DFC 90 GS Activation for ILS
Printed From: Avidyne
Category: Avidyne General
Forum Name: DFC90/DFC100 Digital Autopilot
Forum Description: Topics on the Avidyne DFC Digital Autopilots
URL: http://forums.avidyne.com/forum_posts.asp?TID=142
Printed Date: 25 Dec 2024 at 1:58pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: DFC 90 GS Activation for ILS
Posted By: mvitalis
Subject: DFC 90 GS Activation for ILS
Date Posted: 20 Apr 2011 at 11:39am
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I am having difficulty getting ILS GS activation in my recently installed DFC90 in an SR22 G2. I am following the DFC90 Pilot Guide however, it is not explicit with regard to the interactions with the 430W. Specifically, the Pilot Guide discusses the ILS approach (page 4-6) in the context of "Vectors-To-Final" approach without saying whether is it required to select this in the 430W. I never do this as you lose everything prior to the FAF, so I always select an IAF that is appropriate. Secondly, I typically activate a leg once getting vectored (more or less) inbound, usually an intermediate fix between between the FAF and the IAF. However, if I am using HDG (I also tried HDG+NAV) up to this point, and then decide it is now time to arm the DFC90 to capture the localizer, if I press NAV, it turns outbound (!) to the IAF and will not capture the active leg. If I press GPSS, it will capture the active leg, but will not capture the glideslope (although it will arm the GS, however it remains cyan and never turns green). Pressing GS or APPR does not do anything. I am careful to be at the correct altitude and therefore am below the GS. It is not clear to me why, if I activate the leg why the MFD reports the active way point is the IAF and not the intermediate fix that is now the target waypoint of the active leg. This seems to be the underlying problem. Obviously, GPSS is the wrong thing to press, but the only way of capturing the active leg. Since I expect to be vectored to the ILS in almost all cases, how does this problem get solved? Yes, the Primary Nav LSK is set to VLOC1 (as is the 430W) and it is the correct ILS frequency. Maynard |
Replies:
Posted By: jfourrn52
Date Posted: 20 Apr 2011 at 1:02pm
While I don't have all the answers -- I'll take a few guesses for you. First--- If you push only NAV from HDG mode you'll end up in the 45* intercept mode (see pilot guide 3-3 and 3-4 for more detail) Incidentally, I can't think of many times you'd use this but it is a mode that has been on most autopilots since the dawn of time, I'd much rather be in HDG+NAV and control the intercept angle. So you should be using HDG+NAV if being vectored to the intercept. That is the button pushing that should need to be done--- the system should fly heading right up to pretty near the intercept, then turn onto the localizer automatically. It will also at this point go into APPR automatically and arm GS if you are in ALT mode. Just be sure not to arm NAV (that is by pushing HDG+NAV) till you are either cleared to join the final approach course or cleared for the approach. Also, keep an eye on the GS arm-- because you have to be in ALT mode for it to automatically arm, if you are descendning you will have to manually arm the GS. On the other side of that is occasionally you might have a clearance to join the final approach course but not descend. Again you have to watch for the automatic GS arm and be sure to disarm it (by pushing the GS button). Let me know f this make sense--- if not, I'll try again. Also, may I ask where you are located? -Joe |
mvitalis wrote:Posted By: mvitalis
Date Posted: 20 Apr 2011 at 2:44pm
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Thanks for the response Joe. I am at MFR (Medford, OR). I understand what you are saying and it makes sense, except it doesn't work! In fact, I was being vectored by Approach in HDG+NAV when the localizer armed and it turned outbound (!) to the IAF (SAMIE). I tried (several) times to use either HDG then NAV or HDG+NAV while "vectoring" myself, but it consistently turns outbound to the IAF each time, and the MFD reports the "active" waypoint as SAMIE even though I activate the leg from AMASE back to SAMIE. As I mentioned, GPSS correctly turns inbound to AMASE but GPSS won't arm the GS. If I select Vectors to Final in the 430W, then OED becomes the target waypoint and the GS is armed and then activates correctly, but who wants Vectors to Final! The problem seems to be activating the leg rather than going DIRECT to a waypoint (e.g. direct to AMASE), but I don't want to go direct to AMASE, since I'm being vectored to join the localizer somewhere before AMASE (yes, I could cheat, but it shouldn't have to work that way). I've checked this forum and the one at COPA and haven't found anyone else having this problem, perhaps it's the DFC90 I've got ...??? Maynard |
Posted By: jfourrn52
Date Posted: 20 Apr 2011 at 3:12pm
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I'm in Maine-- So I guess going flying together is ruled out! What is got me is that the DFC90 shouldn't care what leg is active in the 430W if you are in the VLOC and NAV is the AP mode. It just responds to the CRS input from your CRS selctor on the PFD and left/right deviations on the localizer. I agree that VTF isn't desirable. So just to be sure--- you are putting your cursor on AMASE then menu-->activate leg---enter---enter right? or (direct direct enter) In that case I'd expect AMASE to be the active waypoint on the MFD. But that shouldn't really matter. Wait---- do you recall what your CRS was on the PFD-- are you sure it was correct? Could it have been that you selected the leg from OED to SAMME giving you a CRS of 320? The first thing the autopilot does upon entering NAV mode is turn to the heading that corresponds to the CRS that is set in the PFD--- then it watches the course deviation and starts to correct. What if for testing-- you go really old school--- forget the 430W flight plan--- just tune the localizer manually, set the CRS yourself. I'm not trying to call your flying into question here... Just throwing out possible ideas! I've got a tentative plan to fly on Friday and play with a video camera. I'll try to get a video of me doing it. I'm sure I've done it your way before as it is just how I like to do it. As far as it being your DFC90 -- I guess anything is possible but everything is so digital that it seems unlikely. -Joe |
Posted By: mvitalis
Date Posted: 20 Apr 2011 at 8:38pm
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Posted By: jfourrn52
Date Posted: 20 Apr 2011 at 11:31pm
