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Issue with Direct To distance count down

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pburger View Drop Down
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    Posted: 22 Dec 2014 at 12:04am
I had just departed my home airport (TS07) for a lunch run to 11R which is out to the west.  A buddy called me up on the radio and asked if I could go to 1500' and 10 miles and call him from that spot so that he could adjust the sensitivity of our pilot-controlled-lighting.  No problem.  At that time I was on a Direct-to flight plan to 11R.

I decided to do a 'direct to' TS07, so that I could see the distance in the upper right data block. (Yes, I'm sure there are many better ways to do this...)  I hit the Direct key, typed in TS07, hit enter then enter again to activate the direct route.  Keep in mind that TS07 is behind me.  The "Dist" field showed 7.7nm.  I reported 7.7, and told my buddy I'd let him know when I was at 10nm.  I looked again, and the Dist field now showed 7.4nm. What the hell??  I was immediately discombobulated.  I thought I was traveling west, away from the field, but the GPS distance was DECREASING!!  Lucky for me it was VFR, and I knew the area very well.  I looked down at the iPad, and it said 10 nm, so I circled there while my buddy made his adjustments.  I then proceeded WESTBOUND away from TS07, and watched as the Dist to TS07 continue to DECREASE.  I took a picture of the screen with the iPAD next to it.  The iPad shows 14nm, while the IFD 540 shows 6.5nm!!! (The iPad was correct) I then did a Direct-to route to 11R, and continued on my way with nothing abnormal after that.  


I tried duplicating this on the simulator but could not.  The simulator worked just fine.  However, I noticed that the Dist that is displayed in the TO Waypoint datablock is not the direct-line distance, but rather the distance to be flown.  For example, when I did the Direct-to to TS07, it plotted the U-turn on the screen, and the Dist field actually included the distance to fly the turn, rather than the point-to-point distance.  That was not expected, but perhaps that is mentioned in the manual?  Anyway, no matter how you slice it, the distance to a waypoint cannot be less than the direct line distance, so I'm baffled as to what happened during the flight today.

What's going on Steve??





Edited by AviJake - 23 Dec 2014 at 12:17pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2014 at 10:53am
We can't duplicate any of this on hardware after spending all morning trying.

We tried with TS07 as the origin and when not an origin.  We tried every combination we could think of and did not see the problem.  In every case, the distance counted down when it should and counted up when it should.

What did your IFD540 map do during this event?
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2014 at 2:08pm
Steve,

If you look at the picture, you can see that my position is about 2nm outside of the Class B ring both on the iPad and the IFD-540 screen.  So, the 540 knows where I am, but that data field showing the "Dist" to TS07 is INCORRECT.  As I stated, based on my experience with the simulator, I am assuming that the 'Dist' field is the "distance to be flown" to the TO waypoint, not the point-to-point distance.  (I guess it is supposed to be the distance along the magenta line -- I don't like that, but so be it).  I'm going to assume that something went awry in that calculation.

I will set up a Go-Pro in the cockpit with audio, re-fly the same scenario and see if I can get it to screw up again.  I won't have time to do this until the weekend.  

But, the pictures don't lie.  Strange things are afoot at the Circle-K...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2014 at 2:32pm
Okay, we'll wait for the video to try and explain this. 

We've definitely never seen anything like it.     Has anybody else had this kind of issue?
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2014 at 2:38pm
One theory --

Looking at my 540 display, I don't see the magenta line.  I do see the magenta triangle showing the direction to the waypoint (TS07 in this case), but no magenta line.  I think the 540 plotted the course reversal and path to TS07 and painted the magenta line, but I kept flying away from TS07 such that the magenta line went offscreen.

Here's my theory of what happened (pure guesswork here):

I did the "direct to" TS07, and activated it.  The 540 plotted a button-hook turn back to TS07 and calculated the distance from my position, along that curved magenta line, to TS07 and displayed that in the 'Dist' field.  Then, as I continued outbound, perhaps it was just subtracting the distance I was flying (in any direction) from the "distance to be flown" that was calculated when I activated the "direct to"?  If so, that would mean that the 'Dist' field shown in the TO Waypoint datablock is now virtually meaningless.  That's a guess.  I can re-fly this to test my theory.

Now I'm very curious.  I'll try to fly this tonight, weather permitting.  I might not have the go-pro set up, but I'll see if I can duplicate the problem.

EDIT - I can't test this on the simulator, because the simulator follows the magenta line.


