Incorrect airport magdev using MakeRwys

[pdubost]

Hi Pete

 

I am new on this forum, and want to thak you for your outstanding software products.

 

I have a question on MakeRwys, trying to fix the "wrong rwys" issue in RAAS in the PMDG777;

 

I am getting incorrect magnetic deviation, and therefore incorrect rwy magnetic heading and rwy names even after I ran your MakeRwys program. I have the latest Magdev.bgl file from easyNavs installed in Scenery/Base/scenery.

 

My question is where do you get the magnetic deviation information ?

 

Thanks

Pierre

[Pete Dowson]

My question is where do you get the magnetic deviation information ?

 

Thanks

Pierre

 

You'll need to be specific as to which data entry in which of the many files. However, where mag var is included it is direct from the airport data in the scenery BGLs, as those are the only files being processed. If you are using out of date scenery but up to date MAGDEVs then there will of course be discrepancies.  Runway names are exactly those in the BGLs -- changing the MagVar does not automatically change runway names, you have to edit the airports to do that.

 

Of course programs reading the magnetic runway heading and the associated magvar can therby compute the True heading and re-adjust for a different prevailing MagVar from yor MAGDEC file. This won't change runways numbers though.

 

Pete

[pdubost]

Hello Pete

 

Thanks for your quick response, but I am still confused.

 

My understanding was that the airport BGLs contained rwy TRUE headings. For example, if I look at TFFR, it reads 100,90 ° rounded to 101. Then the magnetic variation is added (I assumed from the Magdev.BGL file) to compute the runway Magnetic heading.

The airport.CSV file from MakeRwys for TFFR shows a magdev of 14° (2004 data?) leading to a rwy heading of 115° for rwy 11. Did you get this 14° also from the bgl file ?

 

The real magdev in 2013 in TFFR is 15° leading to a rwy heading of 116° for rwy 12.

 

thanks for your help !

Pierre

Edited October 10, 2013 by pdubost

[Pete Dowson]

My understanding was that the airport BGLs contained rwy TRUE headings. For example, if I look at TFFR, it reads 100,90 ° rounded to 101. Then the magnetic variation is added (I assumed from the Magdev.BGL file) to compute the runway Magnetic heading.

The airport.CSV file from MakeRwys for TFFR shows a magdev of 14° (2004 data?) leading to a rwy heading of 115° for rwy 11. Did you get this 14° also from the bgl file ?

 

Yes. ALL THE DATA IS FROM THE AIRPORT DATA BGLs! As I did say already.

 

The files produced contain the data the people requesting those files wanted. They wanted the Magnetic Heading, so the program computes it

 

The real magdev in 2013 in TFFR is 15° leading to a rwy heading of 116° for rwy 12.

 

By "real" you mean "current" presumably. You'll need to update the scenery if you want everything to match.  I tend to only fly commercial or recently made freeware airports and they are more up to date than the originals, of course. I also only fly FSX so the oldest ones would be 2006 not 2004. With original FS9 airports you will of course notice these differences. Either you have to update airports, or stick with old AIRAC data.

 

You can get quite a lot of fs data updated by using Herve Sors files, which he keeps level with Airac releases. Have you tried those?  http://www.aero.sors.fr/navaids2.html. Mind you, I don't think even he does the runways and ILSs. Runway numbering is definitely an airport editing job.

 

Pete

[pdubost]

Thanks Pete for the explanation !

 

I did not realize that there is a magdev field (optional but mostly always filled)  in the airport bgl file. I guess that the base magdev.bgl file is only used by default if that airport.bgl field is not filled.

 

I used the " Magvar corrector" program from aero.sors and it does fix correctly the runway magnetic heading with the current magnetic deviation. The name of the runway remains unfixed (e.g. in TFFR heading 116 but rwy 11 !). I will use an Excel formula to fix it automatically in runway.csv by computing the runway name from the current magneting heading, and that should close the RAAS issue.

 

thank you again for the very helpful advice !

 

regards

Pierre

[Pete Dowson]

I did not realize that there is a magdev field (optional but mostly always filled)  in the airport bgl file. I guess that the base magdev.bgl file is only used by default if that airport.bgl field is not filled.

 

Well, if the MagVar is wrong in the Airport data, the MakeRunways files will be wrong too. There's really no such thing as a field "not being filled" because the records have a fixed structure and there's no way of signalling that the fields present do not hold valid data.

