNS430 is in VLOC mode (required for ILS), traditional APs would not provide GPSS at all (e.g. my previous S-TEC 60-2 with Aspen's GPSS). The DFC90 can do GPSS even when the 430 is in VLOC mode by pressing the GPSS button. My previous AP would do funny things if it was in GPSS and the 430 in VLOC mode. A major source of errors. No more.

When flying an ILS, you could use GPSS or NAV to fly the procedure from the IAF to the FAF and once you are supposed to capture the ILS, you or the GNS430 would switch to VLOC. The DFC90 will then switch to NAV. If your GNS430 is set to GPS (i.e. not VLOC), then NAV and GPSS would do the same thing on the DFC90 because even in NAV mode it uses the roll steering data and not the CDI data. However, if the 430 is in VLOC mode, then NAV obviously is CDI based.

Another thing that is different with the DFC90 is that it does not care whether you intercept an ILS from below or above. The S-TECs would not do intercepts from above unless you force them. With the DFC90's color codes it is very easy to spot what mode you're in (green) and what it plans to achieve (armed - light blue) and when it's is getting there (capture - blinking green). I find the user interface of the DFC90 to be exceptionally good. If I had one wish, I would ask for a third knob to select altitude.

You are in Bavaria, right? Is your Cessna green?

I take that as an insult :-) Answer is 2x a big NOOO. I am in Stuttgart.

Posted By: GYORC
Date Posted: 09 Aug 2013 at 3:46am
I will have to read that a couple of times, before i will (maybe) understand it. Now there SEEMS to be a difference between GPSS and NAV again while I was just trying to accept that there should be "no difference in behaviour" between GPSS and NAV, see first reply.

And you think the manual makes all this clear?

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: achimha
Date Posted: 09 Aug 2013 at 4:12am
GPSS/NAV are the same when the 430 is in GPS mode.

Having taken another look at the user manual, I have to agree. It could be clearer on this and have more examples. I somehow had the impression that chapter was clear, I mixed it up with the Aspen manual which is the best user manual I've come across so far.

PS: Let me describe how I flew an LPV approach into EDTY (Schwäbisch Hall) the other day. The approach starts the DKB VOR, I was on a flight plan to EDTY and I chose PROC on the 430, selected RNAV 28 with IAF DKB and activated the approach. The DFC90 was on GPSS.

This was everything I had to do, the 430/DFC90 flew me to the IAP, made the described turn to the IF, turned to the final course, intercepted the "glideslope" and started descending. I did not touch the DFC90 or the 430, I only operated the throttle (yeah, I need autothrottle), gear and flaps. The autopilot did everything by itself and both the annunciator in the Aspen and the lights on the DFC90 showed me exactly what state it was in and what it was trying to achieve.

I then did the very same thing with the ILS 28 in EDTY and the 430 automatically switched from GPS to VLOC and the DFC90 from GPSS to NAV. Same experience as with the LPV.

The other day I had my yearly IR checkride (a European thing) and the examiner wanted me to fly a non precision approach so I can show him how well I manage a continuous descent. What he didn't know was that there is an LPV now (a very recent thing in Europe) and that the 430 would automatically go for LPV when loading the RNAV approach. I pretended to control the sink rate with the trim switch and kept reading check altitudes. In reality, the DFC90 was flying the LPV approach all the time. The instructor was impressed by my manual flying skills :)

Posted By: GYORC
Date Posted: 09 Aug 2013 at 5:20am
Haha... I could have done that ;-) Very cool. 12 years ago, on my IFR checkride, the examiner did not realize that I had a DIRECT to the airport in the GPS which showed me the bearing on the NDB approach. Or maybe he saw it and didn't care ...

I have to further test all this (probably spend € 1000 on fuel before I fully understand it)
My SR22 doesn't have the WAAS 430s, and all I am really interested in is flying ILS and GPS approach procedures safely.

But, again, when I intercepted the LOC with GPSS the system did NOT switch from GPSS to AV automatically, nor did it set the Final Course as it should. It only did all this in "NAV".

