Simviation Forum - Changing the FSX magnetic variation.

Feb 7^th, 2010 at 11:36pm

snippyfsxer Offline
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I have a 3 ring binder full of obsolete charts that all are around the 2006/2007 time frame. So, for example, KSEA, rw34R is pointed at 341 degrees magnetic in my chart (and in the FSX map)

No matter what date is set in the sim, FSX insists on giving a current magnetic variance...so in 2010, the current magnetic heading of KSEA 34R is actually 343 degrees, and that is how I'm pointed when I start the sim, lined up for takeoff. I guess FSX must be using the system time to calculate the current data. Obviously, using my obsolete charts, this can make for some less-than-precision IFR approaches. Also, since the FSX Map is apparently NOT compensating for changing magnetic variance, any flight plans created by the Planner also give slightly incorrect courses (I think). I can't believe I never factored this in before--I guess I thought I was just doing a sh*ty job compensating for crosswinds.

Is there any way to force the sim to use magnetic variance data from a different time? Is there a file I can modify or some method to force 2006 or 2007 magnetic data?

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Reply #1 - Feb 8^th, 2010 at 2:47pm

Fr. Bill Offline
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No. FSX is "fixed" into the world as it was in 2005. Nothing you can do will ever change that...

Bill
Gauge Programming - 3d Modeling Eaglesoft Development Group Intel Core 2 Quad Q6600-4GB DDR2 Crucial PC6400-800 GB SATA-ATI Radeon HD2400 Pro 256MB DX10 NOTE: Unless explicitly stated in the post, everything written by my hand is MY opinion. I do NOT speak for any company, real or imagined...

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Reply #2 - Feb 8^th, 2010 at 6:48pm

snippyfsxer Offline
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Fr. Bill wrote on Feb 8^th, 2010 at 2:47pm:

No. FSX is "fixed" into the world as it was in 2005. Nothing you can do will ever change that...

I believe you, but there has to be more to it than this. Start your sim on ANY airport, pointed down the runway and take note of your precise heading using shift-Z. Now go to your FSX map and see what it tells you about the alignment of the RW. You will see a discrepancy of 2 or 3 degrees. I just tried this with half a dozen airports and not a single one is correct. Strangely, the FSX map and my charts (2007) match each other, just not the actual compass in the sim itself.

Perhaps someone can tell me, using KSEA as an example, what was the alignment of rw34r in 2005? What about 2007 and 2010? Something is definitely incorrect here and it is not just my own installation.

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Reply #3 - Feb 8^th, 2010 at 10:47pm

Capt.Propwash Offline
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it may not be the runway itself that is messed up at all. It the the "start location" that was made in "AFCAD2.2.1" or "A.D.E." or whatever program was used to make the airport.

in FS9...

KSEA, 16L/34R, (16L is positioned at a center point of N47* 26.8391', W122* 18.4716' ... True Heading: 180.340 // Magnetic Variance: 19.4 // Magnetic Heading: 160.9) .... the "Start Location" for 16L is set at a heading of 180.300

rwy34R starting location is set at 0.3.

If you are flying NON-DEFAULT airport, whoever made the airport might either have their Variances wrong for that airport (which it does not seem being that they line up with your OLD Sectionals) but more that the Start Locations do not line up correctly to the runway.

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Reply #4 - Feb 8^th, 2010 at 11:20pm

snippyfsxer Offline
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I considered that the start locations might be screwed up as well, but that that isn't it.

Let me use another example, this time kpdx, portland, rw10L:

-The June 2007 ILS or LOC 10L chart gives a heading of 99 deg...
-The Jan 2010 chart still shows 99 deg...
-The fsx map shows 99...

Starting the airplane on the runway gives a heading of 102. It is definitely pointed straight down the runway.
Coming in for a landing using an FMS equipped plane the CDU confirms that the correct no-wind course to the runway is 102. Maybe if someone had a real chart from 2005, it would say 102..I don't know...Keep in mind, the fsx map says it is 99 degrees.

This has nothing to do with any of my addons. I am only using default airports. Also, I have an another installation of fsx on another computer. There are no addons, and it isn't even patched, just straight out of the box. The behavior is the same.

KSEA probably wasn't the best example to use previously, because in this case, the 2010 chart has changed, and runway 34R actually is pointed in the same direction as FSX (343), further confusing the issue.

This looks like a bug to me. Who knows how many airports this affects. Maybe all of them. Really surprised that nobody seems to have noticed this before...

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Reply #5 - Feb 9^th, 2010 at 2:45pm

Fr. Bill Offline
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snippyfsxer wrote on Feb 8^th, 2010 at 6:48pm:

Fr. Bill wrote on Feb 8^th, 2010 at 2:47pm:

No. FSX is "fixed" into the world as it was in 2005. Nothing you can do will ever change that...

I believe you, but there has to be more to it than this.

Well, if you are really into masochism, you are free to de-compile the magdec.bgl file in the ..\Scenery\BASE\Scenery folder and make the required corrections for all 45k+ airports to match your real world data...

...but, it would only benefit you, since copyright restrictions would prohibit distribution of the corrected magdec.bgl file...