Edited by pburger - 22 Dec 2014 at 2:39pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 22 Dec 2014 at 10:29pm
Repeated the problem.  Uploading the video to YouTube now.  Will post link when it's done.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 12:34am
Okay, here's the video:



Note that when I put the iPad in front of the camera, the distance was out of the frame (sorry).  But at 4:51, right after I removed the iPad, you can see that the 'Nearest' datablock in the lower right still has TS07 as the nearest airport, and it shows 6.3nm to TS07 - while at the same time the 'TO Waypoint' datablock was showing 4.9nm to TS07.  Both on the same screen on the IFD-540!  

I really think it has to do with the 'TO waypoint' calculating the course distance, and not the direct-line distance.  I'm going to amend my theory a bit:  I now believe that when it first plots the magenta line with the course reversal turn it calculates the distance to fly along that route, including the turn.  Then as I am flying out beyond that, it probably is figuring some kind of point where I would intercept the magenta line, and the distance shown in the Datablock is from that intercept point to the waypoint.  This seems more likely.  I still think this is very confusing, and I don't think this is explained in the pilot guide.  At least I couldn't find it.  Maybe this is normal for a FMS, but I don't like it at all.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tony Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 12:54am
The video doesn't play, it says "playback on other websites has been disabled by the video owner".  Since there is no link, I can't go to youtube to see it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jhbehrens Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 2:21am
https://www.youtube.com/watch?v=ayCOKFZcuQk&feature=player_embedded
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 7:18am
I modified the video to "allow embedding".  (I'm not a YouTube guru, so I hope this helps)

The more I study this issue, the more I am convinced it is a bug.  The pilot guide clearly states on page 4-21 that the "To Waypoint Information" datablock should show "...distance to current waypoint from present position".  Well, it ain't doing that.  I think the "To Waypoint Information" datablock is calculating it's distance in a similar way as the "Next Waypoint Information" datablock:

The "Next Waypoint Information" datablock shows the "flight plan leg distance for the next waypoint...".  I assume that means it shows the distance, along the flight plan route, from the TO waypoint to the Next waypoint.  That makes sense for the Next Waypoint Information.  It assumes you are going to fly to the TO waypoint.  It tells you how far the Next waypoint is from the TO waypoint.  

I think the "TO Waypoint Information" datablock should show the distance to current waypoint from present position like it says in the pilot guide -- similar to the "Nearest Airport" datablock, which shows "distance to airport from ownship"

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tony Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 8:28am

That's great data, I assume its repeatable since you had the camera all set up to capture it. 

To me it looks like nav was working fine.  You had altitude, heading, and ground speed; but guidance pewked. If you notice in your video, when TS07 was the nearest airport and you continued to fly away, the distance was correctly updated until another airport became closer to your position.   So when guidance pewked the 540 stopped figuring out where to go. 

I wonder what would of happened if you selected a direct to, to a different destination, let the IFD figure out new guidance, and then did another direct to TS07.  I'll bet you that would have probably worked.  I'm guessing that the guidance CSCI didn't like that you selected a direct to from the origin. 

This is normal stuff for a new FMS.  We are fortunate to have a forum like this to get the data back to the design team, and management willing to fix it.  This is going to be an awesome product. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 8:45am
Copy.   Will think harder about this one today and post an update when I have one (that might be a few days).
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote teeth6 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 9:09am
This is probably not totally related to your issue but when you first hit direct to it gave you the distance along the magenta line (not the point to point) as you already said.  I agree this is confusing especially when wanting to know exactly how far you are from the airport.  Along these same lines, I saw a similar issue when I was in a hold with 5 miles legs after a missed approach.  I had intended to fly outbound 5 miles and then start my turn inbound to the fix when the 540 said I was 5 miles from XYZ.  As I passed XYZ to start my outbound leg it said I was 15 miles from it and then starting counting DOWN so (as in the case above on this thread) the further I flew from XYZ, the distance got less.  I am not sure I really like the logic in the box on this one but the explanation from Avidyne was:
That datablock shows remaining leg distance.  A hold is considered a single leg that looks a lot like a racetrack, so the leg distance represents an entire lap and the remaining distance counts down until you cross the hold fix.  If you continue in the hold, then the distance will jump back up when you cross the fix and then start counting down again.
The start of the issue here (with the magenta line and the turn back) sounds similar to what I saw.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 10:13am
teeth6,

So you were already established in the hold, and the legs were set to 5 miles, and the distance reset to the total hold distance as you crossed the fix?  To me, the behavior you described is what I would expect.  Did the distance count to zero as you competed that lap?  Perhaps the datablock title and pilots guide needs to be more clear regarding direct to or along the flight plan distances for these datablocks like they are for the destination block.  The To and Next fields should be along the flight plan, not direct distances.