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: achimha
Date Posted: 09 Aug 2013 at 6:19am
But, again, when I intercepted the LOC with GPSS the system did NOT switch from GPSS to AV automatically, nor did it set the Final Course as it should. It only did all this in "NAV".

The AP does not set the course pointer, that the job of the 430. The switch from GPS to VLOC is also the job of the 430. It has nothing to do with the DFC90 being installed or not. Did you load the ILS approach and activate it? I made the mistake of not activating the approach many times. I very much remember when that happened in Dubrovnik LDDU and instead of intercepting the glideslope, it flew directly towards the mountain. I was focused on ATC and charts when I should have focused on flying and the mountains came close. All because of the stupid Load vs Activate thing in the 430.

Posted By: GYORC
Date Posted: 09 Aug 2013 at 6:53am
I really don't care which unit is "responsible" (i do not intend to sue my autpilot ;-)) ... I just said it DOESN'T WORK.

Before I make anymore big mouthed statements I'll check if the Approach was really activated. BUT: If I activate the approach then it will always start at the IAF, right (or fly to the IAF first, correct?) So I would have to use the "SUSP/OBS" method to fly through the holding, correct?.., Then GPSS to the Final and then everything should work automatically, yes?

GNS is set to CDI Auto, by the way ...

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: achimha
Date Posted: 09 Aug 2013 at 7:09am
If I activate the approach then it will always start at the IAF, right (or fly to the IAF first, correct?) So I would have to use the "SUSP/OBS" method to fly through the holding, correct?.., Then GPSS to the Final and then everything should work automatically, yes?

You can choose IA or Vectors to Final when activating the approach but in your case IA would be correct and yes, if you actually want to fly the hold, you press SUSP/OBS so it stops sequencing and keeps the holding fix as the current next waypoint, then switch the DFC90 from GPSS to HDG and use the knob to fly the holding and once you are on the last inbound leg to the holding fix/IAF, you switch the autopilot to NAV. It will resume navigation, fly to the IAF and continue sequencing. Provided that your GNS actually switches from GPS to VLOC at the right time and also slews the course pointer to the ILS course (again, that has nothing to do with the DFC90), the autopilot will fly the ILS.

I really don't care which unit is "responsible"

Sure but one has to carefully understand which unit does what and how they interact. Avidyne didn't design the 430. It's all nontrivial and I hope I got the above procedure right from memory.

BTW: A DFC90 simulator doesn't make much sense. It would have to be a GNS430 + DFC90 + Avidyne/Aspen simulator and that is a bit of a far stretch for Avidyne. The best hope would be one of the flight simulators if somebody implements the DFC90 as an add on module. I've learned a lot about the 430 by using X-Plane.

Posted By: GYORC
Date Posted: 09 Aug 2013 at 7:17am
Thanks for the tipps.. I will try all that next time!

Of course I know that Avidyne did not design the 430. But somebody should tell you how that whole system REALLY works, and since the GNS430 manual existed years before the DFC90 in this case Avidyne should tell people how it really works, with every detail and every possible scenario too. O mean it is a RETROFIT for an avidyne equipped Cirrus with GNS430!

A DFC90 module for FSX or Xplane would be easy to do. Avidyne equipped aircraft for FSX already exist.You can have the Space Shuttle's Avionics on the net ...

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: MysticCobra
Date Posted: 09 Aug 2013 at 11:52am
No company likes to include instructions on how another company's device works, especially something as sophisticated as a GNS-430.

Garmin has updated the software in the GNS units over the years, introducing some subtle and some not-so-subtle differences in behavior.

Who would you blame if you got an Avidyne manual that included instructions on how to operate the GNS-430, and those instructions were wrong because Garmin updated the software since the manual was published?

My aircraft came with a 12-page booklet of "instructions" for how to fly it.  Sometimes, the things you would like to know just aren't in the manual.

Posted By: GYORC
Date Posted: 09 Aug 2013 at 11:55am
My opinion is different: The DFC90 is a RETROFIT for exactly this avionics suite in the Cirrus, and therefore it has to be explained how it will work/react in this environment. If I don't understand how it works, then the manual is bad.

