Just as with previous versions of X-Plane, a while after the initial version is released, most rw mag bearings become out of sync with reality.

At LPPT for instance, it now reads as 24º when it should be 25º and we have to set 24 in the CRS of our aircraft for ILS / RNAV approaches.

I know this has been debated before, and I know some at LR say this is residual and not important, but I honestly do not agree and think this should be taken with accuracy.

This is at a location with just 0.7ºW (2024-2029 model data), but I imagine it could be worst at, say, PAFA, PANC, etc...

Edited Thursday at 09:51 AM2 days by jcomm

Not sure exactly what you're referring to:

• Magnetic headings / tracks in procedures? Shouldn't these get taken care of through AIRAC updates though?

• The magnetic variation that X-Plane simulates when working out what heading a wet compass (or a heading indicator driven by a magnetometer) should display? According to this blog post, X-Plane contains a model for how magnetic variation will change over time that should be accurate until June 2028.

I think there's a third possibility for the issue you're seeing: On aircraft that use IRSs (such as most airliners), the IRSs directly provide a true heading; the magnetic heading displayed on the HSI/ND is actually calculated from the true heading using an on-board database of magnetic variation. (In other words, this is the exact opposite of what is done in small aircraft, where true heading is calculated from the measured magnetic heading.) If an addon simulates this accurately, the addon's own magnetic variation database may be out of date and may need to be updated.

Edit:

It's 23.96° at present for LPPT 02, so 24º is correct...

My bad :-/

sorry ....

Edited Thursday at 04:53 PM2 days by jcomm

Well, that value above is wrong after all - a query to the GPT :-)

Then I went with the Portuguese AIP and found:

MAG VAR (date) / Annual change

2º W (2020) / 0.17º decreasing

with RW02 true heading being 22.72º.

So indeed 24º is not right at all...

1 hour ago, jcomm said:

Well, that value above is wrong after all - a query to the GPT :-)

Then I went with the Portuguese AIP and found:

MAG VAR (date) / Annual change

2º W (2020) / 0.17º decreasing

with RW02 true heading being 22.72º.

So indeed 24º is not right at all...

Can you clarify where you're getting the 24º from? (This will help narrow down what the issue is.)

• Are you reading this from the heading indicator when lined up on the runway? (Which aircraft?)

• Or is this being displayed in your FMC?

• Or somewhere else?

To follow up, I've done a test in X-Plane to look at the underlying datarefs (which tells us what X-Plane itself is modeling and eliminates potential error sources from the aircraft).

I set myself up on runway 02 in the Cessna 172 (G1000 version). Here's what I found:

• sim/flightmodel/position/true_psi (true heading): 22.67
  This is pretty close to your "book" value of 22.72.

• sim/cockpit2/gauges/indicators/heading_AHARS_deg_mag_pilot: 23.67
  Correspondingly, the heading indicator displays "024".

• sim/flightmodel/position/magnetic_variation: 1.00.
  This is consistent with the magnetic heading above if we assume it uses the unusual convention that positive numbers mean "west". I think this is also consistent with the variation data from the AIP that you gave above: If the variation was 2 degrees W in 2020 and is decreasing by 0.17 degrees per year, it should now be 2 W - 6*0.17 = 0.98 W, which is very close to the value that X-Plane gives.

So I think this all checks out.

Looking at the Jeppesen chart for LPPT, it still shows the runway heading as 025 degrees and the variation as 2 degrees W. My assumption is that the charts have simply not been updated to account for the annual variation change since 2020.

In other words, I think you would see exactly the same discrepancy in the real world, and I don't think a difference of a single degree is going to cause any issues.

Edited Friday at 09:08 AM1 day by weaklink

What weaklink said. Its fine.

What is the Magnetic Declination at your location?

Magnetic Declination in Lisbon, Portugal

Magnetic declination in Lisbon, Portugal is -0.94. To instantly determine the magnetic declination at your location, go to magnetic-declination.com

We get these discussions every few months, and in 95% of all cases its users not understanding magnetic declination or the way that real world aviation sources treat and publish the varying declination, including slightly inaccurate ILS front-courses or VOR radial publication (notwithstanding great circle variation of magnetic bearing along a radial).