Avidyne has stated they are going to add a datablock that is the straight line distance to an arbitrary point.  This would be the block that would contain the data you were expecting.  Without more information, I believe this is unrelated to the issue above.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 12:18pm
I've changed the title of the post to be a little more descriptive of the squawk.

Something does appear to be not-quite-right and we're actively looking at it some more in the lab right now.  Will post an update when I have something.
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 12:21pm
teeth6,

That is very interesting.  I don't see the advantage in knowing what the total length of the hold racetrack pattern is.  (well, the only thing might be to calculate fuel remaining, or some such).  If I need to fly a hold with 5nm legs, then I need some reference that tells me how far I am from the fix, PERIOD.  NO EXCEPTIONS.  Not everyone has GPSS that will fly the magenta line for them.  Some of us have to hand fly these things, and need to know when to turn.  We shouldn't have to divide the total "leg distance" by two and then take a little more off for the turns to figure out how far we are from the fix.  What real benefit is it to a pilot to know that he has flown 4 of the 15 miles of the racetrack?  I just need to know how far away from the fix I am right now.  Doesn't SA mean anything anymore?

I'm new to the whole FMS world.  So, maybe this is how it is.  Maybe it's all about flying a magenta line, or more accurately, letting George fly the magenta line.  I'm kinda sorta not liking this.

What about timed legs?  The distance really shouldn't matter, except for SA, which is not a small thing. It looks like I need some more sim time to see how this thing works.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 94S Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 12:44pm
In reply to brou0040 post above, It seems to me that pburger's and teeth6's situations are very related.  When pburger entered the "Direct To" into the IFD it computed the magenta line and distance, just like it would for the hold in teeth6's scenario.  The problem arose when pburger didn't fly the magenta line as the IFD expected he would.  It would be interesting to experiment with teeth6's hold by entering it in the IFD and then not flying it as shown to see how the IFD would handle that.  It seems to me that the "Direct To" algorithm should repeatedly recalculate the direct to solution from the aircraft's current position rather than just calculating the solution once when the "Direct To" function is activated.  Even if you overfly the direct to destination, it should continue to recalculate the solution until told otherwise.

I agree with teeth6 that the straight-line distance to the fix is important as I am putting an IFD 540 in a round dial airplane with a less than stellar auto-pilot.  The along-path distance would also be useful, but for the reasons teeth6 gave, the straight-line seems more important.

David
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Post Options Post Options   Thanks (0) Thanks(0)   Quote teeth6 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 2:08pm
Originally posted by brou0040 brou0040 wrote:

teeth6,

So you were already established in the hold, and the legs were set to 5 miles, and the distance reset to the total hold distance as you crossed the fix?  To me, the behavior you described is what I would expect.  Did the distance count to zero as you competed that lap?  Perhaps the datablock title and pilots guide needs to be more clear regarding direct to or along the flight plan distances for these datablocks like they are for the destination block.  The To and Next fields should be along the flight plan, not direct distances.

Avidyne has stated they are going to add a datablock that is the straight line distance to an arbitrary point.  This would be the block that would contain the data you were expecting.  Without more information, I believe this is unrelated to the issue above.


Yes, the distance did count to zero as I completed that lap but it was very weird to see the distance count DOWN as I flew away from the fix.  For a hold, I really don't see the benefit of knowing the total distance around the racetrack.  To me, this is different than a regular flight plan leg.  I don't mean to compare the 540 to the 430 because it is light years ahead and infinitely better but I did like to be able to see how far from the fix I have flown outbound in a hold so I would know when to turn inbound.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tony Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 4:31pm
I think you guys are confusing the distance to go with the distance to the airport.  Its different.  As we start to move into the Next Gen environment, someday we will have to be ready to do time nav.  This FMS was built around DO-236.  It's not a Garmin.  Its much more sophisticated.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Dec 2014 at 4:56pm
94S, the difference between teeth6 and pburger is that teeth6's machine did what I would have expected it to do from reading the documentation and pburger's did not.  Sure it can be argued either way regarding what is "right" for teeth6's example.  When flying shorter legs, do you want that thing constantly chiming - maybe?  Would teeth6's readout have been in error had he flown away from the magenta line?  Maybe, that would be tied to pburgers issue, but he was describing wishing a hold was broken into multiple sections rather than a single leg.

