MadBilo

PMDG LNAV issue

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Hello, I don't know if this has been dealt with previously but I did do a lot of searching but couldn't find any answers to this problem. 
 

 

So, what the problem is that I am trying to do a procedural approach as shown below this text is the chart I am trying to use while doing it, so I have seen a video on YouTube of the real aircraft (737-800) doing this same approach to RWY 05R. I thought let me try do it as well, so I done everything per usual to what I normally and everything was fine I was descending on the VNAV path and LNAV was perfect but then when I reached around D11 VSJ on the FMC and you can see on the chart there is a turn heading 047, so I saw this in the video and they left it in LNAV so I decided to leave it too but what I didn't understand that when my plane was turning it managed to turn so much that it levelled off for  bit then it carried on again. However, when I was looking at the video of the real aircraft, somehow it managed to bank perfectly on the magenta line. 

b0be826117784ea4a4b3151a975aac56.pngf7d51541943640bca96f2e400d81dde3.png

And now this is what my plane does in the sim, I disabled all the weather set it to clear.f50ea3b177aa4fb4bd84ab9b2c1cf6c9.png3af8f3809bcf487ab725a2e9d80081ab.png

As much as I love this aircraft these little things make me sad, anyways its nothing big but a solution will be amazing for me :)
 

I also realised something here in the real life picture you can see the VOR DME clearly on the ND but on mine its blocked, hmmm anyways if you guys can help me with the magenta line and LNAV that will be superb.
b06cb420757c43ce99ce8adc04e74f9b.png

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Necmi Osman

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The solution is not easy.  The flight dynamics of a turn rely somewhat on the simulator's internal flight dynamics engine and in this respect it does a very poor job.  One thing to try is your speed, you are in the terminal environment performing a terminal procedure and you should be at 180 KIAS or less (notice the guy in the video is trying to get there).  That might not fix it.  A big help would be a set of navdata with a set of pseudowaypoints to establish the arc, in real world the navdata has defined the radius to fix arc but the old navdata we use is limited.  So a complete fix would be flight dynamics totally divorced from the underlying platform and ARINC421 formatted navdata.

I prefer to handfly these type of procedures, which is what that teardrop entry is designed to support.  Newer instrument procedures designed for FMC capable aircraft will dispense with teardrops and procedure turns.

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23 minutes ago, downscc said:

The solution is not easy.  The flight dynamics of a turn rely somewhat on the simulator's internal flight dynamics engine and in this respect it does a very poor job.  One thing to try is your speed, you are in the terminal environment performing a terminal procedure and you should be at 180 KIAS or less (notice the guy in the video is trying to get there).  That might not fix it.  A big help would be a set of navdata with a set of pseudowaypoints to establish the arc, in real world the navdata has defined the radius to fix arc but the old navdata we use is limited.  So a complete fix would be flight dynamics totally divorced from the underlying platform and ARINC421 formatted navdata.

I prefer to handfly these type of procedures, which is what that teardrop entry is designed to support.  Newer instrument procedures designed for FMC capable aircraft will dispense with teardrops and procedure turns.

Thank you very much for the reply, I understand now, thank you. Just one question, do you think in time PMDG will be able to fix this or will it permanently be like this? Im thinking 64 bit might open more windows but of course you have more knowledge about this then I do, once again thank you for the reply.

Necmi Osman

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I think PMDG is going to modern navdata soon but it will take time to incorporate into each product because it involves major changes to FMC code.  As for the turn dynamics..... I don't know.  I know at least one designer that wants to but the want list is so long..., I don't know.  This has nothing to do with 32b/64b.

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1 minute ago, downscc said:

I think PMDG is going to modern navdata soon but it will take time to incorporate into each product because it involves major changes to FMC code.  As for the turn dynamics..... I don't know.  I know at least one designer that wants to but the want list is so long..., I don't know.  This has nothing to do with 32b/64b.

Anyways, Dan. Thank you very much for replying to me means a lot, take care enjoy the rest of your day.

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It's in my opinion, the most sad and unrealistic behavior of the NGX.

Even when creating pseudo-waypoints like Dan said, the plane sometimes just doesn't turns enough to follow the magenta, the interception and maintenance of the magenta (lateral track) is VERY poor compared to the real aircraft, which basically nails 0.00 XTRK.

In NGX you will have to HDG SEL the approach to make finer adjustments, and antecipate things. 

We all hope they develop a better navdatabase system (with RNP) and fix the tracking and turns of the acft.

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5 hours ago, zazaboeing said:

It's in my opinion, the most sad and unrealistic behavior of the NGX.