In pilot school we made up mnemonics like "West is best, East is least" to remember if you need to ADD or SUBTRACT a declination value from a true bearing if trying to figure out a magnetic bearing.

Portuguese AIP - RNP App (RNP Y RW 02) as of May 2026 reads for the approach & rw bearing: 025º (022.7º T) with VAR 02º W

Indeed since it's a West declination, 22.7 T + 2 ~ 24.7 M which rounds perfectly to 25º

But ! RNP Z Rw 02 as of 11 June 2026 already gives the bearing as 024º M ( 022.7º T) so, indeed Xp12 is actually being rather accurate !!!

I tested with the NCEP models, but @Jan, thx for that link above!

In the video bellow, uploaded last May, crew is using 025 for their CRS, and this was what made me think there was a problem ... My bad ...

Boeing 737 Cockpit | stunning views sunny Lisbon | ILS 02 | multi-view cockpit footage

but probably anytime soon we may start observing 024 being dialed instread.

In X-Plane 12 when using the Toliss 32N or the 737 NG I alredy set 024, and it works beautifully, but since the charts have been reading just until June 11th, 025, I thought it was a problem with Xp12... I was very WRONG :-)

Edited Friday at 02:18 PM1 day by jcomm

Funny little anecdote: The plane I fly (747-400) is getting old, and the IRS systems are not getting any updates anymore. The magnetic variation database is getting old and outdated, and therefore we are not allowed to conduct IFR autopilot coupled approaches to certain airports, anymore, for example BGSF.

The heading is actually off by one or two degrees against the chart at some airports, for example at EDDF I usually dial in 247 instead of 246 (the officially charted magnetic front course), it fits much better when flying the approach.

But the tolerance is much bigger, and ultimately when flying an approach without reference to true ground track, you don´t know if you are flying a few degrees off course due to some crosswind or due to a wrong declination value. Keep the needle in the middle and the wheels on the pavement, that is what matters.

Edited Friday at 08:45 PM1 day by Litjan

Interesting issue - you need an accurage magnetic variation value for non precision approaches - it is the 1 in 60 rule at play here so the error is magnified accordingly. Who is going to update not sure - seems the out of date AIRAC as well is something that LR just let go after XP11

5 hours ago, coastaldriver said:

Interesting issue - you need an accurage magnetic variation value for non precision approaches - it is the 1 in 60 rule at play here so the error is magnified accordingly. Who is going to update not sure - seems the out of date AIRAC as well is something that LR just let go after XP11

First, we established that everything is accurate in X-Plane. So no one needs to "update".
If I recall correctly, Philipp implemented a dynamic updating to keep magnetic declination accurate (whereas before X-Plane was accessing a static table). There may be local variations (ore deposits, etc.), but by and large the value should be accurate to the degree.

Second, a non precision approach is mostly governed by an external navigation aid, like a VOR or nowadays RNAV or GPS. Those are not susceptible to the "1/60" rule, you are either ON the defined approach radial/track or you are not. Magnetic variation will not play a large role here, especially since wind drift is likely going to have you fly a different magnetic heading than published, anyway.

The one exception would be an NDB approach, here the bearing you fly to/from the station is actually derived from the indication of magnetic heading that you read off in the aircraft. If I recall correctly, the accuracy required is +/- 5 degrees for those approaches, a one degree course error at typical distances (max 10NM) that you submit yourself to the guidance of the NDB on an IFR approach would amount to 1000 feet off-track, that sounds like much, but with the obstacle clearance and high minima associated with NDB approaches, this would not be a problem.

21 hours ago, Litjan said:

Funny little anecdote: The plane I fly (747-400) is getting old, and the IRS systems are not getting any updates anymore. The magnetic variation database is getting old and outdated, and therefore we are not allowed to conduct IFR autopilot coupled approaches to certain airports, anymore, for example BGSF.

Honeywell, who manufactures the IRS units used in many airliners and bizjets, released a Service Information Letter (SIL) quite some time ago to state that the internal magnetic variation tables stored in many of their models is now quite old and that pilots need to be aware of the possibility of heading discrepancies vs. published procedures.