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Variations on ILS courses
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Daniel Estrada



Joined: 08 Jan 2015
Posts: 124
Location: Mexico City

PostPosted: Sun Dec 30, 2018 5:04 pm    Post subject: Variations on ILS courses Reply with quote

Hi,

I have a Jetmax cockpit, and I'm having problems with ILS courses almost pn every airport. Radio frequencie is OK, but the course differs by 1-4 degrees.

Example:

Dallas Forth Worth Chart say ILS freq for rwy 18R is 111.9 (IVYN), I set his freq on the radios and the correct ILS name is showed on the PFD... BUT the course I see is different from what the chart says...! the course in the chart is 176 and set it in MCP, but the PFD is 177. Also, the FMC shows 180 on the App Ref page... crazy, ha?!

I have updated navaids today and still having the same problem. No matter which airport I fly into. Also, I have my FMC data updated with navigraph services.

Any help...? thank you!
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Daniel Estrada
Mexico City

JetMax 737 SKTQ
ACE B737 Yoke
CH Pedals

PC1-P3D
Asus Maximus IX Code, CPU Intel i7, 7700K, Gskill,3200 16GB RAM, Nvidia 1080ti,

PC2-Sim-Avionics

180° Screen, 3 Optoma GT1080 Projectors


Last edited by Daniel Estrada on Thu Jan 03, 2019 9:05 pm; edited 2 times in total
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omera60



Joined: 18 Nov 2014
Posts: 145
Location: Istanbul

PostPosted: Mon Dec 31, 2018 2:15 am    Post subject: Reply with quote

Hi,

You need to update your airport database in Sim-A. From the LatestVersionInfo.txt in the Sim-A Documentation folder:

# New program - \Navigation_Data\Build_Position_Database.exe
Used to build a position database of runways and gates based on your custom scenery.

1) Copy \Navigation_Data\makerwys.exe to Main Flightsim folder and execute.
2) Copy the resulting r5.csv and g5.csv back to \Navigation_Data
3) Run Build_Position_Database.exe

I had the same issue as you but after doing this it is solved.
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Daniel Estrada



Joined: 08 Jan 2015
Posts: 124
Location: Mexico City

PostPosted: Mon Dec 31, 2018 1:18 pm    Post subject: Reply with quote

HI Omera60,

I just did what you sugest but it doesn't work. I'm still having the same problem. I dont know how to upload images here to show you some pics. Sad

what could be happening.

thanks in advance.
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Daniel Estrada
Mexico City

JetMax 737 SKTQ
ACE B737 Yoke
CH Pedals

PC1-P3D
Asus Maximus IX Code, CPU Intel i7, 7700K, Gskill,3200 16GB RAM, Nvidia 1080ti,

PC2-Sim-Avionics

180° Screen, 3 Optoma GT1080 Projectors
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MichaelYSSY



Joined: 06 Jan 2015
Posts: 632
Location: Sydney - Australia

PostPosted: Mon Dec 31, 2018 2:36 pm    Post subject: Reply with quote

Daniel

I know what you are talking about, I have the same discrepancy in my sim.

Really don't understand why it appeared all of a sudden.

I know all about magnetic variation, charts and all but this one puzzles me.


Michael
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MichaelYSSY



Joined: 06 Jan 2015
Posts: 632
Location: Sydney - Australia

PostPosted: Mon Dec 31, 2018 4:37 pm    Post subject: Reply with quote

Daniel

Preface - I use latest Navigraph Nav Data, I recently did Make Runways sync, I Use latest up to date Charts

I did a little research on ILS courses.
It's a complicated subject and a ever changing magnetic field.

Most governing bodies have a system in place to deal with this and seems that different countries apply different tolerances +or- in the magnetic variation before they apply changes to charts.
This is also complicates as there are different chart suppliers and I'm not sure how each handle these changes or if they just apply data from each of the worlds governing bodies.