It sounds like what you guys are asking for is to have a hold broken down into individual segments for each part of a hold - I think that would be an improvement, but I'm not sure I would have considered an issue until I read this post.  Making that change may introduce new issues such as the next leg being a previous leg in the flight plan as you are about to begin another lap.

What I would suggest is that when you are in a hold, that a pop up readout show up somewhere on the screen such as the bottom left where the continue/exit hold button is just above the weather label, that is the distance readout and the name of the hold fix.  I know that there is a future datablock that will give straight line distance to a point, but I'm not sure I'm going to want that as one of my normal datablocks and I don't want to have to change my setup as I'm entering / exiting a hold.

pburger, I'm jealous of you being new to the FMS world, someday I'll join you.  Until then, I'm also without GPSS and am still doing SA the old fashioned way...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TogaDriver Quote  Post ReplyReply Direct Link To This Post Posted: 31 Jan 2015 at 9:35pm
I just saw this video.  It jibs with some weird behavior I noticed recently with my newly installed IFD540.  I noted this incorrect distance also populates my Aspen's next waypoint data block too.  In the soup I'm trained to use the Aspen info as primary.

If I am on a flight plan and then am vectored by ATC for traffic, etc, I wonder if the distance would no longer be accurate until a leg was re-intercepted, or until a Direct-To was executed?

Avi-Steve, what is the status of this issue with the development team?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2015 at 11:37am
I'm not sure I understand the issue/concern but if IFD540 datablocks are the question here, there are a few subtlety different datablocks.  A snippet from the Pilot Guide:

To Waypoint Information*

To Waypoint Information no Fuel.jpg

To Waypoint Information with Fuel.jpg

To waypoint identifier, desired track to current waypoint along flight plan route, distance to current waypoint from present position, estimated remaining fuel at the current waypoint (if a fuel flow system is connected), and estimated time enroute to the current waypoint in HH:MM. The data will be displayed in magenta. (4 or 5 lines depending on whether a fuel flow system is connected)

Next Waypoint Information

Next Waypoint Information no Fuel.jpg

Next Waypoint Information with Fuel.jpg

Next waypoint identifier (the next leg of the flight plan, not the current leg), desired track to next waypoint along flight plan route, flight plan leg distance for the next waypoint, estimated remaining fuel at the next waypoint (if a fuel flow system is connected), and estimated time enroute of the next leg in HH:MM.  (4 or 5 lines depending on whether a fuel flow system is connected)

Dest. Along Track Info.

Dest. Along Track Info. no Fuel.jpg

Dest. Along Track Info. with Fuel.jpg

Destination identifier, total distance to destination along the remaining flight plan legs, estimated fuel at destination (if fuel flow installed) and estimated time enroute to the destination in HH:MM format (Z or LCL units dependent on User Options page selection).(3 or 4 lines)

Destination Direct Info*

Destination Direct Info..jpg

Destination identifier, bearing to destination from present position and distance (in NM) to destination from present position. (3 lines)

p
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2015 at 11:49am
I've been waiting to see this post updated.  This seems like a primary navigation issue that should be a very high priority, yet it's been silent for over a month - disappointing, not even a status of we're still working it.

It seems like this is something that anybody with a 540 could test in their airplane (unable to test on the sim since it follows the magenta line).  It would be nice if others chimed in with this test case and reported their findings.

After confirming the same behavior, I'd also try hitting direct to the same waypoint again and seeing if it updates the calculated distance to something reasonable again, then continues it's erroneous behavior.

Also,  what happens if you let it count down for awhile while flying away from the magenta line for a few miles, then turning inbound.  Does it continue counting down from the value it had, does it update to a correct value?  This would be useful troubleshooting the bug.

---------------

AviJake, any thoughts on pop-up box with distance to the fix while in a hold so that you don't have to modify your datablocks when entering / exiting a hold similar to the continue / exit hold button?