I'm still chewing on the rest of your post... but I thought I'd grab this one quickly. While the localizer only projects one course, the pilot or autopilot has to have some idea of what the course is in order to fly it. I'm ALMOST sure the autopilot uses the CRS selector setting as a "home" heading. Once the localizer needle starts to center the autopilot goes into NAV mode. It isn't easy to see this on a localizer because often it happens too fast-- but it turns towards that "home" heading, then it starts to make corrections to track the needle. From 2263.2 miles away (yes, I checked) the only thing that I can think that happened was the following: You selected KMFR ILS 14 with OED as the transition- This made your flight plan: OED SAMIE(IA) AMASE RW14 The course from OED to SAMIE is 320. If you switch to VLOC here--- the 430W can no longer automatically set your course for you. When you select the proper leg in the FPL (SAMIE-AMASE)- your CRS is still going to be wrong. My guess is that the autopilot isn't trying to bring to to SAMIE per say--- it is just turning towards 320 because that is what it expects the course to be (roughly). In the NAV mode I don't think the DFC90 uses anything but heading, CRS, and course deviation to figure out what to do. When Avidyne checks in here, they might be able to give a definitive answer. One more thing to think about---- while in HDG and before capture think: SOURCE- VLOC COURSE- for the ILS 14 (it should be 143) FORCE- good ID on the localizer This might help catch anything that is set improperly. Also-- The Garmin 430W trainer database waaaay out of date so I might be a little off with the waypoint names. I was expecting OSSAJ to be the FAF based on the chart, but the Garmin trainer shows AMASE. |
Posted By: mvitalis
Date Posted: 21 Apr 2011 at 4:06pm
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The transition was SAMIE (not OED) so the whole course should be 014. I did check to make sure that: 1) VLOC1 on the PFD LSK (and the 430W - the Pilot's Guide recommends setting this in the 430 and letting it autodrive the PFD). 2) The correct ILS frequency on the PFD; again driven from the 430W. I will (hopefully) remember to check the CRS and confirm what the MFD thinks the current course is. Although the 430W and the MFD agreed that the leg from SAMIE to AMASE was active (both were purple), the active waypoint in the 430W was AMASE, whereas the waypoint target in the MFD was SAMIE. Thanks for your ongoing help. Maynard |
Posted By: mvitalis
Date Posted: 22 Apr 2011 at 8:10pm
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I flew the ILS 14 MFR approach many times today and got a better handle on what is happening. You were right, the CRS was key. My testing wasn't exhaustive, but it seems that (most of the time), the CRS pointed to the current BRG to the target/initial waypoint when the approach was activated or loaded. If I switched the 430W CDI back to GPS then VLOC it would change to the then current bearing to SAMIE. Once I got "close enough" to the localizer, it would then switch to 143, the correct course for the ILS. Once I had the correct CRS, I could then activate the appropriate leg in the 430W then go from HDG or HDG+NAV to NAV and everything would work normally (i.e. it armed then activated the GS). I don't have a complete handle on which combination of knobs, or where in the approach cycle, the CRS would correct. I would be flying down the approach, then break off, typically before AMASE (the "FAF"), cancel the approach by removing it from the 430, sometimes load a GPS approach just to make sure everything was cleared out, fly using HDG and ALT for a while while I got everything setup and then activated another ILS/SAMIE. I did try using GPSS to fly to SAMIE rather than HDG, then activated the leg from SAMIE to AMASE and hit HDG, but it picked a CRS of 309 out of the air (that wasn't the current bearing to SAMIE), and so I had to start over. I will typically be flying GPSS, then once I get vectored, will be using HDG until the approach will be loaded or activated, then switch to HDG+NAV then NAV. But frankly, until I can repeatedly get the correct CRS corresponding to the ILS, I'm not going to trust this system. Maynard |
Posted By: jfourrn52
Date Posted: 22 Apr 2011 at 11:01pm
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I'll hazard a few more guesses... But first... always remember, once you are in VLOC that the 430W can no longer autoslew the CRS for you. If you select the approach by choosing a IAF, then switch to VLOC, then activate leg--- you are headed down the wrong path... You'd have to set the CRS yourself in this case. A more reliable approach is to choose your IAF, activate the leg you want (I usually choose the something just outside the FAF to the FAF--- the pretty picture will stay up on the MFD for you!) then switch to VLOC. Now the CRS should be correct. Something I see fairly frequently, especially on multiple approaches is not switching the nav source back to GPS between approaches. It is easy to have then have the GPS going one place and the VLOC/NAV going another. If you switch back to GPS between approaches it will be esier to se that you have everything one the same page. Perhaps, on the first day, you stayed in VLOC most of the time-- if this was the case, no matter what you try with the GPS--- your selected CRS would stay put (presumably set incorrectly), confusing both you and the autopilot. This also helps explain why GPSS worked okay for you, as GPSS doesn't use the CRS setting from the PFD. GPSS uses the DTRK, TRK, Deviation and roll steering data from the 430W to fly. I appricate your reflectance to use the system till you fell confident in know exactly what it will do for you and how to get it to do that! -Joe |
Posted By: AviJake
Date Posted: 23 Apr 2011 at 9:42am
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Hi guys, We should be able to wade into this thread when I return on Monday and double check a few things in the lab. Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: jfourrn52
Date Posted: 25 Apr 2011 at 10:53am
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Steve- I'm looking for the page reference defining under what conditions that the GS mode will automatically arm-- the closest I can come is page 4-7 from the DFC90 pilot guide-- the fourth bullet point says "The autopilot will automatically arm the GS vertical mode, retaining the existing vertical mode until capture." But it doesn't say what conditions exists must exist for the GS to arm. Really, it just says what will happen to the existing vertical modes. My understanding is that the autopilot has to be in the APPR mode and also in the ALT mode for the GS to arm automatically. But I can't see where the pilot guide tells me this. Can you help? |
Posted By: AviJake
Date Posted: 25 Apr 2011 at 11:24am