In saying all that, I too get this variation in my sim
Lets take for instance Runway 16R at YSSY
Published magnetic course from AirservicesAustralia ERSA is 155 degrees
Published magnetic course from AirservicesAustralia ILS Approach Chart is 155 degrees
I checked ILS (IKS) in Navigraph Database that I have installed in my sim (latest version) and it has 155 as the course

In my sim when I look at PRF INI page the course is NOT 155 (I can't recall correctly but think it's 158, I will confirm next time I fly)

Now in looking at what I have said above my feeling is that it's most probably the way that the Avionics Suite is interpreting the True/Magnetic/Variation values but not sure why as all the data for the ILS courses is in Magnetic and in reality there is no need to apply Magnetic Variation as it has been applied in the NAV DATA supplied by NAVIGRAPH

Someone with more knowledge may be able to work it out but at this time I just use the course that is published in the Charts (I use up to date charts)
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Daniel Estrada



Joined: 08 Jan 2015
Posts: 124
Location: Mexico City

PostPosted: Tue Jan 01, 2019 10:25 pm    Post subject: Reply with quote

Michael,

Thank you very much for taking the time to responde and make a research. I also don't understand why is happening this. I remember everything was working OK, and suddenly this problem appeared. Don't know if other pilots have this same issue.

Also I think it has to do with SimA software... but really don't know. We need to wait and see what Mark H. can do for us, Smile

Thank you again.
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Daniel Estrada
Mexico City

JetMax 737 SKTQ
ACE B737 Yoke
CH Pedals

PC1-P3D
Asus Maximus IX Code, CPU Intel i7, 7700K, Gskill,3200 16GB RAM, Nvidia 1080ti,

PC2-Sim-Avionics

180° Screen, 3 Optoma GT1080 Projectors
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MarkHastings



Joined: 18 Jan 2006
Posts: 907
Location: UK

PostPosted: Wed Jan 02, 2019 3:12 pm    Post subject: Reply with quote

I've been looking into this over the last few days and here's what I've found.

This has always been a bit of a nightmare because :
    - The NavData we download from Navigraph is kept inline with real world data.
    - People use charts from various dates. (but lets assume they're the latest)
    - But,... the Navdata in P3D is not up to date.

There are multiple items that need addressing here so I'll take them one at a time and let you know the problem and what I've implemented to improve things.
1) The ILS Front Crs displayed on the CDU APPROACH page.
This was a simple correction.
I remember when I first implemented that page that there were a number of inconsistencies with the ILS data in the nd.mdb. I implemented what is technically known as a programming 'bodge' to get all of the Front Courses to display within a degree.
However looking at the latest data, this now appears to have been corrected and after trying numerous approaches the Front course in the navdata appears to be the correct magnetic course. Dancing

Now things start to get tricky...
As an example : the navdata says the ILS crs is 270 degrees, and your latest chart says the ILS crs is 270 degrees.
But the ILS Localizers are stored in the scenery BGL files with a magnetic heading... but that was using the magnetic heading whenever the scenery was compiled. ie 271 degrees.
Overtime the magnetic deviation changes and the nav data and charts are updated to reflect this, but the scenery files are static.

I've tried replacing the magdec.bgl in P3D with the latest found at
http://www.aero.sors.fr/, for me this has improved some things but the ILS front courses still do not fully align with real world.

If anyone has a solution to this please please share...

New Solution
So what I have done is to modify the Server to directly read the latest magdec.bgl file, and after using a bit of bilinear interpolation can determine the correct magnetic variance at a specific location.
I've check my output values using online MagVar calculators and they closely match.
So now the courses align.

Except.....
Even after applying the latest MagVar files some of the ILS Front Courses in P3D still do not match the real world course.
So with the chart and NavData saying 270 degrees and the P3D LOC still set at 271 degrees, we get a small left/right oscillation down the localizer as the A/P tries to track a 270 course down a 271 LOC.

So currently I've left it so that the real world data is correctly displayed in the FMC and correctly entered on the MCP CRS selectors, but in the background the A/P is actually tracking the P3D LOC course.
During testing I've only seen a 1 degree difference on some ILS, and will likely only be a max of a 2 degree difference.
But what you will see is a CRS of 270 displayed, and a CRS of 270 Set in the MCP... but with zero wind the Aircraft HDG will be 271 (or whatever the P3D scenery LOC CRS is)

I'm still running multiple tests on this and all being well will be included in 1.94.

