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Unable to close “Gap in route” arrival and app

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eloigorri View Drop Down
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    Posted: 16 Sep 2021 at 7:06am
Hoping to learn form your collective wisdom. ;-)

I am slowly getting to grips with all the functionality available via the IFD550 I recently installed and I am enjoying the learning experience as I slowly understand the buttonology and FMS architecture.

I recently came across an oddity on an actual flight which I am sure is just fat finger trouble on my part, but I could not see how to correct it.

Firstly, full disclosure I know the problem is rooted in how my authority/Jeppesen have coded the overlap between the Nakon3A arrival and ILS Z RW21R into VTBD but this occurs often over here in Asia so I want to find out the implications and how to manage the IFD when it happens.

If you see the Nakon3A arrival, it ends in AROKA than BD111 WP’s.


If you look at the actual ILS Z RW21R approach that connects to this, it duplicates the same two WP’s. AROKA being the IAF, and BD111 the IF.


When the arrival and approach are loaded into the IFD, you get this round robin that merrily takes you back the way you came due to this overlap.



This also used to happen in my old GNS units, and I learnt to delete AROKA and BD111 from the end of the arrival to stop this problem. After deleting AROKA and BD111 from the arrival section the IFD still maintains “Gap in route” error with no way to connect back to BD114 the last remaining WP of the arrival, and so to get around that I manually jumped past the gap by going direct to AROKA. Is this the only solution?


Cheers - E


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chflyer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chflyer Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 9:31am
You might want to check in with pilotsafety.org. Gary Reeves has some interesting videos and courses specifically for mastering the Avidyne units. I'm not certain, but my recollection is that this particular case is covered. I don't know if it is in one his free videos or the Avidyne course. I believe it has something to do with the sequence that the route is built. You've reminded me that it's time for me to also take a look at his videos again. ;-)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 10:41am

I suspect that you deleted AROKA from the arrival first and then BD111.  There are a few software-related reasons that the FMS wants to keep the first leg of the approach (AROKA) intact.  So, when you delete AROKA from the arrival and then delete BD111, the FMS inserts the gap.  Deletion of that gap would require insertion of a direct between BD114 and AROKA, but the FMS assumes that an arrival is followed immediately by an approach, so that's why you can't close that gap.

However, if you only delete BD111 from the arrival, then you end up with AROKA as the last leg of the arrival, followed by AROKA as the first leg of the approach.  The FMS notices this and doesn't insert the gap.



In 10.3, this will look slightly different because you'll actually see both legs.  When the aircraft reaches AROKA, the FMS will sequence both of them and BD111 will be the active leg.  There were a couple of reasons for this change.  First, the old method of combining the legs at the boundary betweeen the arrival and the approach could cause some ambiguity in subsequent edits because the FMS couldn't know whether the pilot wanted the combined waypoint to be part of the arrival or part of the approach.  Second, the new method allows the pilot to recognize the situation when a common waypoint has differing altitude constraints.  In the picture below, AROKA has an "at or below 5000" constraint, so there's no gap.  However, if the constraints were different, there would be a gap between the two instances of AROKA.  The pilot would then be able to recognize the issue and resolve the issue, likely by changing the constraint on one of the legs.





Edited by AviSteve - 16 Sep 2021 at 10:42am
Steve Lindsley
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmtidler Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 11:37am

Short answer: no, this is not the only solution to this arrival issue. 

Since I cannot find a similar example to test in the North American IFD database, I also assume that the IFD will not let you delete BD111 on the arrival without first deleting AROKA on arrival. With this in mind, I’m not aware of any solutions that would eliminate manually intervening to get the IFD navigating on the other side of the persistent gap between the arrival and approach.

Long answer: IMO, your technique works only because the arrival course doesn’t change between DOGVA and AROKA. If you are assigned the ENUU3A transition, your method of solution may not work nearly as well.

