Landing issue at VNNG using FMS Expansion pack

[AllanK 2]

Navigraph charts show that RW26 is at 261 degrees.

On approach via SIKTA, CD26 and FD26 the UNS-1 sets up a heading of 260 degrees. As a result the aircraft is not lined up with the runway and is to the left of the runway.

Navigraph charts are at AIRAC 2108 and the update has been applied to <P35> Flysimware Navdata.

P3D is V5.2 HF1.

Any idea where the issue lies?

[ark 1,288]

11 hours ago, AllanK said:

Navigraph charts show that RW26 is at 261 degrees.

On approach via SIKTA, CD26 and FD26 the UNS-1 sets up a heading of 260 degrees. As a result the aircraft is not lined up with the runway and is to the left of the runway.

Navigraph charts are at AIRAC 2108 and the update has been applied to <P35> Flysimware Navdata.

P3D is V5.2 HF1.

Any idea where the issue lies?

When I look at VNNG in LittlenavMap when using the P3Dv5 airport database, runway 26 is listed as "260 magnetic". If I load the P3Dv4 or FSX database, runway 26 is listed at 259 magnetic. Magnetic variation changes with time, and so it is not uncommon for the scenery in a sim to not be as up to date as the latest chart data.

What might help is updating the sim database using the tools at https://www.aero.sors.fr/.

Al

[AllanK 2]

Yes - I am aware of the difference between True and Magnetic.

When I load the above flight plan into FS-FlightControl it displays both True and magnetic bearings for each section of the course. For a lot of the course the bearings are the same except, importantly, for the final FD26 to RW26. It shows True of 261 and Magnetic 260.

Looking at the UNS-1 and comparing it to FS-FlightControl it always uses the Magnetic bearing.

As a baseline. I set up the same flight plan, from scratch, from VEBN to VNNG on a FSLabs A320. The approach was the same - VOR26Z - to fly through FD26 to RW26. This set up a bearing of 261 to the runway as shown on the Navigraph chart. I am certainly no expert but it would appear it is using True north and not affected by the underlying database in P3D.

So it seems to me that the odd-one out is the FMS.

As I have not noticed this anomaly on any other flight plan I am reluctant to apply the update you suggest.

Perhaps there could be a setting to get the FMS to use True or Magnetic North as required?

Any thoughts?

Allan

[ark 1,288]

35 minutes ago, AllanK said:

Yes - I am aware of the difference between True and Magnetic.

When I load the above flight plan into FS-FlightControl it displays both True and magnetic bearings for each section of the course. For a lot of the course the bearings are the same except, importantly, for the final FD26 to RW26. It shows True of 261 and Magnetic 260.

Looking at the UNS-1 and comparing it to FS-FlightControl it always uses the Magnetic bearing.

As a baseline. I set up the same flight plan, from scratch, from VEBN to VNNG on a FSLabs A320. The approach was the same - VOR26Z - to fly through FD26 to RW26. This set up a bearing of 261 to the runway as shown on the Navigraph chart. I am certainly no expert but it would appear it is using True north and not affected by the underlying database in P3D.

So it seems to me that the odd-one out is the FMS.

As I have not noticed this anomaly on any other flight plan I am reluctant to apply the update you suggest.

Perhaps there could be a setting to get the FMS to use True or Magnetic North as required?

Any thoughts?

Allan

My understanding is the courses displayed on approach charts, including Jeppesen charts, are magnetic courses unless specifically marked with a T for True (typically in the far North). So the magnetic course values in a particular area depend on the magnetic variation, which changes with time and has to be periodically updated. My only point here is the sim database ( where the runway is located) and the FMC database in the VNNG area may be using different values for the magnetic variation -- don't really know.

It is fortunate, as you mentioned above, that you have not noticed a general problem of this nature at other locations, because other than the database updates that I have suggested above, I don't know of anything that can be done at this point. Whether those updates would solve the 1 degree course difference problem at VNNG I can't say for sure.

To provide some perspective, I will also mention that a 1 degree course difference, or error, is well within other similar limits. To be qualified for IFR flight an aircraft's VOR receivers only have to be accurate to within + or - 4 degrees. And due to the expense involved, VOR stations are typically not corrected for changing magnetic variation until their magnetic course information (radials) are in error by a few degrees.

Comments from others welcome.

Al

 

 

[ark 1,288]

As another data point, I just tried the VOR/DME Z 26 approach into VNNG using the GTN750. The GTN750 flew a 260 track and brought the Lear in just slightly (about a runway width) to the left of the runway -- well within acceptable limits for landing if the runway was in sight at minimums.

I then repeated the approach this time using the VOR with a course of 261 dialed in. This brought me in lined up with the left edge of the runway -- so half a runway width to the left.

Al

Edited August 26, 2021 by ark