Even when creating pseudo-waypoints like Dan said, the plane sometimes just doesn't turns enough to follow the magenta, the interception and maintenance of the magenta (lateral track) is VERY poor compared to the real aircraft, which basically nails 0.00 XTRK.

In NGX you will have to HDG SEL the approach to make finer adjustments, and antecipate things. 

We all hope they develop a better navdatabase system (with RNP) and fix the tracking and turns of the acft.

I agree with you 100%. I think this is the most sad part about the NGX, everything else is amazing but for me personally it takes the immersion straight away. I even sometimes have problems with ALT HOLD, it goes 100 feet below or top and then tries to recover but to be honest if they fix the LNAV issue, I will be the happiest guy in the world. 

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I don't believe this is an lnav / vnav approach ......but need to see the full chart.

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2 minutes ago, vadriver said:

I don't believe this is an lnav / vnav approach ......but need to see the full chart.

012de3c139d6495293c7132656d6d9da.png

Just for the heads up I was trying to do what the real pilots done in this video to see how my LNAV reacted comparing it to them, my intention was not to capture the ILS nor land the plane just to see how it copes with LNAV comparing it to the real thing.

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8 hours ago, zazaboeing said:

It's in my opinion, the most sad and unrealistic behavior of the NGX.

Even when creating pseudo-waypoints like Dan said, the plane sometimes just doesn't turns enough to follow the magenta, the interception and maintenance of the magenta (lateral track) is VERY poor compared to the real aircraft, which basically nails 0.00 XTRK.

In NGX you will have to HDG SEL the approach to make finer adjustments, and antecipate things. 

We all hope they develop a better navdatabase system (with RNP) and fix the tracking and turns of the acft.

 

Exactly right, the real aircraft has no problem and ANP is usually 0nm and flying on the magenta line. I've noticed the PMDG does struggle flying ARC's and flying the magenta line whilst holding in comparison to the real aircraft, still an outstanding product none the less.

 

1 hour ago, MadBilo said:

012de3c139d6495293c7132656d6d9da.png

Just for the heads up I was trying to do what the real pilots done in this video to see how my LNAV reacted comparing it to them, my intention was not to capture the ILS nor land the plane just to see how it copes with LNAV comparing it to the real thing.

 

Flown this Approach IRL several times, from the North VLC Radar would usually clear us direct to DITRE then VSJ for ILS Y 05R.

We'd use VNAV/LNAV for the entire approach and turning final, we'd arm APP when within 90 degrees of the intercept to capture the LOC/GP and LNAV does a cracking job, like in that photo, of tracking the magenta line. 

If the FMC thinks it won't be able to stay on the Magenta line you'll get "Bypass" appear on the FMC Legs page so you'd enter a speed restriction to ensure the aircraft can track the magenta line accurately. In this example for Murcia VSJ - 220B for the outbound leg and at D11 VSJ (VSJ-11) we'd enter 180B - this would be flown at Flap 5 to ensure track keeping. 

If you get a Bypass the aircraft, in LNAV, will bank up to 30 degrees to get back onto the magenta line but this is usually catered for by an existing speed restriction on the departure/approach or missed approach.

 

Hopefully looked into with a future update! 

 

 

 

 

 

 

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31 minutes ago, flightdeck2sim said:

 

Exactly right, the real aircraft has no problem and ANP is usually 0nm and flying on the magenta line. I've noticed the PMDG does struggle flying ARC's and flying the magenta line whilst holding in comparison to the real aircraft, still an outstanding product none the less.

 

 

Flown this Approach IRL several times, from the North VLC Radar would usually clear us direct to DITRE then VSJ for ILS Y 05R.

We'd use VNAV/LNAV for the entire approach and turning final, we'd arm APP when within 90 degrees of the intercept to capture the LOC/GP and LNAV does a cracking job, like in that photo, of tracking the magenta line. 

If the FMC thinks it won't be able to stay on the Magenta line you'll get "Bypass" appear on the FMC Legs page so you'd enter a speed restriction to ensure the aircraft can track the magenta line accurately. In this example for Murcia VSJ - 220B for the outbound leg and at D11 VSJ (VSJ-11) we'd enter 180B - this would be flown at Flap 5 to ensure track keeping. 

If you get a Bypass the aircraft, in LNAV, will bank up to 30 degrees to get back onto the magenta line but this is usually catered for by an existing speed restriction on the departure/approach or missed approach.

 

Hopefully looked into with a future update! 

 

 

 

 

 

 

Thank you for a wonderful reply sir, I mean I really this aircraft, I saw the video of your operator landing at this airport and that's why I wanted to try and see how the PMDG will do and the results are clear, Hopefully one day they will be able update or something.

nevertheless, keep your videos coming :) 

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