It might be that aircraft come with 12 page manuals. But I do not have to like that. And I don't. In 1940 Chuck Yeager was introduced to a fighter aircraft by an instructor: "You close the canopy. At 70 mph you take-off and raise the flaps at 100. Landing works the other way round". We could have left it at that level, right?

I don't even say that everything has to be in the manual. But maybe it would be appropriate to give the pilot access to the necessary information?

If you don't want it - don't read it! :-) I do want it, and I know why.

Ahh... and about the possible update of Garmin's software: Thats what they invented updates for manuals for. Is done all the time. 

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: achimha
Date Posted: 12 Aug 2013 at 1:23am
I disagree with what you say, Avidyne does not produce the GNS430 and it's not even required in a DFC90 install but anyway, here's how I flew an ILS into EDAH Heringsdorf on Saturday.

I was coming from the south and was cleared for a standard ILS 28 (about the only German airport without radar vectored ILS because the approach is over Polish territory and Poland does not publish MRVAs which prohibits radar vectoring under German regulation). So I loaded the approach on the GNS with the HC beacon as the IA. The GNS was configured for GPS and the DFC90 was in NAV mode. It correctly flew to HC, turned right on track 113 for the outbound procedure turn, then turned onto final 277. I then activated the backup ILS frequency which the GNS put there (it does not activate it itself) and was watching. Once I was on the final leg of the approach, the GNS automatically switched from GPS to VLOC, the course pointer was auto-slewed to 277 and the DFC lighted the APPR light and armed the GS. A bit later it was established and started the descent. This time I didn't do anything at all, no gear, flaps or throttle because there was an airline behind my back and ATC asked for 140 IAS until 4NM :-)

I find this setup to so much better than my previous S-TEC install. The DFC knows what to do and has a great visual representation of its current and future state.

Had I stayed in GPSS mode, the DFC would not have armed the approach. Therefore, put the GNS in GPS mode and the DFC in NAV mode when loading an approach.

Posted By: GYORC
Date Posted: 12 Aug 2013 at 3:24am
Of course you don't have to agree. But as i said before: Avidyne advertises this system as a retrofit for Avidyne + Garmin GNS430 equipped SR22s. They even write "takes full advantage of the 430's automatic switching ...." and so on (wording from memory).

So you think it is asking too much if i want a manual (website, call, smoke signals) that explains in detail how the A/P will work?

I like the autopilot as much as you do. I even helped Avidyne sell three of them to friends (actively!). But a good technical description is the minimum i could ask for.

Yes, I will only use NAV for ILS, just as you described. I was in Heringsdorf a week ago!

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: AviJake
Date Posted: 20 Aug 2013 at 1:45pm

For better (or I guess worse), I am the sole author of the DFC90 Pilot Guide.   Although I do like the Chuck Yeager school of instruction and naturally tend more toward that school of thought, I'm sure it's always possible to improve a manual.  

Do you still have specific questions or have they been resolved by now?
Do you have specific recommended changes to the manual or just a general wish for more detail?

One side note, the book is very expensive to print and distribute and we haven't found a loop hole that allows for one version in electronic form and one version in print form.   Additionally, we try to keep ourselves out of the training environment and leave that to the training professionals.

Not trying to whine or deflect/dodge the issue - just want to lay it all out there.

How do you recommend we proceed?

BTW, if you or anyone want to provide or suggest actual wording/content, I'm in complete support of that possibility.

Steve Jacobson

Posted By: GYORC
Date Posted: 21 Aug 2013 at 7:02am
Dear Jake

at the moment i am on vacation in Greece, 1800 km away from my plane :-(

I thank you very much for your kind reply and if you want i am more than willing to help you improve the manual a bit.

Believe me, it's hard for me to critisize other writer's work, especially since I'm an aviation journalist, book author and former magazine editor.

