The magnetic variation for ZGNN is incorrect. It is stated as 2E in the flight configuration menu but it is 2W. This may be the reason why the ILS localiser does not align with the runway. ILS 05 causes the aircraft to land well East of the runway. It does fly over the VOR WUY which appears to be correctly located but not the LLZ.
OK. I downloaded the ZGNN scenery file above. The ILS worked just great until the around 400'AGL and then the aircraft did a sharp turn to the right. After checking again twice the same behaviour, I went back to the navdata files where I had changed some of the co-ordinates on the default ZGNN database in X Plane and re-input the original data. All works well now. I suspect the lat/long for the original file is based on WGS84 co-ordinates which China was not using in the earlier days. The variation in the default X Plane database does need to be changed to 2W though.
There is no way for user to modify the magnetic variation for any given location - neither in scenery files nor by hacking any simulator files.
The magnetic variation data used in the sim was updated the last time to the 2015 epoch, in this particular location the annual change rate is quite low - only 4 arc minutes per year. And the magnetic variation model in the sim has of course, finite and not stated accuracy ...
I do not know where the OP thinks he see's the magnetic variation being 2E in the sim. If I place an aircraft there - turning the aircraft to a true north heading the C-172 compass indicates slighly west of north.
And if the simulators navdata databases are changed by users as hkgdragon mentions - all bet's are off as well.
In the recommended submission for this airport, the ILS alignment is perfect for this runway in both directions (attached). Perhaps this is an autopilot issue or flight plan issue? Is the autopilot discontinuing the approach at 400 feet - perhaps a missed approach / auto-land thing?
Thank-you for all your comments. The correct term is magnetic variation and the current variation at Nanning (Wuxu) China is 2W. I have screenshot the page from X Plane where it states 2E. I have also attached some of the latest NavBlue Chart showing the current variation of 2W. I do not know how the maths that is programmed for X-Plane will be affected by the variation effectively being 4 degrees off...?
The ILS for 05 is just off the centreline to the left for landing and the ILS 23 is completely unflyable. The LOC will not capture at all. Perhaps there is a conflict between the download ZGNN file downloaded here from restavr and the default Global scenery from X-Plane 11. Have you actually flown the ILS 05/23 for ZGNN on your X-Plane...?
ILS 05 is acceptable but I've discovered the problem with the ILS 23 is it wants to fly the 05 LLZ. So it I head in the opposite direction of ILS 23 i.e. track outbound 048, the LOC will intercept for ILS 23!! If I try to fly the ILS 23, the LOC will always try to make me turn 180 degrees until I'm tracking outbound on the LLZ...
Sounds like someone has downwind ILS turned off here .. and then flying backcourse approaches all the time.
So check the flows as well - as these determine which ILS would be active.
The magnetic variation for ZGNN is incorrect. It is stated as 2E in the flight configuration menu but it is 2W. This may be the reason why the ILS localiser does not align with the runway. ILS 05 causes the aircraft to land well East of the runway. It does fly over the VOR WUY which appears to be correctly located but not the LLZ.
hkgdragon March 13, 2019 6:26 AM
OK. I downloaded the ZGNN scenery file above. The ILS worked just great until the around 400'AGL and then the aircraft did a sharp turn to the right. After checking again twice the same behaviour, I went back to the navdata files where I had changed some of the co-ordinates on the default ZGNN database in X Plane and re-input the original data. All works well now. I suspect the lat/long for the original file is based on WGS84 co-ordinates which China was not using in the earlier days. The variation in the default X Plane database does need to be changed to 2W though.
restavr March 13, 2019 2:42 PM
I have not found where to change the magnetic declination for ZGN to the correct one. Please specify the location.
Michael Minnhaar March 13, 2019 5:36 PM
There is no way for user to modify the magnetic variation for any given location - neither in scenery files nor by hacking any simulator files.
The magnetic variation data used in the sim was updated the last time to the 2015 epoch, in this particular location the annual change rate is quite low - only 4 arc minutes per year. And the magnetic variation model in the sim has of course, finite and not stated accuracy ...
I do not know where the OP thinks he see's the magnetic variation being 2E in the sim. If I place an aircraft there - turning the aircraft to a true north heading the C-172 compass indicates slighly west of north.
And if the simulators navdata databases are changed by users as hkgdragon mentions - all bet's are off as well.
Julian Lockwood March 16, 2019 3:02 AM
In the recommended submission for this airport, the ILS alignment is perfect for this runway in both directions (attached). Perhaps this is an autopilot issue or flight plan issue? Is the autopilot discontinuing the approach at 400 feet - perhaps a missed approach / auto-land thing?
hkgdragon March 16, 2019 3:30 AM
Thank-you for all your comments. The correct term is magnetic variation and the current variation at Nanning (Wuxu) China is 2W. I have screenshot the page from X Plane where it states 2E. I have also attached some of the latest NavBlue Chart showing the current variation of 2W. I do not know how the maths that is programmed for X-Plane will be affected by the variation effectively being 4 degrees off...?
hkgdragon March 16, 2019 3:39 AM
The ILS for 05 is just off the centreline to the left for landing and the ILS 23 is completely unflyable. The LOC will not capture at all. Perhaps there is a conflict between the download ZGNN file downloaded here from restavr and the default Global scenery from X-Plane 11. Have you actually flown the ILS 05/23 for ZGNN on your X-Plane...?
hkgdragon March 16, 2019 4:11 AM
ILS 05 is acceptable but I've discovered the problem with the ILS 23 is it wants to fly the 05 LLZ. So it I head in the opposite direction of ILS 23 i.e. track outbound 048, the LOC will intercept for ILS 23!! If I try to fly the ILS 23, the LOC will always try to make me turn 180 degrees until I'm tracking outbound on the LLZ...
Michael Minnhaar March 16, 2019 10:40 PM
Sounds like someone has downwind ILS turned off here .. and then flying backcourse approaches all the time.
So check the flows as well - as these determine which ILS would be active.
Robin Peel May 25, 2019 5:55 PM
Thanks! The update to ZGNN ILS 05 and the new ILS 23 will be included in the next release of X-Plane that includes updated ILS data.
This was not an issue with magnetic variation, rather just old data and a misplaced localiser aerial. The ILS 23 was missing, so I have added it.