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Hi Maynard, I had a chance to look more closely at your report and verify a few actions in our integration lab. Before I get into that, I’d first like to thank you for your feedback and question set. We do prefer for the professional IPs and trainers to provide instructional guidance and training. I am however, very interesting in ensuring we adequately explain any behaviors you are observing with our equipment and determining if, and where, we can improve our Pilot Guides. While I don’t recall any other field reports of “turning the wrong way” behavior, I will offer up two salient points/observations that I personally experienced during development flight test for the DFC90. The first one is a carry-over from PFD-STec55X-Garmin430 configurations and has the same behavior in DFC90 equipped aircraft. The most common scenario is that you are flying multiple radar patterns during practice instrument work and taking ATC vectors to instrument final. If the pilot is in HDG mode of the autopilot during radar downwind while on ATC vectors and then arms NAV (so in the DFC90, you see HDG in green and NAV in cyan) before the aircraft heading is within 90 degrees of the final approach course value, the Garmin 430 can pick up the localizer signal, and if close enough to the localizer beam, the system will say, “Ahah, I see a strong localizer beam so I will transition from HDG mode to NAV mode and track the localizer beam.”. The issue here is that the PFD/DFC90 logic is such that aircraft heading is taken into account to determine if the system should be tracking the inbound localizer beam or the outbound localizer beam. In this scenario, the approach has been properly loaded and activated in the Garmin 430 but the pilot has elected to arm the approach before being on some 45 deg like dogleg to final or when ATC has cleared you for the approach. For example, I personally experienced a few cases where I tried to “get ahead” of the approach and while still on downwind but getting close to where I thought ATC would turn me to some kind of base leg, I activated the approach in the Garmin and then armed NAV in the autopilot. Then, the Garmin would pick up the localizer beam, I would see the transition from HDG to NAV and the autopilot would turn outbound and track the localizer until I took a manual action. (One other point to consider here is that I intentionally wrote in the Pilot Guide that the recommended time to arm NAV is when ATC has cleared you for the approach. That was intended to deal with the case where ATC either intentionally or unintentionally vectored you across final without explicitly clearing you for the approach so you wouldn’t want the HDG to NAV capture to occur.) The second one is also a carry-over from the PFD-STec55X-Garmin 430 configuration and has the same behavior in DFC90 equipped aircraft. Even if the autoslew (automatic ILS CDI output switch) capability of the Garmin has been turned on, if the pilot elects to manually select VLOC as the Primary Nav source either via the PFD Primary Nav line select key or the “CDI” button on the Garmin 430, prior to the autoslew action taking place, the angle of the last leg in the Garmin prior to the manual VLOC selection will be the value set in the PFD course window. This would have the affect of the autopilot tracking a wrong (but dialed in) course. In this case, the pilot is improperly intervening in the automation sequencing and not setting the desired course in the course window. From the Avidyne perspective: 1. It feels like the tracking outbound localizer signal experience described above may be what you observed on your first sortie; 2. We do want to continue leaving the training up to the professional trainers; 3. We think that if you take advantage of the autoslewing method and automatic transitions of the PFD and autopilot, you should see nominal operation. In other words, the DFC90 did not insert a system-level “bug”, nor do we think your particular unit is somehow misbehaving; 4. I will make some edits to the DFC90 Pilot Guide on its next iteration to include addressing the technique of starting an approach from the IAF and not just taking vectors to final, providing a user tip that covers the premature arming behavior described above, and trying to reinforce the explanation of course behavior if manually intervening in the automation sequencing. 5. If you have other specific pilot guide improvement recommendations, I’d be thrilled to hear them and try to incorporate into the next revision as well. BTW, one note/question from your original 20 April AvidyneLive posting. In it, you wrote, “If I press GPSS, it will capture the active leg, but it will not capture the glideslope (although it will arm the GS, however it remains cyan never turns green).” Per the top of page 4-3 of the DFC90 Pilot Guide, you should never see the GS arm (go cyan) while GPSS is the selected mode. So, are you sure that really happened? We designed the code such that this can’t happen. The reason was principally that we can’t vouch for the same vertical protections in GPSS mode that are guaranteed in non-GPSS modes from the Garmin.) Do you think I’ve correctly understood the problem you were seeing in the airplane? Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: AviJake
Date Posted: 25 Apr 2011 at 11:47am
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Hi Joe, The only criteria for the GS to arm is that a ILS frequency is selected as the Nav freq in the selected Garmin 430. The 430 sends that freq to the PFD which has a look up table from which it knows that frequency is ILS or localizer or something different. If it is an ILS, the system knows it has a glide slope associated with it and will therefore, arm the GS mode. In a DFC90 equipped airplane, GS can transition from armed (cyan) to captured (green) from either below or above glideslope. The capturing-glideslope-from-below scenario is the recommended method since that is more conventional and typically results in a much more stable aircraft and intercept but should a pilot make a benign capture of the glideslope from above, the transition to capture will also occur. ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: mvitalis
Date Posted: 25 Apr 2011 at 2:28pm
