Why no VSR
Printed From: Avidyne
Category: Avidyne General
Forum Name: IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM
Forum Description: Topics on Avidyne's IFD 5 Series and IFD 4 Series Touch Screen GPS/NAV/COM
URL: http://forums.avidyne.com/forum_posts.asp?TID=938
Printed Date: 18 May 2024 at 1:10am
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: Why no VSR
Posted By: clydeps
Subject: Why no VSR
Date Posted: 17 Jan 2016 at 4:53am
I had a waypoint with a vertical constraint in the flightplan, and a TOD marker on the map, but the VSR was blank. If the IFD calculated a TOD it must have a descent in mind, so why no VSR?
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Replies:
Posted By: DavidBunin
Date Posted: 17 Jan 2016 at 7:05am
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You're looking at the FMS tab's flight plan preview. Go to the MAP tab and the VSR is one of your datablocks. (I'm glad you posted a picture!) Not sure how else I might have known. |
Posted By: oskrypuch
Date Posted: 17 Jan 2016 at 11:36am
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I'm not sure that is it. The OP just has the VSR datablock as a single liner at the top, and it should show the same thing, whether on the MAP or FMS tab, no? I will occasionally see no VSR calculated, with open RNav STARS, even with altitude constraints all in (hoping that 10.2 solves that), previously going direct to IF (vice IAF) would sometimes block the VSR calc. VSR also will not be shown, if it is small. I don't think that any of those apply. The assumption here is that usually you DO see a VSR, correct? Because there are install and version issues that may block a VSR display altogether. * Orest |
Posted By: clydeps
Date Posted: 17 Jan 2016 at 6:51pm
| The VSR datablock on the map page was also blank. It does work some of the time, and indeed started working after I passed the next waypoint. A similar thing happened on an earlier flight yesterday - I had a constraint on the next waypoint after the one I was tracking to and had a VSR. I then went direct-to the next waypoint and the VSR disappeared, even though the target altitude and position were unchanged. |
Posted By: DavidBunin
Date Posted: 18 Jan 2016 at 10:59am
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You are absolutely right, Orest! I didn't even see that. Rats! I thought I had an easy answer. Now I really don't know. I guess at this point the question is what are the flag conditions for the VSR display, or what are the validity limits for VSR? I know I've seen it peg at 3000fpm if I fly over the restriction. I also see it flagged most of the time in cruise. |
Posted By: AviJake
Date Posted: 18 Jan 2016 at 12:51pm
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The reason you're not getting a VSR is because the altitude
constraint is defined as "at or above". Since you're above the
constraint altitude, you've met the constraint and no altitude change is
required. Therefore, there is no VSR. If you changed the constraint
to "at" or "at or below", you would get a VSR value.
Note that an at-or-above constraint in an approach is treated as an "at" for purposes of VSR computation, thus providing vertical speed required to cross each constraint at the lowest legal altitude. In all other kinds of procedures, however, we'll use the specific constraint kind for VSR. ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: clydeps
Date Posted: 18 Jan 2016 at 5:42pm
Steve, thanks for that - it makes sense, but still doesn't match what I actually saw. In the example posted above, the waypoint tracking to is the IA of an approach, so I would have expected VSR guidance based on your comment. Also, if no VSR is computed, how did it come up with a TOD? Here's another example - this is is from the simulator but I saw the same behaviour on the same approach in flight; FPL is YTWB to YBOK with the ILS14 approach selected, via the VOR OK then the locator BMR. BMR has a "not below" 3700' constraint, and I do have VSR displayed:  Now I select Direct To BMR - the VSR disappears but a TOD marker appears. Same vertical constraint, different behaviour.  |
AviJake wrote:Posted By: luchetto
Date Posted: 18 Jan 2016 at 10:13pm
| Clyde doesn't a TOD mark the point FROM which you start a descent. I would expect the VSR to appear once you reach that point. |
Posted By: clydeps
Date Posted: 18 Jan 2016 at 10:18pm
No, you can have a TOD and a VSR at the same time - the VSR shows the vertical speed that would be required to reach your vertical constraint if a descent was started from your current position, the TOD marker shows the point at which the vertical speed required will match what you put in the setup (default is 500fpm.) So as you fly along the VSR updates based on your current position, and watching it is another way of determining how close you are to top of descent. That's how the VSR works when it appears. No problem with it when it's there.
