ILS Vertical Bar Error

I have tested on 3 Caucasus airfields; Kutaisi, Kobuleti and Batumi. In every case I landed in the runway direction indicated by the ATC. There was no wind.

In every case the vertical bar directed me to a path to the left, off the runway axis. Had I followed this indication I would have crashed way outside the airport.

The horizontal bar directed me to an apparently correct glide path.

I am convinced that this is a bug.

I get normal steering on CDI for those runways with no wind. By "vertical bar" do you mean the CDI or the yellow bank command bar?

Because they yellow bank command bar doesn't work like the real airplane.

I am talking about the vertical localizer bar which is yellow. According to the A-10C flight manual "The vertical localizer bar indicates if you are left or right of runway alignment. If the bar is right of ADI center, fly to the right to center it. For a proper glide slope approach, you want the two bars centered and forming a perfect cross on the ADI (aka “center the bars”)."

If I'm flying straight abeam the runway and there is no crosswind, that bar should be centered. Instead it is left of center. And if I steer left to center it I will not land on the runway. That's a bug.

The manual is inexact. That is the bank command bar. It tells you to bank left and right more or less. What bank it commands is more complicated than telling you to bank right if you are left of course. For example if you are in a steep right bank and left of course it will command left bank (or less right bank) because that right bank is excessive even though you should be going right.

The real airplane commands bank based on position, rate, and progress along intercept (compensating sensitivity as you approach the runway). What it wants is centered and no change rate. The desired change rate is a function of lateral position. The more out of position the more change rate it wants, less less. The commanded bank is a function of the rate compared to the desired rate. If your rate is more than desired it commands a bank change away (or less toward).

All of this happens just by measuring the ILS localizer signal mixture and rate of change.

What DCS does wrong is base the bank command off the CRS knob setting. If you get on course and wiggle the CRS knob around you'll see the bank command bar go bananas. It should not do that. All that you should see is the HSI card spin around but the yellow bar should be unaffected.

So in DCS with the yellow bank command bar you have to recognize that it don't work like it should. You can get useful information out of it but only if you carefully set the CRS knob to the inbound course. Alternatively you can stow the command bars and fly the primary position readout on the CDI deflection and the diamond glide slope thingy on the left of the ADI.

Yup. You don't want to use the command bars on the ADI to get on the ILS. Use the CDI needle on the HSI to get you onto the localizer. Make sure your course needle is set for the runway heading and keep the CDI needle centered, with the course needle and desired heading at the 12 o'clock position on the HSI. When you intercept the outer lobe of the glideslope, your VDI will appear on the ADI. When you get near the center of your glideslope, you'll see that lateral command bar snap to the center, and it will track with your movement inside the ILS cone. It is a little squirrely compared to the real thing when you're outside the capture parameters, but once you hit the capture point, it locks on and tracks, just like its supposed to.

...So in DCS with the yellow bank command bar you have to recognize that it don't work like it should.

The short of the long is: It doesn not work correctly. So it's a bug.

As long as that's the case I will not do ILS landings.

Hi LeCuvier, I tried this again, paying more attention to my needles than the visual, and you're right, this thing is borked. I didn't even have the command bars in view this time, so I'm not sure if what I saw is the cause of what you're seeing, but the actual runway heading of runway 13 at Batumi appears to be 120 degrees (not 130 like it should be). Cross checked with the Whiskey compass. Velocity vector centered, so no cross-wind. So, if you have your HSI course needle set for 130 like you should, you're going to end up to the right of the runway by a long way, so maybe that's why the lateral deviation command bar is to the left when you're flying the heading the runway is supposed to be. Yup. This is a huge bug, and this would get someone dead in IFR conditions in the real world. So, either the runway is mis-marked, or my flux detector needs to be cranked about 10 degrees to the left. Does anybody know if they're working on a fix for this?

Edit: Just tried this in the NTTR map and the runway heading for Nellis appears to be good. Couldn't verify Creech though, didn't even get a backcourse indication on ILS, and I flew straight down 26, needles didn't so much as twitch.

Hi guys,

After reading your posts, I've done a test at Batumi :

DCS latest release

Rwy 13 assigned by ATC (ILS true heading on mission editor map is 125 deg)

Magvar is -6, so I've set my HSI course to 119 deg

On the approach my instruments were perfectly aligned with the designated rwy

I've found no problems here, can you post a track or a video of your approach ?

Regards

Hi bghvp,

I'm just getting into this part of the sim, so I'm not sure where to find the true heading in the mission editor. I'll look for that.