Edited by brou0040 - 01 Feb 2015 at 11:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2015 at 11:52am
Originally posted by AviJake AviJake wrote:

I'm not sure I understand the issue/concern but if IFD540 datablocks are the question here, there are a few subtlety different datablocks.  A snippet from the Pilot Guide:

AviJake, Can you state which of the above boxes you believe could provide the information shown in the video?  Maybe I'm completely confused, but I can't see any of them doing this.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2015 at 11:59am
I'll pipe in to address those questions on Monday - I'm not able to do the appropriate level of homework on this until Monday, presuming the weather permits travel.
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MysticCobra Quote  Post ReplyReply Direct Link To This Post Posted: 01 Feb 2015 at 6:35pm
Originally posted by AviJake AviJake wrote:

I'm not sure I understand the issue/concern ...

The issue/concern is the same one you acknowledged on Dec 23:

Originally posted by AviJake AviJake wrote:

I've changed the title of the post to be a little more descriptive of the squawk.

Something does appear to be not-quite-right and we're actively looking at it some more in the lab right now.  Will post an update when I have something.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 12:04am
....not sure you understand the issue/concern??  Seriously?

I'm dissappointed, Steve.  I'm the one who posted the video.  Since that time I have pretty much figured out how the distance field in the "TO Waypoint" datablock operates, and it is NOT in line with what the manual says, and not in line with what I would expect.

You clearly indicated that Avidyne was looking at this and would report back.  Based on your recent post, it sounds like no one is even looking at this - is that correct?

As you point out in your recent post, the manual says the "TO Datablock" shows distance to current waypoint from present position.  THE IFD-540 IS NOT DOING THAT!!!

I believe it is showing one of the following two things, depending on the plane's current position:
  1. If currently on the courseline, then it will show the distance to the current waypoint from present position ALONG THE PLOTTED COURSELINE (magenta line).
  2. If currently off of the courseline, then it will show the distance to the current waypoint from the nearest intercept point of the courseline ALONG THE PLOTTED COURSELINE (magenta line).

Once I get my plane back I will be happy to video a scenario where I am 10 or 20 nm from the current waypoint, and the IFD-540 will show me <1nm away in the "TO datablock".

I would also be happy if Avidyne took this issue seriously, as we were all led to believe they did.

Even if the issue of the off-course distance somehow gets changed, I really don't like the idea that the distance in the TO Datablock is "ALONG THE COURSELINE".  The scenario presented about flying a holding pattern really illustrates to me that this information is pretty much useless to the pilot flying the holding pattern.  As I stated in an earlier post, I need to know how far I am from the fix, not how far I have left to fly in the racetrack.  I suspect that Avidyne may not ever change this, so I would like to request the following:

FEATURE REQUEST:  A datablock called "TO Waypoint Direct Info" that shows the following:

  1. TO Waypoint identifier
  2. bearing to TO Waypoint from present position and
  3. distance (in NM) to TO Waypoint from present position. 
(3 lines)

The above datablock would be similar to the "Destination Direct Info" datablock, but would use the TO Waypoint instead of the Destination.  You might use a color other than magenta to differentiate it from the standard "TO Waypoint" datablock.

Now, THAT would be some useful information, especially if I was off of the courseline.


Edited by pburger - 02 Feb 2015 at 6:50am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Royski Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 10:27am
I'm not sure if it's the same problem, but with my 540 I've seen the datablocks for Nearest and Destination airports show different distances to the same airport.  I took a photo with them off by 0.1 miles but I've seem them off my as much as, I think, 0.4 miles.




Edited by Royski - 02 Feb 2015 at 10:35am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 11:09am
That's interesting, Royski.

Looking at the Destination datablock on your screen, it is clearly the "Destination Direct Info" datablock as shown in the manual on page 4-22.  I would ASSUME that would be the DIRECT distance.  There is another "Dest. Along Track Info." datablock that shows distance along the flight legs, but you clearly have the "Destination Direct Info" block on your screen.

Avidyne - please check into this!!    This is GPS, it should be dead nuts on.  There is no "close enough"  Either fix the calcs, or explain what information is being displayed.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 1:21pm
I would guess that the difference is the precise destination point at the airport, the airport center versus the arrival end of the runway, or something like that.

* Orest

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tony Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 2:52pm
If I remember correctly, nav was working just fine.  The airplane knew where it was, however the guidance stopped working.  The distance to the next waypoint didn't update and so the datablock froze.
 
I thought this was a rather interesting problem. 


Edited by tony - 02 Feb 2015 at 2:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 4:50pm
Originally posted by oskrypuch oskrypuch wrote:

I would guess that the difference is the precise destination point at the airport, the airport center versus the arrival end of the runway, or something like that.