Scenery design is not an area of FS that I know much about, so if anyone can help with a simple way of keeping P3D aligned with real world data... please let me know.
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kand



Joined: 03 Feb 2016
Posts: 183
Location: Buckinghamshire, UK

PostPosted: Wed Jan 02, 2019 6:27 pm    Post subject: Reply with quote

Not sure this will help this specific problem; however I cant say I have noticed this issue on my sim.

You can bring all of your P3D/FSX BGL navdata up to date by using this commercial service, you also need a navigraph subsription

www.fsaerodata.com

I have been using for some time and dont see any issues, only place i can recall problems with runway alignment on the ND was PHNL

Features:

Worldwide update of flight simulator navigation database including the following elements:

• Navaids: VORs, DME, NDB, TACAN, Enroute and Terminal Waypoints, (update identification IDs, frequency, coordinates, magnetic variation).

• Instrument Approaches, including SIDs and STARs procedures. Ability to fly curved radius-to-fix (RF) legs Approaches.

• Full database of VRP (Visual Reporting Points), with >5,000 waypoints mostly in Europe.

• Airways Routes, including High and Low altitude airways.

• Update of world's airspace: controlled (Class A-G, CTR, CTA, TMA, Radar, ATZ, Airways sectors,...) and restricted ( including among them MATZ sectors).

• Update of main enroute ARTCC / FIR Flight Information Regions, including boundaries, frequencies, names, locations.

• Full coverage of ARTCC / FIR real-world sectoring, including altitudes and center frequencies, for following countries: US, Canada and Western Europe.

• Update of Airport Comm Frequencies worldwide.

• Access to SIDs & STARs procedures on default GPS navigation unit (only Prepar3D).

• Update of Runway designators.

• Update of Airport Names and ICAO identifiers (more than 650 ICAO idents worldwide).

• ILS stations: update of frequency, name, Identifier, Magvar, correct heading acc published charts, DME and glideslope station. New stations added.

• Obsolete Navaids are disabled.

• Simulation of TACAN facilities (only Prepar3D).

• Air Traffic Control (ATC): Selection and aircraft vectoring of final approaches based on updated database.

• Capability to successfully execute real-world routes.

• Fully Compatible with new Prepar3D V4.

• Auto update of Magnetic Variation Table (MagVar) on flight simulator.
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MichaelYSSY



Joined: 06 Jan 2015
Posts: 632
Location: Sydney - Australia

PostPosted: Thu Jan 03, 2019 2:46 am    Post subject: Reply with quote

Hi Mark
Thank you for the input and explanation.

Once again things do not appear to be as easy as first thought.


Cheers
Michael
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Banananav



Joined: 08 Oct 2015
Posts: 69
Location: 5nm West of RAF Cranwell

PostPosted: Thu Jan 03, 2019 8:59 am    Post subject: Reply with quote

Hi Mark, et al

There are three related, but separate, issues here.

The key is Magnetic Variation which, as we all know changes with both place and time. In 1944 the Variation over London was 10 deg W, in 1975 it was 5 deg W, today it is Zero.

The first issue is the FMC approach page which is updated from Navigraph and Mark has sorted this one out - many thanks.

The second is the aircraft's compass presentation. This is generated in P3D by taking the true heading and applying variation from the magdec.bgl file in ...BASE\Scenery. This is exactly what happens in the real aircraft where true heading is generated by the INs and then degraded by Magnetic Variation from a look-up table which is not as accurate. This is easily sorted by using the aero.sors annual magdeg.bgl file update, 2019 is just out but it will degrade in accuracy over the next year. Incidentally, the aviation industry is looking at going to True, which the Maritime industry did years ago - but these things grind extremely slowly, needing international agreement.

The last is magnetic courses, not just ILS but also VOR and (for an inexplicable reason as they are interpreted at the aircraft and thus relative to its compass) NDBs. It also applies to magnetic courses specified along airways.