It may be different at Caucases airports, but runway designations, according to FAA regulations, should be within +/- 5 degrees of the magnetic azimuth. With the compass systems and AHRS systems that I work with on a daily basis, I don't think we've ever been concerned with magnetic variation, so having to manually compensate for that doesn't seem right to me for an AHRS. :)

I'm just getting into this part of the sim, so I'm not sure where to find the true heading in the mission editor. I'll look for that.

The Mission Editor shows true headings.

Our virtual instruments show magnetic north. The magnetic variation in the Caucaus region is +6 degrees, as bghvip said. So if the "ruler" tool shows a runway heading of 125, then the magnetic heading would be 119, and this would also be the runway heading given on an approach chart/airport chart.

I believe the runway designations in DCS are static, and it's possible the map is based on a date where magnetic variation had a different value in that region, which is why it's possible that runway designation and runway heading are off by much more than 5°.

Thanks for the info, Yurgon. When I take off from runway 31, my AHRS and compass show 299, so the runway designation should be 30. I understand that the magvar may be out of date for when the runways in the sim were marked, but is the magnetic variation in the sim in sync with current data, while the runways are static? Just curious.

Also, one of the ways we know we've done any good with an AHRS, magnetometer, or compass calibration is by using a known reference. We line up straight down the taxi-way, parallel to 35R, and check the cards to make sure they're showing 350 degrees more or less. Subtracting or adding a certain number of degrees from what is displayed has never been outlined in any procedure, and its never been necessary. Something appears to be out of sync on this. ;)

IIRC, you need to be in 2010-2011 for the MagVar to be correct.

[...] but is the magnetic variation in the sim in sync with current data, while the runways are static? Just curious.

I think so. For example, Skyvector says Kutaisi Kopitnari (aka David the Builder Kutaisi International Airport) Magnetic Variation is currently 6°East.

Also, one of the ways we know we've done any good with an AHRS, magnetometer, or compass calibration is by using a known reference. We line up straight down the taxi-way, parallel to 35R, and check the cards to make sure they're showing 350 degrees more or less. Subtracting or adding a certain number of degrees from what is displayed has never been outlined in any procedure, and its never been necessary. Something appears to be out of sync on this. ;)

I agree, sort of. But looking at a current airport chart/approach chart/departure chart should give runway heading down to a single degree, correct for the current Magnetic Variation.

To put it differently, with an up-to-date airport chart for DCS, runway heading would be correct. For instance, looking at the 476 vFG Georgia Flight Info Pubs 08FEB18 for Batumi, it says runway heading is 120° (with mission date basically in 2011). I believe that chart to be accurate. I also believe that in that case, the runway should be designated 12/30 instead of 13/31, but that's the offset DCS gives us because runway designations are static.

The only time we *actually* need to add/subtract Magnetic Variation from headings is when we measure headings in the Mission Editor or the F10 map, since these are based on True North.

I think, basically we're both trying to say the same thing with different words. ;)

I think, basically we're both trying to say the same thing with different words. ;)

Heh...I think you're right. In almost 26 years of doing what I do, and asking pilots "Did you remember to -----?" when I can't duplicate a squawk, I don't think magnetic variation has ever been part of the question. "Did you remember to turn the thing on?", however, has probably been at the top of the list. The runway I mentioned has always been 35, at least for as long as I can remember. :D

The runway I mentioned has always been 35, at least for as long as I can remember. :D

Airport charts (not sure if all of them) include an annual rate of change. Those that I've seen are typically like 0.1° per year. AFAIK, sometimes runway designations do change due to magnetic variation, but at that rate that's not a common occurence obviously.

Or, to put it in a nerdy way, absence of proof does not equal proof of absence. :music_whistling: :D

Airport charts (not sure if all of them) include an annual rate of change. Those that I've seen are typically like 0.1° per year. AFAIK, sometimes runway designations do change due to magnetic variation, but at that rate that's not a common occurence obviously.

Yup, so a minimum 6 degree change since the runways were marked in DCS, in the amount of time DCS has been in existence, would be an unrealistic amount of change. We're also using a calibrated sighting compass when we do our calibrations, and if we ever saw more than a few degrees off of 350 on our taxi back from the compass rose, we'd know something is still not working the way it should be. :smilewink:

Few things to remember:

Ruler headings are neither true nor magnetic. If they were true headings then dragging the ruler parallel to lines of longitude would show 000°. With the exception of the central meridian of the terrain this isn't true. Up directions are "lines of constant Z" of the XYZ coordinate system.