* Orest


I would doubt that.  How the heck does the box know which runway you're going to?  I would think it uses the reference point of the airport in all cases, but maybe not.  In any event, an explanation is warranted.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 4:52pm
An explanation will have to wait another day or two.   No ability to get to lab and check out today due to snowstorm.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 02 Feb 2015 at 7:58pm
My guess at the difference between the Direct To and Nearest fields would be the update rate of the nearest field.  I thought this was discussed earlier that the Nearest field is not updated at a very high rate.  My guess is that anything used for nav is at a higher rate/priority and anything used for SA is at a lower rate/priority.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Royski Quote  Post ReplyReply Direct Link To This Post Posted: 03 Feb 2015 at 3:45pm
Thanks, I'm pretty sure the different update rate explains what I observed.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 04 Feb 2015 at 4:41pm
Still on my to-do list but haven't come up for air yet to hit this one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 9:21am
Originally posted by pburger pburger wrote:

Once I get my plane back I will be happy to video a scenario where I am 10 or 20 nm from the current waypoint, and the IFD-540 will show me <1nm away in the "TO datablock".

As promised, here is a video showing a scenario where I am approximately 10nm from the TO waypoint, but the "TO Waypoint" datablock shows me at 0.0nm from the waypoint.  Yes, I am not on the magenta line, but I will re-state my point that when I am NOT on course is when I need to know where I am exactly!  This data presentation is confusing and dangerous.

The areas of interest on the video are the TO Waypoint datablock in the upper right (TS07), and the Destination Direct datablock, which is a little further down.  Also, you can see the magenta line on the screen, with the actual position of the airplane about 10 miles north.

At 00:35, you will see that I am 9.6 nm north of the TO waypoint, but the 'TO Waypoint' datablock shows 0.0nm!!  The data displayed was exactly what I expected, because it is working as I described in my Feb 1 post of this thread.  

I believe that this presentation in the TO Waypoint datablock is dangerous and should be modified somehow to present better, less confusing information when off course.  I really don't want someone to hit a mountain.

I also want to repeat my request for a new datablock called the "TO Waypoint DIRECT" datablock which would show the TO waypoint, the Bearing TO, and the Direct distance to.  No curved paths, or any of that, just the bearing and distance in a similar fashion to the Destintation Direct datablock.  If I had that datablock, I would put it in the upper right corner and I would forget about the current "TO Waypoint" datablock altogether.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 11:01am
Yup, absolutely broken.  No misunderstanding of datafields should cause this.  Nearing the 8 week mark from when this was recognized as an issue and still no explanation...  A day or two has also passed.

I think at this point, we should be able to expect an explanation of what is causing this and a plan to address it.  I understand any software change will be down the road, but it should at least be getting some attention.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 11:37am
Curious ...

When you see this behavior, what happens if you recompute the "direct to" route? Does the TO value then correct?

Does this ONLY occur in situations where you are using a "direct to" construct?

It seems to be giving you the distance along the course line, from the course point, from which you are abeam the currently plotted route.

The manual description should probably be updated to reflect this as being along the course line, if that is the intent.

But the other observation I'd make is that it seems to be an unusual situation, and perhaps why this situation was not noticed. IOW, if you hit direct to somewhere, and then fly substantially off the plotted route, would you not hit direct to again if you wished to make use of guidance? If you didn't, then you are creating an ambivalent/undefined situation for the navigation computation-- assuming that the TO waypoint value is meant to be along the course line. 

* Orest



Edited by oskrypuch - 15 Feb 2015 at 12:53pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TogaDriver Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 11:56am
I believe the "classic" behavior of the Garmin 4/500 series is to calculate the distance to the next waypoint regardless of whether you are on the track or not.  This is beneficial for situations when you approaching an airport, either on D-> or as a leg waypoint, and want to announce your distance to the airport.

If I am maneuvering VFR to the 45, for instance, I am often one or more miles off from the original track. Glancing at the data block lets me announce my distance accurately.  Having to mash the D->, ENT, ENT, sequence over and over again is an unsafe distraction down low in the airport environment.

My opinion:  This is a critical bug and needs to be escalated to the next release. Obviously, it goes below bugs that actually crash the box, of course.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote oskrypuch Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 12:44pm
Sure, on approach using a lot of "direct to" is generally a bad idea, other than for the IAF/IF. And having to execute a "direct to" to find a distance alone, is obviously rather clumsy. But in the discussion above there was no approach involved, and the "direct to" was the method of navigating to the airport.