The problem here is that the mag variation at each station is contained in its own .bgl which can be years out of date. It is compounded by when we buy a new airfield add-on as its mag variation is up-to-date, so you can for example have Manchester and Pole Hill VORs using different variations !

The only current solution, identified by KAND above, is to use either the aerosors world wide (selectable by region) navaids update, or the selectable ILS one. I am about to give these a try.

LM have said that updating the world navigation database is becoming a priority but this a one-off solution and the changing variation will still be there. At least it would solve the occasional problem, such as at COMOX CFB, where the main runway is miss-placed.

This is all the product of us wanting greater and greater realism and accuracy, particularly if we are using real-world procedures on VATSIM or IVAO.

I feel a letter to PC Pilot coming on (they have published a couple of mine in the past) and it would have the advantage of highlighting the issue to LM and the add-on developers.

Cheers

Chris
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MarkHastings



Joined: 18 Jan 2006
Posts: 907
Location: UK

PostPosted: Thu Jan 03, 2019 11:24 am    Post subject: Reply with quote

ok - so I've just run the update from fsaerodata.
The ILS now all appear to have the correct front crs.

However the global magvar is still incorrect and at the moment I can't figure out how P3D is generating the value.

So currently :
KLAS rwy 26R
The Charts say the RWY and the LOC = 259
The FMC data says the LOC = 259
But sat on the RWY the HDG = 258 (258.4)

If I take the TRUE Rwy heading and add my calculated magvar from the latest magdec.bgl I get 259
But the P3D magvar is slightly different. ??? strange

However everything is MUCH closer now...

Still working on it... Brick wall
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Banananav



Joined: 08 Oct 2015
Posts: 69
Location: 5nm West of RAF Cranwell

PostPosted: Thu Jan 03, 2019 12:21 pm    Post subject: Reply with quote

Looking at the differences in longitude between the 08L and 26R thresholds the difference in northings = 15 ft. This gives a true bearing of 26R of 269.994 deg.

The published mag var for KLAS today is 11 deg East. But this means that it lies between 10.5 and 11.5 deg East. Lines of mag var on navigational charts (isogonals) are drawn on the .5 degrees and one changed the variation by 1 deg as you crossed them.

270 - 11.5 = 258.5 so this could all be within the rounding error.

Chris
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Banananav



Joined: 08 Oct 2015
Posts: 69
Location: 5nm West of RAF Cranwell

PostPosted: Thu Jan 03, 2019 12:46 pm    Post subject: Reply with quote

Some further thoughts:
Did FSAERODATA update the magdec.bgl file ?
Did it update the KLAS local variation if you have any payware, even just Global Vector and not an airport ?
You could try the 2019 magdec.bgl from aero.sors.fr and see if you get a different answer.
Chris
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Banananav



Joined: 08 Oct 2015
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Location: 5nm West of RAF Cranwell

PostPosted: Thu Jan 03, 2019 3:03 pm    Post subject: Reply with quote

And a few more:

I have just updated P3D v4.4 on my general purpose Pc (not the one I use for my Jetmax 737) with aero.sors 2019 magdec.bgl and their European Nav aid update and can report the following:

As indicated aero.sor does not update add-on airfields (nor does Fsaerodata).

I checked an ORBX EU ENG airfield, EGNX, and found that the mag var on the ILS was 3W, it is currently 1W.

I assume, and will check, if that is also so for ORBX, UK2000 and Aerosoft stand-alone airfields.

There is also a possible issue with ORBX Global Vector which contains some airfield .bgls. These are the ones that can cause elevation conflicts with their stand-alone airfields eg Kiruna.

I have yet to look at airfield VORs such as at Manchester.

But the picture is emerging that whilst it is easy to update the “stock” navaids mag var it is much more difficult if, as I suspect most of us do, one has a lot of add-on airfields and ORBX regions.

What a “can of worms” you have opened, Daniel !

Chris
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MichaelYSSY



Joined: 06 Jan 2015
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PostPosted: Thu Jan 03, 2019 3:41 pm    Post subject: Reply with quote

So

Not a simple fix.
Really a lot more complicated

Confused

Michael
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