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Steve, Thanks very much for your response. I've posted this question here and on the forums at COPA where there are several instructors who responded, but none of whom could answer the question satisfactorily. In fact, there was enough variety in responses that suggested to me that there is considerable confusion about what to do concerning setting up for an approach (so there is an education opportunity!). I also think there is sufficient confusion that there are several suggestion for clarifying your Pilot's Guide, which I'll make in a separate post. I learned, from my testing, and as you confirmed above, that before the localizer is sensed, if VLOC gets activated (either manually or autoslew), then CRS is set to the current bearing to the IAF. As Joe pointed out, I have typically LOADed the approach 30-50 miles out from the airport, depending on how soon I can get the weather, and will then ACTIVATE the approach before picking which leg I'm likely to get vectored to (this isn't always obvious depending on how far out you are and what direction you are approaching the airport from). This potentially causes the initial problem of autoslewing to the IAF rather than some intermediate point on the localizer. But it does bring up the question that I somehow have not yet picked up: When does autoslew occur? When the approach is ACTIVATEd? Does anything happen when the approach is LOADed (presumably not)? If the approach is only LOADed, but not ACTIVATED, what happens (which happens when the pilot is not fully awake)? If out of localizer range and the approach is ACTIVATED and a leg has been selected (say SAMIE -> AMASE), is the bearing to AMASE then set as the CRS or the bearing to SAMIE (the IAF)? The one trick I've learned from all this is that I can manually re-slew (new verb) once the localizer is alive by switching the CDI to GPS, then back to VLOC so as to get the correct CRS loaded. But it still seems to me there is a hole in time where, depending on conditions, the autoslew, if not in localizer range, will set the WRONG CRS. What am I missing? Maynard |
Posted By: jfourrn52
Date Posted: 25 Apr 2011 at 3:10pm
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Maynard- Just to make sure it was made my last post clear-- (this type of information is very difficult to convey in the written form for me!) When you select the leg on the approach-- as long as the nav source is still in GPS-- the autoslew should set the CRS correctly. Switching to VLOC before activating the leg, inhibits autoslew. My understanding of autoslew is it will occur at every waypoint sequencing event IF you are in GPS. Once in VLOC no autoselwing happens! It is all up to you!
If you select a leg SAMIE-AMASE it isn't the bearing the is set--- it is the CRS between those two waypoints (143) that is set. The DTK in the 430W will be 143 and as long as you are still in GPS-- your CRS on the PFD will be too, now is set correctly for the switch (automatic on manual to VLOC) Incidentally, most of these source, course and force kinks have been worked out in the G1000 installs. I understand that R9 also has refined this as well--- just haven't had a chance to fly R9 yet! -Joe |
Posted By: mvitalis
Date Posted: 25 Apr 2011 at 3:31pm
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Steve, Here are some thoughts on the Pilots Guide. Please note that it affects both the EXP5000 PFD guide as well as the DFC90. Firstly, a few quotes which I feel sow confusion: The Avidyne DFC90 Pilot's Guide section 4, page 39 says: This suggests several things which may result in the wrong conclusions. First, VTF is NOT considered appropriate by any instructor I've ever talked with or any student that has a reasonable amount of experience, much less an experienced IFR capable pilot. Second, NAV doesn't capture the localizer signal, it uses what in CRS (which is exactly my problem!). If the localizer is alive when I hit NAV it will follow what is in CRS not the localizer signal! Third, it's not clear what you mean by the "Selected Course window". I now know it is the PFD CRS. Also note, this is the first time (that I can recall) that "front course" has been used in this section - it would be useful to underline this is because you need to set the front course always including the case when a back course approach is flown (OK, this is a very minor point!). Fourth, what happens if the front course in the Selected Course window is not correct? Re-slew? Manually change it? Is there a 3rd option? I would recommend that you remove all mention of VTF and discuss all approaches in the context of real-world scenarios: selecting the most appropriate transition into the approach and optionally selecting and intermediate leg or waypoint along the approach, particularly when/if ACTIVATing versus LOADing the approach may cause confusion with regard to when autoslew happens. Lastly, if the CRS is wrong for any reason, what should the pilot do? Thanks for reading this far. I hope this is useful - it certainly has been useful for me to think through all this stuff on the ground since this process does not work in the air! Maynard |
Posted By: jfourrn52
Date Posted: 27 Apr 2011 at 10:17pm
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Steve- I'm sorry to keep bringing this up but..... from your post a few days ago
This is not the behavior I'm seeing with the DFC90. Imagine the following, the aircraft is in a slow descent in VS such that while presently below the glideslope it will intercept the glideslope before reaching the preselected and armed altitude. The autopilot is in NAV APPR VS ALT. (ahh... color) In this case the GS is not automatically arming. I've tried this a few times and the result is always the aircraft just continues along in VS ALT mode. I understand that all that needs to be done is to arm the GS mode manually. My point is the pilot guide says on 4-7 "automatically arm the GS vertical mode" but what I'm seeing is "automatically arm the GS vertical mode if in the ALT mode". I've got some video of this case--- it was taken from my phone and is quite tough to see what is going on, but should help get my point across. http://www.youtube.com/watch?v=AyJZRVKuIGA - http://www.youtube.com/watch?v=AyJZRVKuIGA Not every intercept works out having the pilot level in ALT mode, perhaps they should--- but it doesn't always work out. Perhaps I didn't ask the right question in my first post. Is what I'm seeing what I should be expecting? Is this what the page 4-7 of the pilot guide saying? I missing something here? Are you sick of me yet?!? -Joe |
Posted By: mvitalis
Date Posted: 28 Apr 2011 at 9:44am
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Joe, I think I've seen this also, but would have to confirm given all the other things I was testing. BTW, thanks for your previous post (which I didn't respond to as I was waiting for Steve to clarify) about CRS for a leg being set to the ILS course (143) and not the bearing to the intermediate waypoint. So do you think I (we?) scared him away, particularly with my (clearly overboard) previous long post about the Pilot Guide corrections? I won't be able to get back in the plane to do more exploration until we return from Machu Picchu/Galapagos as we leave shortly. Maynard |
Posted By: jfourrn52
Date Posted: 28 Apr 2011 at 9:57am
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Your post was fine... Detail is necessary for improvement. I don't think we scared him off so much as I think we move on a whole different time scale than Avidyne. I don't feel it is a this forum is high on the priority list (not that this is a bad thing--- things like keeping FAA certification efforts going might be more important). We are moving on internet time and they are moving on corporate time.