Bill
Gauge Programming - 3d Modeling Eaglesoft Development Group Intel Core 2 Quad Q6600-4GB DDR2 Crucial PC6400-800 GB SATA-ATI Radeon HD2400 Pro 256MB DX10 NOTE: Unless explicitly stated in the post, everything written by my hand is MY opinion. I do NOT speak for any company, real or imagined...

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Reply #6 - Feb 9^th, 2010 at 5:37pm

Brett_Henderson Offline
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Funny.. as a pilot, and navigation enthusiast; I've never noticed this.

It's because I've never encountered a situation, where it would matter. The last time I cared about true vs magnetic north, was when teaching that cumbersome flight-planning routine to new pilots. You feel kinda guilty making them go through that.. because no pilot alive can hold a heading +/- a few degrees for any length of time.. but it's needed, because it drills home theories

When navigating by radio, you're only concered about relative headings/courses. A VOR radial will always lead you to a VOR, and intersecting radials, wll always intersect. Now of course, if you were using that intersection because it was a published fix.. we got problems, but again, not really, as real-world fixes are rarely hit exactly.

As for approaches.. Non-precision approaches (VOR/NDB), are just that. Not precise. A precision approach (ILS) is runway realtive, so if it's magnetic orientaion is off a bit, it doesn't matter.. you're tracing the runway "radial". And an ATC vectored (or your own navigation) ILS, will have you intercepting the ILS far enough out for any reasonable error (by you, or the FSX magnetic deviation).

In summary.. don't sweat it.. Cheesy

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Reply #7 - Feb 9^th, 2010 at 7:12pm

snippyfsxer Offline
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Brett_Henderson wrote on Feb 9^th, 2010 at 5:37pm:

As for approaches.. Non-precision approaches (VOR/NDB), are just that. Not precise. A precision approach (ILS) is runway realtive, so if it's magnetic orientaion is off a bit, it doesn't matter.. you're tracing the runway "radial". And an ATC vectored (or your own navigation) ILS, will have you intercepting the ILS far enough out for any reasonable error (by you, or the FSX magnetic deviation).

In summary.. don't sweat it.. Cheesy

This came up when flying a non-coupled precision approach in an fms/efis aircraft. Since I was doing everything by hand, I didn't select an approach in the fms (which actually would tell me the correct fsx magnetic heading), just used the chart. Since I was doing precision approaches in an a/c capable of such precision, this absolutely made a big difference. You dial in the rw heading into your course thingy and then put the efis into approach mode. The idea is to align the wind-corrected ground track diamond with the top of the HSI bar. Doing this, you will be flying in at a crab angle, corrected PRECISELY for the wind. If your approach data is wrong, and you are chasing the wrong course, inbound, then for all intent and purposes, the approach avionics on your MD-83 becomes no more usefull than the fixed VOR heads in a Cessna. Actually, it is even worse, because in the Cessna, at least you know that your adjustments for the crosswind are only approximate, and you expect your needle to wander and require constant corrections (don't you?). But in the more complex a/c you are left wondering why your instruments appear to be lying to you. "I'm flying the right ground track, I'm on the localizer momentarily, but I'm still drifting to the left, and I still can't see the runway... Oops, let the glideslope drift away and violated my minimums!"

Brett, If we are going for navigational accuracy in FSX, consider this: Your r/w chart tells you to fly outbound on the 159 radial of VOR Y for 60 miles to intersection X. However, unknown to you, in FSX, intersection X is actually located on the 161 radial. Even though you have done a grand job of keeping your needle centered, you will miss intersection X by 2 or 3 miles. So if you are flying old school, I'm not convinced that this is not a cause of signifigant navigational errors.
I'm not sweating it, or planning to mod 50,000 airports. I am considering putting FSX on the shelf for two or three years and waiting for the precession of earth's magnetic poles

No, not really. But I think this is something to keep in mind to keep getting the full enjoyment out of FSX. Thank god this is just a game, and I'm not a real pilot. There is no way I would have the brains to keep all these vectors and victors and angles and jangles straight in the real world.

« Last Edit: Feb 9^th, 2010 at 8:20pm by snippyfsxer »

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Reply #8 - Feb 9^th, 2010 at 8:26pm

Brett_Henderson Offline
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Ah.. I see your point, kinda. I don't fly big jets often. I have the CS757, and I'll use the FMS for the climb, cruise and descent.. I'll even fly a STAR, and then land visually, by hand... unless it IMC, then I'll use the ILS.. SO, I'd never encounter that problem.

As for old-school, radio navigation in my light GA aircraft... you're talking about a scenario that is rare, a best. My legs are rarely longer than 200nm, and I can't remember the last time I needed a radial intersection as more than a reference ..turning from one radial to another, at their intersection, as part of a well-planned course.., so a mile or two miss is harmless.

If the intersection (or DME point on a single radial) is a destination, a mile or two is more than close enough for VFR ..and even IFR, many times a mile or two is more accurate than the avionics themselves.. and an IFR flight will end with an approach (which I covered in the previous post).

That's why.. in lord knows how many years of simming, I've never even noticed this Cheesy

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Reply #9 - Feb 9^th, 2010 at 8:34pm

Brett_Henderson Offline
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Almost forgot.. I'm impressed that you're simming with realism and accuracy and an attention to detail at a level needed to discover this Cool

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