On approach I am often referring to the "direct to destination" datablock. I really like it, and use it often.

The range rings will help with this as well, what would really be nice is a FIX page that you could draw range rings and radials about arbitrary waypoints, including the destination -- that provides very powerful situational awareness. 


But, not to side track the discussion here. Based on the other posts here (I've not actually tried to test this in the air), once it is all confirmed it would seem reasonable that either the documentation needs to be amended and amplified, or perhaps a second type of (DIRECT) TO WAYPOINT data block needs be added, or in time, both.

* Orest






Edited by oskrypuch - 15 Feb 2015 at 12:49pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote brou0040 Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 1:46pm
They are going to add a direct to data block.  That can solve part of this issue, but there is still an issue.  The counter should never count to zero unless you are over the fix.  It shouldn't matter if you hit direct to again, if it's calculating along the magenta line, or whatever.  If the datablock is calculating along the flight path, then it should include the distance to reintercept the magenta line, then fly to the waypoint along the magenta line.  If you fly perpendicular to the point (closest approach), the distance should never go to less than the direct to distance.

Edited by brou0040 - 15 Feb 2015 at 1:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 1:54pm
I am currently airborne on JetBlue heading back to the office and will engage more directly this week. I will say that I absolutely dispute the assertions that this is a critical bug or causing dangerous conditions. I take solace in the passion that a lot of you have on this topic, the product, and aviation safety in general. I will provide a more thoughtful analysis of this issue in the coming days. (I am scheduled for jury duty on Tues so I might be NORDO then)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2015 at 8:39pm
Although Avidyne may not want to hear this, I think this is a case of WWGD?  A large percentage of us have been flying behind Garmins for the last 10 years or more.  I had a GNC-300XL, but I checked with my 430 buddies, and they confirm that when they look at their distance to waypoint they see the direct distance, no matter if they are on the courseline or not.  That's how my GNC-300XL worked, and it was INTUITIVE.  If I've been vectored off the planned path, or if I've deviated for weather, or whatever, I would like to be able to look at the distance and see how far away I am from the waypoint.  It seems pretty simple and straightforward to me.  I shouldn't have to know some esoteric secret about what the distance really means (well, you see, this here unit is an Avidyne, and well, uh, if you're not on the magenta line, then the distance shown to the waypoint isn't really the distance to the waypoint per se, you see... ).  To paraphrase a former president, "I guess it depends on what your definition of "distance" is."  I do think this could lead to some serious confusion, and if you're in the clouds and aren't aware of the "secret" then I could see someone making a bad decision based on data they don't understand.

This all started when my buddy asked me to fly 10 nm from the airport.  I hit Direct-TO the airport so that I could monitor the distance, as I have done many, many times in similar situations in the past with my Garmin.  This is when I noticed the distance counting down.  Although it was a clear day, and I knew the area well, I was really freaked out for a minute or two.  I was wondering how I got turned around 180 degrees.  Once I looked at the ground and realized where I was, I realized quickly that the box was not acting as I expected it to.  If I was in the clouds when this happened, I'm not sure how long it would've taken me to figure it out, especially if I didn't have a secondary GPS to cross-check against.  Say what you will, I DO NOT WANT THE "TO Waypoint" DATABLOCK ON MY SCREEN.  I would rather have the "TO Waypoint DIRECT" block which I have requested.  That would be much more useful to me.  I hope Avidyne will respond to that request one way or another. 

Orest - Yes, this was demonstrated with a Direct-TO, but I've got to assume it will behave the same way any time you depart the magenta line, whether or not the TO waypoint is the result of a Direct-To or just the next waypoint in the flight plan.  Just telling someone to press direct-to repeatedly is not a solution.   And to suggest changing the documentation as a solution to this confusing distance calculation?  Really?  I seriously hope Avidyne doesn't think that it's okay to show a 0 distance to a waypoint that you are 10 nm away from (or 100 nm, or whatever).  That's just silly.  No one I know who has seen this first-hand thinks it's right.  





Edited by pburger - 15 Feb 2015 at 8:40pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PA20Pacer Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 8:55am
It seems as though the issue described in this thread is not so much a bug as a necessary consequence of the fact that the datablock in question is intended to show the distance to the destination along the course line in the flight plan. If you are not on the course line, then some sort of decision must be made about how to calculate the distance displayed. It has been suggested a distance to intercept the course be added, but that begs the question of where the course is to be intercepted.