If i can help, i will and for free. Just give me a little time to think about my specific questions and about how the manual could maybe be improved a bit!

you'll hear from me soon!
Alexis von Croy

sent from iphone

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: GYORC
Date Posted: 03 Oct 2013 at 9:40am
Hi AviJake,
as you can see in my other/new thread at the moment I am havig other problems with my DFC90, it simply disconnecst itself in cruise and I have not found the reason yet.

About the Manual: I understad that it is (legally?) a problem to have a new electronic manual and that you would have to print a new paper version aswell. On the other hand it should be no problem to put the necessary information on your website.

You say you want to "keep yourself out of the training environment and leave that to the professionals"
Well, I have tried for THREE MONTHS now to find such a professional here in Germany and (no names) even the ones who really should know how it works all tell me different things. One of them even flew with me ("I'll show you") even flew with me and when he pressed some buttons for the ILS approach and the a/c turned the wrong way he went "well, it shouldn't do that"...A bit later he admitted that he knows the new Perspective planes better ....

So, maybe you can give me a name of a Flight Instructor in Germany who REALLY knwos the GNS430/DFC90 combination and could teach me how it is flown.

It is not helpful to leave all this to the "pro's" when you can't find one who really knwos what he's talking about.

About the manual: It would be VERY helpful if the manual contained graphics of different approaches and scenarios that showned precisley WHERE to push which button. The problem I have is that when you are a beginner with a new technology you cannot NAME the parts that were bad in the manual. I only know that I don't understand it and that there seems to be a lot missing (Standard ILS Approach via IAF...)

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

Posted By: AviJake
Date Posted: 04 Oct 2013 at 9:13am
Looking.  Hopefully answer is delivered to you on the same call that should resolve your roll servo question from a different thread.

Steve Jacobson

Posted By: Melohn
Date Posted: 12 Dec 2013 at 4:02pm

I'm a new and generally happy owner of an SR-20 with a DFC90. I have a specific recommendation for you to consider in any revision of the manual, or perhaps for a less formal FOM that could accompany the current guide:

Page 3-4: There is a note that says the following:

Approaches with Curved Paths Must Use GPSS                          
Certain GPS procedures involving curved paths can
not be flown in NAV mode (e.g. holds, DME arcs,
etc). GPSS mode must be used for those

This appears not only to be incorrect, but also incomplete in an important way; if you fly an ILS with a DME arc with the DFC90 in GPSS mode, the ILS portion of the approach will NOT arm. You MUST be in NAV (or perhaps APPR) mode for this to sequence properly. From what I've read, it appears as though NAV mode works just fine when on a DME arc driven by the 430; I plan to personally confirm this the next time I'm doing such an approach.

I'd suggest removing the note and replacing it with a discussion of when NAV versus GPSS should be used, and perhaps what differences there are between the two modes. This functional difference is covered reasonably well in the description of the use of APPR versus NAV for a VOR approach.

It would also help with the confusion that NAV and GPSS do exactly the same thing; at least in this case, they do not. I couldn't come up with a reason when you would ever use GPSS instead of NAV, but someone on the COPA list suggested that it is useful when doing a VOR approach with GPS overlay, allowing you to drive the A/P with GPS information while leaving the navigator and CDI in VLOC mode. I haven't confirmed that this is true, but it makes sense.

It would also be useful to cover the APPR function in the GPS section, even if it just repeats the information in the VOR section that the APPR button does not need to be used on a GPS or ILS approach; it's just an indication that the approach and typically the glide slope is armed.

I have a couple of other ideas about the description of FD mode if you are doing a general revision.



Posted By: AviJake
Date Posted: 12 Dec 2013 at 8:08pm
Thanks Bill.    Not sure when the next rev of the Pilot Guide will get pumped out but I did put your note in that folder.

Steve Jacobson

Posted By: GYORC
Date Posted: 26 Oct 2015 at 7:44am
Is an update of the DFC90 manual in sight yet? I would very much apprciate some insight into topics like GPSS vs. NAV modes (is it, or is it not the same?) ... and some other stuff that really needs clarification (can the DFC90 fly DMEarc in NAV mode?)

Cirrus SR22-G2 GTS, Avidyne Entegra, DFC90

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