X-Z zero is 45°07'46''N 340°15'55''E

Grid error near Tbilisi is about 7°

MagVar depends on date and location:

01Jan1900 has E3.8 near XZ 0,0 and E4.5 near Tbilisi

15Jun2000 has E5.0 near XZ 0,0 and E5.2 near Tbilisi and E4.1 western edge

31Dec2100 has E15.3 near XZ0,0 and E13.2 near Tbilisi

Known magnetic headings at features are only as good as the dated charts for specific locations. I don't know if the included kneeboard charts are any good. I'm sure they're plenty accurate for use, 1° off at the most.

The Mission Editor shows true headings.

Nope. Due to the DCS flat world model there's not a single heading that's useable/correct.

It's all a strange mix of mag, true and grid north/heading and there are a lot of threads about this bug/problem.

This coupled with the wrong behaviour with the ILS/FD needles in various planes makes conventional precise navigation/planning in DCS basically impossible.

Eh, if you fly strictly by the primary indicators CDI, GS you'll shoot a CAT I ILS approach just fine. The command bars are not even a requirement to do the procedure in the real airplane. They are a luxury. Stow the bars and fly it like a Cessna.

Eh, if you fly strictly by the primary indicators CDI, GS you'll shoot a CAT I ILS approach just fine.

Nope. Not if your runway markings are 10 degrees off from the magnetic azimuth of the runway as they are in DCS. :smilewink:

Headed up to 11,000 feet for about a week in a few minutes...it'll be nice to get out of these triple digit temps for a little while. Have a good one everybody! :D

Ruler headings are neither true nor magnetic.

Nope. Due to the DCS flat world model there's not a single heading that's useable/correct.

Good to know that the ruler headings in the ME and F10 map aren't True, either. I stand corrected!

Jeez, that sure doesn't make things any easier.

But they aren't. The ILS beams are exactly aligned with the runway. With the bars stowed nothing is amiss.

Due to the DCS flat world model there's not a single heading that's useable/correct.

It's all a strange mix of mag, true and grid north/heading and there are a lot of threads about this bug/problem.

For cockpit instruments in full modules, the F10 ruler reads True bearings.

As far as the A-10C is concerned, the runway/approach heading of Batumi is 126° True.

The magnetic declination at Batumi is approx. +6°E, so the compass in the A-10C cockpit reads 120° Magnetic.

To plan a point to point flight from point A to point B, you'd measure the bearing and distance in the F10 map and subtract the magnetic declination to get the magnetic bearing to fly using the A-10C's instruments.

The AV-8B uses True bearings by default, so the uncorrected F10 bearing is correct for that.

You should not expect to use RL information (Google Earth, SkyVector, etc.) in DCS without checking, for example IRL Batumi RWY 13 is 132°True (126° Magnetic) i.e. different to DCS

True North as used in the cockpit, is not aligned with the Lat/Long grid in DCS, so Lat/Long can only be used for sharing the geographic position of waypoints/targets, not navigation per se.

1.The magnetic deviation at Batumi is approx. +6E, so the compass in the A-10C cockpit reads 120° Magnetic.

2.The AV-8B uses True bearings by default, so the uncorrected F10 bearing is correct for that.

1. And the runway numbers are 12/30...this doesn't fit together.

2. But not IRL I assume, as this would mean that ILS course, VOR, NDB radials and wind info is wrong….

1. And the runway numbers are 12/30...this doesn't fit together.

IRL Batumi RWY 13 is 132°True (126° Magnetic), DCS retains the RL RWY 13 number but not the RL runway bearing as measured via the cockpit instruments.

RL Batumi departure is via RWY 31 (312°True)

2. But not IRL I assume, as this would mean that ILS course, VOR, NDB radials and wind info is wrong….

The in game info is correct for flying in DCS (apart from wind direction which is backwards).

ILS courses, etc. differ from real life, the 476 vFG Flight Info Pubs aren't a collection of RL charts, the 476 vFG, create charts and info based off the real but then adjust them to match DCS's maps/data.

You can't fly real world charts in DCS or vice versa without modification.

If you plan a flight from Batumi to Tiblesi in SkyVector (83° Magnetic for 151nm) and then plan the same flight in the F10 map (82° True (76° Magnetic) for 152nm), you'll find the two routes don't match.

In general, info in DCS given with respect to F10 map 'True' bearings and real life info given as Magnetic.

F10 map 'True' bearings and 'Game Grid' are different names for the same thing but I avoid the term 'game grid' as it sounds like it's about the terrain while in reality it's fundamental to how the cockpit instruments, compass, etc work.

All it'd take, to make things clearer, would be for ED to add a 'True' North/'Magnetic' variation arrow to the F10 map, as I did in my screen capture.