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Posted By: mvitalis
Date Posted: 28 Apr 2011 at 10:07am
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Joe, Yes, good points. Does your testing/experience indicate that:
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Posted By: jfourrn52
Date Posted: 28 Apr 2011 at 11:30am
Autoslew will happen at any GPS leg change if the PFD source is GPS. So when you activate the approach-- yes it will autoslew. Now the question is.... what CRS will it autoslew to? Ahhhhhh, so many choices--- This all assumes that your are being vectored for the intercept. If you activated the IAF, that is to say there is a magenta arrow pointing at the IAF and the moving map is showing a line stating from very near your present position to the IAF, then you will your CRS will be set to whatever the course of the leg is. If you switch to VLOC right now--- you are going to have the wrong CRS (for the approach) the set in the PFD. If you active the the approach (PROC---> Activate Approach?), then go activate the leg from the FAF on back, the CRS will autoslew to the final approach course. You can now switch to VLOC or wait for garmin to do it for you (if all of the conditions are met in time-- lets not go there right now!). If you ONLY activate the leg from the FAF back (staying away from PROC---> Activate Approach?) you have still activated the approach-- and selected the proper leg. The CRS will autoslew to the final approach course and you can now either switch to VLOC or wait for garmin to do it for you down the line. If you activate VTF-- then the CRS will autoslew to the final approach course and again you can now either switch to VLOC or wait for garmin to do it for you down the line. The key is you must be in GPS mode to get autoslew. QUOTE=mvitalis]
(Steve--- I know I'm simplifying TONS of autopilot logic code into a short little blurb--- but do you agree that this is BASICLY how capturing and tracking in NAV mode is done?) CRS definitely get used in the HDG NAV mode--- to demonstrate this--- you can input various CRSs when intercepting a localizer (flying level above the approach altitudes works well for this). Try a CRS seting 15 left of the published inbound CRS and intercept, then break off and try 15 right. The autopilot will command a turn towards the CRS until it "sees" the CDI going off course--- it will then start a turn in the direction of the course deviation (left--right) until it sees the deviation trend reverse. It will then hold that heading until nearly back on course--- then it starts a turn back towards the CRS until the CDI rate of change is null. It continuously and hopefully more precisely (as tracking continues) repeats this. For all the autopilot knows-- you may just have a strong wind blowing you off course. CRS should also be used in the NAV mode--- to demonstrate this--- you can change the CRS while tracking a localizer. The autopilot will command a turn towards the CRS until it "sees" the CDI going off course--- . (I've never tested this demo in the DFC90-- it SHOULD work-- but Avidyne does some pretty fancy stuff with the signal processing so it might not-- but I'd bet lunch at a cheap burger joint that it does) -Joe Clear as mud?
