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suavi

False STAR Path Calculation - Turns at the opposite side

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Hello,I have seen this weird STAR path in my last two approaches (yesterday and today) to LOWI. As you will see in the attached pictures FMS calculates the leg transitions with turns at the opposite side in well known TULS3A STAR with RTT transition on LLZ 26 approach. If you leave the plane at LNAV mode it actually tries to follow it. I checked my log and noticed that I haven't flown that approach since Nov. 5th. Since then, I applied SP1b and Navigraph cycle 1113. Where do you think it comes from?Regards,Suavi Akar

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A bigger pics of the CDUs legs page would have helped maybe....sorry can´t see much with my eyes.A tip, If you know the route and approach, then maybe you could clean it up in CDU./ Leffe


Leif A Mikkelsen

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Hi Leffe,Thanks for the reply and suggestion to manage the situation. I uploaded higher resolution versions (1280x960 when you click) of the same shots. You may see the legs page on the captain's CDU at the first picture. As you will see it looks pretty normal. However the path drawn in ND has the interesting curly shape. There is something wrong in this STAR causing a mis-calculation of the interception. This has never happened at LOWI before and hasn't been appearing in other STARs or routes, I have flown so far. Therefore I consider either SP1b or AIRAC 1113 cause it. By the way I tried to delete and redefine the arrival procedure but it doesn't work. The way I followed is to switch to HDG mode until LOC capture. If you mean defining direct legs between TULSI - RTT and OEV21, I will give it a try next time, it may work as well.However, my purpose in starting this topic is to understand if other LOWI fans have experienced the same with other versions (mine was 600, how about 700, 800, 900) and bring the detail to the attention of PMDG team.Best regards,Suavi Akar

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I'm no expert but would suggest that if you edit the speed in the legs page to a lower value does this make a difference? this seems to help me when I experience similar problems on both SIDs and STARs.Hope this helps,Sam


Sam Iliya

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I think it does this for one of two reasons: 1) to get the altitude lower, or 2) to get the speed lower. Hope this helps.


Ron Musick, PP-ASEL-IA

AOPA # 00642403

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I seriously doubt any STARs are meant to have loops in them like that, nor would they be generated by high speed constraints. SIDs and STARs aren't "intelligent" and can't alter to add additional paths depending on the height and speed of the aircraft. It's up to the pilot to manage the speed and height correctly to match the defined path.I'd say the problem is in the navdata files. A turn in a SID or STAR can be coded in the navdata with a turn direction specified or none (which would mean the FMC choosing the least heading change). If an incorrect turn direction is specified then it can lead to loops like that in the approach path. Knowing which STAR was selected it would be easy enough to see whether a turn direction is given at the waypoints the loops appear at (the SIDSTARS files are just text files).Kevin Hall


ki9cAAb.jpg

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I think it does this for one of two reasons: 1) to get the altitude lower, or 2) to get the speed lower. Hope this helps.
I'm no expert but would suggest that if you edit the speed in the legs page to a lower value does this make a difference? this seems to help me when I experience similar problems on both SIDs and STARs.Hope this helps,Sam
Thank you guys. I have done what you have told, I have edited the altitude and speed restrictions of TULSI waypoint which is the initial fix of STAR. I thought this would not cause any problem as I have already been flying at lower altitude and slower speed than the planned values for it. I imagined that it would provide better slow down performance between TULSI and OEV21. But you are saying that it complicates everything and FMS somehow needs a longer path than physically exists, to descend and decelarete between these two fixes. I don't know how it could be possible in my particular case, normally I would expect to see a DES PATH UNACHIEVABLE message in CDU and VNAV disconnect instead of nice round curves in ND. I have been persuaded in another long discussion in another forum that FMS sometimes does strange things in 737. This could be another example among them. I will try it again and update.Best regards,Suavi Akar

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If the speeds for a turn are too high, you get a disconnect, not a circle. I'd bet the STAR is incorrectly coded.


Matt Cee

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Hello,I tried again, this time I added STAR procedure at the gate and see the same curly STAR path again. I corrected it by creating a direct link from RTT to OEV21 as Leffe proposed above.Regards,Suavi Akar

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I have also landed in Innsbruck this evening and I have the same problem. I did not have it with AIRAC 1112, only with 1113.When flying past the waypoints where the circles show up the aircraft does also fly those circles, so they aren't only mistakes in the visual, but really coded in the STAR.Installing the older AIRAC solves the problem, but as a online flyer I'm always needing the current one, so I'd like PMDG/Navigraph to make a fix for this one please.


Greetings from the 737 flightdeck!

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Emi, if you replace just lowi.txt in the SIDSTAR folder and let the rest be, you will get what is pretty much the current AIRAC, except LOWI will work.


--Peter Fabian 
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