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Posted By: luchetto
Date Posted: 18 Jan 2016 at 10:19pm
| Isn't the point of the TOD also dependent from the preferred VSR set up in the FMS set up menu? |
Posted By: clydeps
Date Posted: 19 Jan 2016 at 12:37am
Yes, I noted that in my previous reply. And that's the point - for the IFD to compute a TOD it has to compare the preferred descent rate with the current vertical speed required and extrapolate along the route. So that's why I don't understand how it can display a TOD if it has not calculated a current VSR, and if it has calculated the VSR, why isn't it displayed?
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Posted By: luchetto
Date Posted: 19 Jan 2016 at 12:53am
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Then I have only one exaplanation: in your first picture OK has no altitude restriction so the VSR is calculated to BMR. In the second picture you are very close to your TOD and you are most probably at an altitude which is very close to your preferred VSR. I have seen in the SIM that you need to move the altitude ruler a bit to get the VSR to display again, there is some tolerance in there in my view. Try your second example again by placing the aircraft further away and select an altitude on the ruler which would require a clear altitude change. |
Posted By: luchetto
Date Posted: 19 Jan 2016 at 1:07am
| Clyde I tried it myself and it clearly showed a VSR. I had the airplane set at 9000 ft with Dct BMR set for the approach. I think it was a coincidence in your case where your altitude and the proximity to the TOD yielded no VSR. I wonder if the VSR would have appeared beyond your TOD. |
Posted By: clydeps
Date Posted: 19 Jan 2016 at 1:13am
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Those two screenshots were taken seconds apart - the altitude was unchanged, the VSR would have been almost the same in the second one. All I did was select BMR and hit direct-to. Exactly the same thing happened in flight on that approach - I don't really care what the simulator does, and in flight "placing the aircraft further away" isn't an option! Steve explained that an "at or above" restriction doesn't necessarily imply any need to descend - and that's perfectly logical - but he also said that on an approach an "at or above" restriction is interpreted as "at". But I've seen in flight and on the simulator that it works as described some of the time but not all the time. There's clearly something different between what is expected to happen and what does happen under some circumstances. All I'm asking for is either a good explanation as to when it should work and when it shouldn't, or if that isn't available then that this be added to the list of bugs (or "characteristics") to be addressed. It's not the most significant issue with the IFDs but it is unexpected behaviour.
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Posted By: AviJake
Date Posted: 19 Jan 2016 at 7:22am
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Ahh yes, we can improve that on the next big round of software updates. It all comes down to how the system recognizes the waypoint in the sequence. If it's inside the procedure side brackets or outside the procedure brackets. Inside the brackets, the VSR datablock is populated, outside it is not in your IAF example. ------------- Steve Jacobson sjacobson@avidyne.com |
Posted By: brou0040
Date Posted: 19 Jan 2016 at 10:15am
AviJake, When you address this, can you do so by fixing the IAF placement rather than allowing VSR to be calculated to an IAF outside the brackets? I've posted other cases where IAF placement is incorrect. See http://forums.avidyne.com/forum_posts.asp?TID=693&KW=IAF&PID=7333&title=kptv-approach-confusion#7333" rel="nofollow - HERE . I'm not sure why my other post hasn't gained traction, in my eyes, it should have created an AD.
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Posted By: clydeps
Date Posted: 19 Jan 2016 at 4:39pm
I suspect that's how it will be fixed - looking again at my example I can see that is exactly what happened - the IAF is still tagged IA but is no longer enclosed in the approach brackets, which explains why it's no longer getting the special treatment for "at or below in an approach". And my original post shows the same on the RNAV approach. I just tested on the simulator and the same thing happens whether Direct-To or Activate Approach is used. My work-around for now will be to change the "at or above" on the IAF to "at".
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Posted By: oskrypuch
Date Posted: 19 Jan 2016 at 4:44pm
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Cool Beans! It sure is nice to have this forum. * Orest |