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Posted By: mvitalis
Date Posted: 29 Apr 2011 at 1:12am
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Yes, sometimes writing does not serve the topic best. Being in the same room sharing a white board would be more effective and efficient. However, part of the problem is we're using undefined terms where I suspect we may mean different things. Autoslew is one such term. Garmin doesn't use it and Avidyne only uses it on 1 page each in of their EXP5000 and DFC90 Pilot Guides. From the DFC90: The CDI course is automatically set to the inbound localizerFrom the EXP5000: Avidyne recommends that you set the inbound course using theLastly, the Garmin manual merely allows the operator to set either "automatic or manual ILS switching" without further explanation. So far, no clarity there. My impression (and experience, insofar as my testing has been mostly ILS, with some GPSS) was that "autoslew" was a singular event. What is not clear is several things:
I'm hoping we do get a response from Steve to explain all this as we can test and wonder for quite some time. Having thought about it for a while now, it is not clear to me while the behavior of switching to VLOC before it's time results in selecting the bearing to the IAF was considered by Avidyne as useful. But perhaps that happens as if the localizer is not detected yet, they may not receive the actual ILS course from the 430 so they have to do something else that's not completely useless. Still, the MFD DB has this info, so I'm wondering why that doesn't get used ...?? Maynard Lost in the Mud |
Posted By: AviJake
Date Posted: 29 Apr 2011 at 9:19am
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Guys, You caught me out of the office for a few days again. Let me wade through the recent posts and try to address them all. Depending on the nature of the questions, I may want to verify a few things in the lab before responding. Give me to Monday to try and tackle these. Hopefully, sooner. Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: jfourrn52
Date Posted: 29 Apr 2011 at 9:28am
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Steve- You don't have to apologize.... we know the royal wedding had you all tied up. <grin> |
Posted By: AviJake
Date Posted: 29 Apr 2011 at 9:34am
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You got me. My dog and I woke up a 4am this morning to watch it. We both thought the dress was terrific and we thought Kate's makeup and jewelry were very tasteful. ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: jfourrn52
Date Posted: 29 Apr 2011 at 11:27am
You are right, I never looked it up because I understood what it meant (or at least think I do) but if it isn't defined-- I can't be sure. Also the DFC90 pilot guide doesn't jive with my (personal) definition. First from Webster.. definition #3 http://mw1.merriam-webster.com/dictionary/slew - http://mw1.merriam-webster.com/dictionary/slew ...to turn, twist, or swing about.... so autoslew--- AUTOmatically SLEW. Automaticly-turn, twist, or swing the CRS. Looking back to the "olden days" as my little guys say-- when we had mechanical HSIs we had to manually change the CRS selector at every waypoint change (slew, right?). In fact if you didn't change the CRS within a few seconds--- the GNS430 will flas a messages asking you to. Then electronic HSIs came to be and autoslew became possible. I'm not even sure that when operating in the GPS mode we have a choice to NOT autoslew (unless in the OBS mode) again--- lets not go there today--- if we need to I'll cove that some other day.
Instead of autoslew--- I think this should say ... if GNS430 "ILS CDI selection" is set to Auto... It is mixing two separate events--- the autoslew can happen without the ILS CDI selection being set to auto.
I've never seen a FMS or GPS system that didn't autoslew while in the GPS mode (as oppoped to VLOC) but I guess that Avidyne has to cover it's bases with regard to all GPS systems here. As far as the CDI deflection--- The statement is true--- the deflection (left--right) is driven by the localizer signal without regard to CRS--- For example-- it may give you an "on course" indication. But without knowing the CRS good luck tracking it. Further if you do know the CRS but don't set it in the CRS selector the presentation on the HSI is going to be nearly impossible to interpret.
See page 104-105 of Garmin 430W manual rev. G (or search it for ILS CDI) This will get into it a little more--
When in GPS it happens on every leg--- that is the CRS is automaticly changed by the GPS-- On an ILS it is tough to see because there is only one CRS so it never really "changes" but if a procedure has a bend in it and you are in GPS the CRS will be updated.
At each leg change the 430W computes a DTK (desired track) this is what the CRS needs to be set to to make the HSI "picture" look correct. The autopilot also needs this to have an idea of where it course is so that it can start trying to figure out how to track. CRS really only affects the PFD. This MFD map just displays whatever the GPS sends it (position, track, GS, from waypoint, to waypoint, and upcoming waypoints) on it's own internally (avidyne generated) basemap. The line of where the GPS input start and the MFD generated info starts can be blurry. (must of used the wrong screen cleaner)
Two separate events:
Yes... Autoslews stop-- manual slews (twisting the CDI with fingers) start.
The data sent to the MFD is always GPS and is in no way affected the the GPS/VLOC setting. (that was way too concrete there is always a exception, but i can't think of one) The VLOC reciever in the GNS430 is pretty much stand alone. Except for frequency nonimation, the GPS has no influence over it, including slewing for VLOC CRS. The autoslewing is for GPS--- it just so happens that when we set VLOC the CRS setting from GPS is what we want for the VLOC CRS (usually).
When in VLOC (for an ILS) everyting on the PFDs HSI is from the VLOC receiver. Everything on the MFD is from the GPS, which has an overlay of the procedure in it's database. If a pilot comes from the "old school" they will program the GPS such that it is out of sync with when the pilot is flying the airplane to. So the GPS flight plan will be still trying to take them out to the IAF and to the PT while they are crossing the thershold for landing. Often they are non the wiser, becuase they are in VLOC, with the CRS set (manually), and just keeping the needles centered. The MFD map is all messed up and any GPS derived distances are screwed up too. BUT, the basicly VLOC presentation on the HSI is fine!
Technically, when it comes to autoselew (as I've defined it, right or wrong) the GNS430 is doing all of the CRS selection. Lets say are in GPS and you activate the approach with a IAF--- the 430 is going to want to bring you direct to the IAF--- this results in a CRS being autoslewed to what ever it happens to be to get present position to the IAF. Chances are the it isn't the correct setting for the final approach course. If you switch to VLOC now---- regardless of the presence of the localizer signal, that incorrect CRS is "trapped" in the CRS selector.