My take; you may want to consider doing nothing with the arrival and approach routing as it goes into the IFD leaving both the gap and overlapping routing. Once the aircraft crosses AROKA on the arrival routing, perform a Activate Leg to the BD111 waypoint on the approach side of the gap. This preserves the arrival and overlapping approach routing all the way and will work for any transition used on this arrival. Your example technique actually loses the arrival routing between BD114 and AROKA but works because the arrival course does not change at BD114. With only seven miles between AROKA and BD111, the IFD will probably be reminding you of the gap ahead before you even get to AROKA. The downside of this technique is that before the gap, the IFD will have an extra 14 miles of routing built into it; therefore, along track distance to destination, ETA at destination, and fuel at destination will reflect the extra mileage until the active waypoint is sequenced across the gap.



Edited by dmtidler - 16 Sep 2021 at 11:39am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote eloigorri Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 11:56am
Many thanks to you all for the detailed replies.

@chflyer – Thanks for the pointer to pilotsafety.org.  Looks like there is some very useful knowledge in there. The free video on gaps does cover a similar scenario, but Gary’s solution of loading the IAF as a wp before loading the destination/procedures does not work for my particular case.

@aviSteve. Correct, I did indeed delete AROKA first followed by BD111 on the arrival, and trying your suggestion of only deleting BD111 on the arrival using the 10.3 simulator works as you described.   I will try that technique on my actual IFD unit which is running 10.2.6.1 to see if it works there as well, if not @dmtidler’s suggestion is almost what I ended up doing today during the flight.  It sounds like v10.3 will handle it better moving forward.

Cheers - E

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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmtidler Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 1:09pm
Originally posted by AviSteve AviSteve wrote:

I suspect that you deleted AROKA from the arrival first and then BD111.  There are a few software-related reasons that the FMS wants to keep the first leg of the approach (AROKA) intact.  So, when you delete AROKA from the arrival and then delete BD111, the FMS inserts the gap.  Deletion of that gap would require insertion of a direct between BD114 and AROKA, but the FMS assumes that an arrival is followed immediately by an approach, so that's why you can't close that gap.

However, if you only delete BD111 from the arrival, then you end up with AROKA as the last leg of the arrival, followed by AROKA as the first leg of the approach.  The FMS notices this and doesn't insert the gap.



In 10.3, this will look slightly different because you'll actually see both legs.  When the aircraft reaches AROKA, the FMS will sequence both of them and BD111 will be the active leg.  There were a couple of reasons for this change.  First, the old method of combining the legs at the boundary betweeen the arrival and the approach could cause some ambiguity in subsequent edits because the FMS couldn't know whether the pilot wanted the combined waypoint to be part of the arrival or part of the approach.  Second, the new method allows the pilot to recognize the situation when a common waypoint has differing altitude constraints.  In the picture below, AROKA has an "at or below 5000" constraint, so there's no gap.  However, if the constraints were different, there would be a gap between the two instances of AROKA.  The pilot would then be able to recognize the issue and resolve the issue, likely by changing the constraint on one of the legs.



Thanks! 

I had made an erroneous assumption that deleting BD111 on the arrival hadn't worked; hence the specific order of deleting AROKA before BD111. I could not come up with a North American example to test.
   
I saw the format change playing around with the updated IFD Trainer app and was going to ask about it. 

BTW - I cannot get the updated IFD Trainer to show any charts. The AUX-Databases Status indicates charts are not installed; however, going through the Databases Update last night appeared to have downloaded the charts effective 9/17 with no effect. My IFD100 now indicates charts effective 9/17 are installed after the IFD Trainer update attempt.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 16 Sep 2021 at 2:21pm
Originally posted by dmtidler dmtidler wrote:

BTW - I cannot get the updated IFD Trainer to show any charts. The AUX-Databases Status indicates charts are not installed; however, going through the Databases Update last night appeared to have downloaded the charts effective 9/17 with no effect. My IFD100 now indicates charts effective 9/17 are installed after the IFD Trainer update attempt.
I moved this to the 10.3 trainer thread...
Steve Lindsley
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Post Options Post Options   Thanks (0) Thanks(0)   Quote eloigorri Quote  Post ReplyReply Direct Link To This Post Posted: 26 Sep 2021 at 5:08am
Just to close this out.
On a recent flight, I tested removing the gap by only deleting BD111 from the arrival, and the FMS merged the two AROKA points as AviSteve described.

Cheers. E


Edited by eloigorri - 26 Sep 2021 at 5:09am
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