When I have entered a flight plan for a long trip that includes some doglegs, I have often wished for a display that showed the distance to destination along the flight plan route.

I have also used "Direct To" in the past on other GPS units to give me the distance to a point when maneuvering in an area, such as when practicing formation flying. Obviously, with the IFD540, using "Direct To" and monitoring the distance to the destination waypoint is not the correct way to get the desired information. 

I have not used the IFD540 enough to have a strong opinion, but this does not seem like a safety issue to me as long as the behaviour is clearly described and understood. 

Regards,

Bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pburger Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 9:47am
Bob,

There is a datablock that shows distance to destination along the flight plan route.  It's called the "Destination along track" datablock.  That datablock is available and useful.  It helps with overall flight planning for time and fuel management.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote PA20Pacer Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 10:58am
I will anxiously await Steve's analysis of the motivation for this design element. As I said, I do not have much experience with the IFD540, so I do not have a strong personal opinion about this particular issue. 

Regards,

Bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 4:14pm
Had the chance to finally look at pburger's original post and subsequent updates in enough detail to formulate a real response.

1.   I have an error in my Pilot Guide description of the distance field in the To Waypoint datablock description.   I erroneously wrote it was "distance to current waypoint from present position" when really it's distance to current waypoint along track.  More precisely, it's remaining distance along the path assuming the aircraft were on the path.  I've updated the Release 10.1 version of the Pilot Guide to reflect that correction.

2.  The system does not have a bug - it is operating per design.  I'm sure there are those will argue they don't like the design or the design should change and that will be a fun debate to have.  It is using big iron FMS logic.   As implemented, the distance remaining is measured from a point called the "along track normal" (ATN) and that point represents where the aircraft is supposed to be on the flight plan.  We've put together a set of slides with a bunch of annotated screenshots showing the behavior and how the ATN is computed.  From a philosophical perspective, the system is expecting you to fly the path - it is not designed for you to create a FMS path, then intentionally not use it. Of course that happens in real life and then you have to think about all the cases which we have and still concluded to design it this way.   For example, if we didn't design it this way, what distance would you present in the To Waypoint distance field when flying a DME arc as part of an approach?  Etc, etc, etc.  Use this link to check it out if interested:  


3. I agree that it is operationally very useful to have some easy means of knowing your direct distance (no button hook, no ATN, etc) to a waypoint.   Towards those ends, we are going to create two new types of datablock options for folks to pick if they want.   We will add the "Active Waypoint Direct Info" datablock which will contain the active waypoint identifier, present position bearing to that active waypoint, and present position direct distance to that waypoint.   We will also add the "Direct Distance to Active Waypoint" datablock which will contain the active waypoint identifier and present position direct distance to that waypoint.  Those two new datablock adds will come shortly after Release 10.1.0.0.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TogaDriver Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 6:53pm
Steve,  thanks for the math.  At least we all now know that the IFD is behaving as designed for this data-block calculation, and how, if not exactly why (DME Arc excepted).  It does make sense that you'd want to calculate the time along the course and the box really can't know when the course is going to be abandoned.  

I only wish the ATC universe were ideal and we never got vectored.  But, until then, I really do like to know how far I am (physically) from the next waypoint so AWDI and DDAW (sounds like a stuttering frenchman) will be much appreciated.  Perhaps another way to skin that cat would be a LSK that could toggle the calculation from ATN to DWP (Direct Way Point).  That way we could fly happily along the predicted path until ATC throws us a strange vector, or we need to vector ourselves for an alternate approach. That might not be as obvious as a unique data block but would be easier to use on the fly.

I, like many other IFD converts, am having to unlearn some of the oddness that Garmin inflicted on us with their trusty 4/500s.  Perhaps the next webinar could be on this topic:

12 Steps to the Avidyne Way for recovering Garmin Users
Topic 1:  Which Way is Home and How Far Is It?
...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote teeth6 Quote  Post ReplyReply Direct Link To This Post Posted: 16 Feb 2015 at 7:03pm
The only thing I still don't understand is how pburger got a distance of 0.0 to the waypoint when he was 10 miles away.  Under either scenario (distance direct to waypoint) or with the ATN that Steve described, I'm not sure how the IFD came up with a distance of zero.  Would you explain that.? I'm not trying to push the issue or complain but rather just want to understand how the box presently is functioning.  Thanks
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