The MFD database is ONLY used to make the MFD moving map pretty and for the airport/neatest info that is displayed on the MFD. It is completely independent of the GPS moving maps and nearest functions. You could not have a MFD database and as far as navigation goes, it doesn't matter. That is to say the MFD database just supplies info to improve you situational awareness. This is the curse of integration of cockpits, there fault lines between various systems (VLOC, GPS, PFD, MFD) and it can be difficult to tease out where on starts and the other ends. Also the use of conventional navaids makes this even worse, as the waypoints are cobbed together sometimes to make the conventional work in the GPS world. We end up with GPS waypoints that aren't on the plates, chart fixes (like dme stepdowns) that are only SOMEtimes in the GPS database, CF fixes, etc. In the end when you sit down and figure it out, it isn't too bad, but if the approach wasn't briefed carefully, confusion can rear it's head! RNAV style procedures, eliminate much of this confusion and are in my book, much preferred! (But we still have to be experts at the conventional procedures too...) -Joe
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Posted By: mvitalis
Date Posted: 29 Apr 2011 at 12:05pm
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Steve, Yes, no problem. We look forward to your analysis with great anticipation! Thanks, Maynard |
Posted By: mvitalis
Date Posted: 30 Apr 2011 at 1:03pm
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Joe, Thanks for your detailed reply to my never-ending questions. It does occur to me that there is sufficient complexity here that begs a manual/class that actually explains all this in sufficient detail such that the PIC has some hope of understanding what's going on and why. I do know that (some) Cirrus Certified Instructors do not, so I'm wondering about what training they get (by virtue of the responses I received from them at the COPA forums). You have clearly learned more than the average bear about how all this works; does this come from years of experience in the cockpit of GA/767s as an ATP or are there places/books one may have access to where this stuff can be learned, or what? Frankly, I find unacceptable just having pro-forma instructions from the Pilot Guides and instructors over such a critical area. When things go bump in the night during an approach to minimums in difficult weather, then your life could be at stake. This information needs to be made more available, at least for those of us who want to understand. Maynard (one annoyed pilot!) |
Posted By: jfourrn52
Date Posted: 30 Apr 2011 at 11:36pm
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Maynard- No problem... I love to teach, when teaching I'm forced to think about thinks in ways that I never thought of and that helps me understand even better. I'm not really sure what exactly what Cirrus focuses on in the CSIP training. I'm relatively new to the Cirrus, and not a CSIP <gasp>. I'm a professional mentor pilot and the last couple years I've been very busy in the Meridian and Mustang. A Cirrus moved into the hangar next door and I helped the owner get his Instrument rating in it. Up till now, I didn't have much time for flying other than my full time metor job, so training as a CSIP just didn't make sense financially. It might now that I'm done with my Mustang client as there is a whole lot more Cirrus work than Mustang! My background is older GA equipment (150's 172's and 402's), then RJs for about 10 years (glass cockpit, FMS, good autopilot, but no VNAV or autothorottle-- like a cirrus but at mach .78), then mentoring in glass cockpit aircraft for the last few years. I'm not sure exactly where I learned most of what we have been discussing. One thought is when you get to see many different types of aircraft and avionics, sometimes it helps in the understanding of exactly what box talks to what and why and what data it uses. I'm sure there are some good references out there to help, I just can't think of one right now! Way back in the past I can remember some white papers from Sandel that I thought were just great-- kinda pulling the curtain back on what was talking to what and why. I checked their website and can't find them anymore. Avidyne has somewhat with it's discussion on these forums about some of the DFC control laws (how they solved the spring cartridge/trim challenge if I recall) but the interesting posts haven't been seen for a while. If more information was made available about how and why things work the way the do I for one would be reading it! Not everyone cares about systems detail--- you do and I think that is great. -Joe |
Posted By: AviJake
Date Posted: 02 May 2011 at 12:03pm
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My schedule seems to have served me well with respect to this thread. I just read Joe's 29 Apr, 11:27am post and he seems to have addressed most of Maynard's questions with a fantastic, and very accurate, series of explanations. I'm having some trouble bookkeeping any open questions/issues that still remain. Is it accurate to say they are: 1. Some Pilot Guide enhancements can be made to both the PFD and DFC90 Pilot Guides. Specific examples include, cleaning up the use of CRS/PFD Course/430 Course; cleaning up the explanation of "line select key", clarifying what happens if the pilot manually presses the 430 CDI at various stages of an approach, and maybe a few others. 2. Clarifying when NAV will or will not capture a localizer signal and the impact on the dialed in PFD Course on localizer tracking. 3. Clarifying the triggers for Glide Slope (GS) mode to arm in the DFC90. Do you agree that those are the only open ones or did I miss some others? Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: mvitalis
Date Posted: 02 May 2011 at 2:02pm
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Steve, First of all, thanks for being responsive to these questions. Not all pilots "have" to understand how this works to confidently fly these aircraft, but for those of us who do appreciate your willingness to improve the awareness of how best to use your product. Given the issues with integration across multiple vendors, that just makes it more challenging (for you and for us). However, I do think there are several additional issues to address:
As of right now, I still don't know exactly what the "best" procedure would be to use for an ILS approach assuming I'm in GPSS mode before this all starts. I'm guessing it would go something like this (with additional caveats for what to do when ATC, 1) forgets about you; 2) turns you in within 2NM of the FAF, etc.):
Thanks, Maynard |
Posted By: jfourrn52
Date Posted: 02 May 2011 at 3:41pm