 

The name of the runway remains unfixed (e.g. in TFFR heading 116 but rwy 11 !). I will use an Excel formula to fix it automatically in runway.csv by computing the runway name from the current magneting heading, and that should close the RAAS issue.

 

 

Yes, but it won't change the label on the tarmac! ;-)

 

Regards

Pete

[hsors]

 

 

Well, if the MagVar is wrong in the Airport data, the MakeRunways files will be wrong too

 

That's often the case now, even for FSX. Note that the airport magnetic variation as coded in the BGLs is probably only used internally for calculating mag data for AI trafic..I'm not aware of any other effect changing it.

Magnetic runway heading is calculated by FS from true heading and magnetic variation at airport position from the magdec.bgl file

However, even taking this approach doesn't ensure it will fit charts as far as in real life, airport aeronautical data make use of a "local" magnetic variation value that may differ a bit from any "calculated" one at a given time (e.g. some airports in US and Asia still use 2005 values, most European airports use 2010, UK now use 2013, etc)

Consequently there is no simple solution for correcting FS data as a whole

[Pete Dowson]

Note that the airport magnetic variation as coded in the BGLs is probably only used internally for calculating mag data for AI trafic..I'm not aware of any other effect changing it.

Magnetic runway heading is calculated by FS from true heading and magnetic variation at airport position from the magdec.bgl file

 

Really? How odd. I've never had many problems with the airport files -- the Mag Var in those should be fine. And in any case some of my experiences seem to differ from what you say. The ILS for the freeware Prague airport for FSX was about 30 degrees out. I checked the airport BGL and found the author had made an error in one of the ILS definitions with a decimal point -- a magvar of 30 instead of 3 (if I remember the numbers correctly). This did affect the ILS alignment. Maybe those are corrected by Herve Sors updates, but at the time Ihadn't discovered those, so edited the BGL instead.

 

So not all Magvar uses are derived from the Magdec BGL. I didn't know the Airport one was ignored for most purposes. Seems a damned waste as that seems to be the perfect place for the airport computations needed, and of course is why MakeRunways uses it.

 

Consequently there is no simple solution for correcting FS data as a whole

 

Except keeping airport scenery up to date if you intend to update the AIRAC data you use.

 

For many years whilst I was flying FS98 I used a complete leather bound World Wide paper set of Jeppesen charts, my pride and joy at the time and my biggest expense other than the PC I ran FS on. In order to enjoy those to the full I never updated anything past the date of the simulator data. Everything matched all of the time. A frozen time warp, if you like. It almost broke my heart recently to give those cherished manuals up, but they had long lost their real usefulness (I gave them to a charitable cause).

 

Those who really need up to date data all the time will really need to either stick to those airports which are relatively frequenty updated, or learn to use one of the airport editors to update their data. These days I do a bit of both.

 

Regards

Pete

[hsors]

 

 

The ILS for the freeware Prague airport for FSX was about 30 degrees out. I checked the airport BGL and found the author had made an error in one of the ILS definitions with a decimal point -- a magvar of 30 instead of 3 (if I remember the numbers correctly). This did affect the ILS alignment. Maybe those are corrected by Herve Sors updates, but at the time Ihadn't discovered those, so edited the BGL instead.

 

Agree Pete but it is a separate field included in each ILS definition (<Ils magvar). This value is indeed of importance for properly displaying ILS magnetic tracks on GPS and map views

It is not the airport magnetic variation that is included in the parent <Airport definition. That's what I ment

 

 

 

Those who really need up to date data all the time will really need to either stick to those airports which are relatively frequenty updated, or learn to use one of the airport editors to update their data

 

Yes. What I wanted to say is that keeping most airport sceneries up to date is probably unachievable especially considering the monthly changes worldwide in ILSs, runway identifiers, taxiway signs, instrument approaches, etc..

What I've done in my updates is correct all navaids (including their magnetic declination because they also have a specific one that is important for properly aligning on a specific radial) ) even if it raises some problems in the flight plan generator (most don't use anymore btw). I also corrected European ILSs and runway information for FS9 on a regular basis but didn't do that worldwide neither I did it for FSX (except France) since it is a never ending painstaking task that requires decompilation/recompilation of stock BGL files (with also possible side effects). Agree that selective airport exclusion/edition with appropriate software is a better way for most.

 

Regards

 

Hervé       

[mgh]

To the best of my recollection, FSX gets all its  values from magdec.bgl except for VORs and NDBs, and it ignores values in airport bgls.