Steve- For now I'll leave the rest to Maynard as he has already covered your questions, except #3. In additions to clarifying the GS triggers, you might also want to somehow impress that if in NAV mode-- the DFC will go to APPR automaticly leading to GS arm. This automatic arm of APPR out of NAV was new to me. In every previous autopilot (from cessna 400 series to the Honneywell Primus 1000 and the GFC700) we used the APPR (APR) mode to control whether or not we were ready for GS intercept. If the controller is withholding the approach clearance for some reason, if we were in NAV we didn't worry about GS capture. With the DFC90 you must really watch and wait for the GS arm--- so you can disarm it. I know that you tried to minimize the button pushing with the DFC--- and you've done a good job, an improvement over the STEC for sure, but this is one step too far IMHO. It used to be simpler-- HDG while being vectored, NAV for the intercept if there was an approach clearance with it, APPR when cleared for the approach--- step down if above glideslope. This is beyond the scope of your question but what the heck.... A more important issue is the ALT buttons interaction with the altitude selector on the PFD. I really wish you'd dump the STEC way of doing it and move on to "The only thing that can change the altitude selector is the pilot twisting the right hand PFD knob" simple, direct, no surprises. All it takes now is one accidental push of the ALT button and confusion and delay springs forth! If the pilot understands what they did then they must reset the altitude selector, which at times (turbulence) can be troublesome (thousands, hundreds, tens-- err no... let see thousands, hundre.. tens.. argghh.... c'mon you've been there!) If the pilot doesn't understand what they did then they must dump the AP and FD (from high automation back to very low) and then start from scratch! If the altitude selector just stayed put--- then if there is an accidental ALT push--- no problem... Just IAS+ALT and you are on your way again. (Sick of me and this issue yet?) -Joe |
Posted By: AviJake
Date Posted: 02 May 2011 at 6:37pm
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< ="utf-8"> Joe,
I hear you on the Alt Preselect thought. We did debate that long and hard and concluded in the end it was a 51-49 kind of thing. For better or worse, we did make a meaningful change with that operation in the R9/DFC100 system. We felt we had more control in that environment and tried to improve things where we could. I think we definitely did that with the FMS/Autopilot interaction and a lot of the confusion that started this thread is virtually eliminated in that system. (Not sick of the issue yet - will try to keep plugging away and address the questions/issues.) Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: AviJake
Date Posted: 02 May 2011 at 6:38pm
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Maynard, Haven't forgotten your latest post - just trying to assemble a complete answer. Thanks for the patience. Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: jfourrn52
Date Posted: 02 May 2011 at 10:54pm
For clarity I've redlined that parts that are not correct by my understanding-- but I could be wrong. Anyone, please feel free to fire away if I'm off here... I've hit the items that seemed like I could be most effective on..... I'll let Steve chime in here and see if I have anything to add. -Joe
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Posted By: AviJake
Date Posted: 03 May 2011 at 7:22pm
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Let's start with a specific topic in this response. Specifically, let me cover the arming and capture of VHF-based GS in this response. To get GS to automatically arm in a DFC90/PFD/430 system, there are 4 conditions that need to be met: 1. PFD Primary Nav must be set to VLOC1 or VLOC2 2. The selected 430 (VLOC1 or VLOC2) must have a valid localizer/ILS frequency dialed in 3. NAV mode on the DFC90 must be either armed (cyan) or engaged (green). [Technically APPR mode must also be armed or engaged but this comes along for free with NAV.] 4. The course value on the PFD must be set to any value that would create a "front course" condition. To get the armed GS to automatically transition to engaged/captured, several more conditions must be met: 5. The glide slope signal must be received and considered valid. 6. The glide slope signal must be within approximately 1 dot of center beam. Note that this can be from below or above - both are equally valid with this autopilot. One important note, you can only have one armed vertical mode. So, if VS was engaged (green) and ALT was armed (cyan), GS won't light up until ALT transitions to engaged (green). Then GS should automatically arm if conditions 1-4 are met. Finally, it is indeed very important to have the proper front course dialed in. I think Joe did a great job explaining when the "autoslewing" will or will not take place. So, the important point is to ensure the proper localizer front course is dialed into the PFD course. This is important because the autopilot is actually trying to track both the dialed in course and the localizer beam. I think Joe used the same analogy in that if the PFD course is not aligned with the localizer course, it's as if a giant crosswind is blowing the airplane off course. The autopilot will attempt to compensate for this by tracking the dialed in course but also seeing the increasing localizer deviation. It will do it's best to solve both solutions but since the localizer signal deviation will be integrated (in a mathematical sense), the error will quickly build to a point where it can't handle it, if the course is meaningfully off from the localizer beam. I will ensure the Pilot Guide is updated accordingly to reflect this behavior. Steve ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: mvitalis
Date Posted: 04 May 2011 at 11:16am
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Steve and Joe, Thank you for the clarification and to Joe for his guidance and patience with me. I think I'm finally getting a clearer picture of what is happening. However, the rationale for having to specify CRS in addition to having a valid localizer is still escaping me. Is CRS just a fallback to make sure we're not going to do something bad? Confirmation that we're doing the right thing (or not)? After all, if ATC forgets about us until after we cross the localizer, turns us back and clears us for the approach, VLOC will have AUTO'd, if (for most pilots), they haven't yet ACTIVATED the approach and now activate it (without selecting a leg), then the wrong CRS will [always] be there. If the pilot does (almost) everything right but decides to manually enter the CRS and does it wrong, then strange things will happen (depending on how far away CRS is from the actual localizer front course). So I can see bad coming from CRS, what good is there? If you require a "front course" to arm the GS, why not require a "front course" to arm NAV instead of having it do something strange. Or highlight the problem by annunciating NAV in yellow. Something to warn the pilot "things are not right!). At the point of localizer detection, the PFD/AP system "knows" there is a difference between CRS and the localizer ...?? And how much of a difference. OK, I'll be quiet(er) now. Maynard |