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View Full Version : ILS: needle someimes does not line up with runway direction



freddy
03-21-2010, 06:36 PM
When flying ILS, sometimes the needle does not line up with the runway direction. This is with stock FSX airports. No add-ons.

An example: ATC advises the runway in use is ILS runway 01. Using the course selection knob, I dial that course in and set the Nav receiver for the selected ILS frequency. On descent, I fly heading 01 and keep the needle pointed straight up and down; making adjustments to keep the centre needle in the middle on the localizer. BUT, despite being runway 01, the runway is not always lined up perfectly with the needle. If I keep this needle pointed straight up and fly this heading to the ground, I will land at an angle to the runway. Sometimes this angle is very slight; other times it is quite pronounced. It is as if the runway is actually runway 01-and-a-half; or in some cases, should be runway 02.

Note that I am aware of factors like the wind. I am not talking about crabbing here. Assume zero wind. And I am not talking about gyro shift (I adjust for that pressing the "D" key). I am talking about the fact that runway 01 in my example does not match heading 01.

I hope I am describing this properly.

In worst cases, the needle is in fact perfectly lined up with the runway, but it is off to the left or the right of the runway .... meaning that following it will have me landing on the grass, perfectly parallel to the runway. (I do understand that the localizer beam is not transmitting from the end of the runway, but is coming from an antenna off to the left or right of the runway - but sometimes it seems like the beam is so far off that it could be another runway altogether.)

Is this normal in the real world? How does one land in low visibilty when one "follows the needles" only to find the runway is off at a slight angle?

Or, is this really just a "guide" to get you "close enough to see the runway" whereupon you are expected to adjust to line up?

ronzo155
03-21-2010, 06:51 PM
The ILS transmitter is not set in the middle of the runway. It is, of course off to one side. And, yes, it is assumed that you will manually fly the plane onto the threshold after

you see the runway. You cannot fly in poor visibility weather, if you do not fly IFR.

I think FSX will forbid you to take off or land if you are flying VFR.

When flying the ILS, you need to be in APP mode, not NAV mode.
In APP mode, the aircraft will "lock" onto the localizer, and then automatically decend when you cross the Glide Slope.
The ILS is set up so the Autopilot will fly the aircraft to the threshold of the runway in poor visibility.
Try starting at about 20 miles from the runway, with the NAV1 radio set to the ILS frequency.
If you are doing an IFR flight, ATC will vector you to an intercept course with the ILS. All you have to do is have your NAV1 set to the ILS freq.
You are doing a lot more work than you need to.

ReggieF5421
03-21-2010, 06:58 PM
It would help to know which airport(s) are giving you a problem and which aircraft are giving you a problem.

You should also know that by default all the localizers in FS have the backcourse enabled. Something which is not true in the real world.

Also, there are a fair number of places in the world which do not have an ILS localizer lined up with the runway for various reasons. Most of these are Offset Localizers.

I don't remember the exact number, but I think it was 3 degrees, which is the amount which an ILS may be aligned at an angle to the runway and still be an ILS.

While FS will display soon ILS as a CAT II or CAT III, all the ILS in FS work exactly the same.

Many ILS in FS represent airports where you have to disengage the autopilot several hundred feet above the runway and up to a mile from the runway - and make the final alignment/ descent manually.

I might also mention that FS has a limitation on the ILS behavior. You must be below the Glide Slope to engage it, flying into the beam. Capturing the Glide Slope when high almost never works in FS.

zolteck
03-21-2010, 07:00 PM
The localizer is generally placed about 1000ft off the end of the runway down the centerline,depending on runway lengh. that will give you a full scale deflection of about 350 ft to the right or left at the runway threshold. as far as it " really just a "guide" to get you "close enough to see the runway" whereupon you are expected to adjust to line up? " that is true only to the point that for a localizer to be considered a localizer it has to be within 3 degrees of the runway centerline. When you exceed that 3 degree angle it's called an Localizer Directional Aid (3 to 6 degrees wide) or a simplified directional facility (6 to 12 degrees wide). you are expected to adjust to line up if the rw is visible at the Decision Height. That is also the reason if you have no GS to follow you want to reach the minimum descent altitude as soon as possible

freddy
03-21-2010, 07:02 PM
I am familiar with setting up and flying the ILS approach, dialing in the frequencies, following ATC's instructions, being vectored, intercepting, etc. That part I have no troubles with.

However, it has been mentioned that I should be set in APP mode. Hmmm, I am not doing that. I keep it in NAV mode. Is that my issue here? APP mode as opposed to NAV mode? I do understand that in this mode the aircraft will "lock" onto the localizer and then automatically decend when I cross the Glide Slope ... but I figured that AFTER THAT has occured APP would just be similar to and work like NAV and the runway would still be off at an angle. Am I wrong with that thinking? Is APP mode "more accurate" for the ILS than NAV?

3 degrees huh? OK, that makes a bit of sense to me.

I do not have any add-on aircraft, this is all with stock FSX aircraft only. An example airport might be Townsville airport, Australia (YBTL).

I am comfortable flying IFR, and can fly with no problems in IMC ... bad visibilty, fog etc, are all no problem. I've just find it frustrating that I line up the needles and the runway is off. But, if it is supposed to like that, with 3 degree margin, then that is OK. I suppose that is what I am looking for here.

Not to mention that visibility depiction in FSX is not perfect making it extrememly difficult to "see" the runway in some cases, whereas in the real world you would probably be seeing the runway a lot sooner.

ReggieF5421
03-21-2010, 07:15 PM
If your only problem is that when you manually fly the approach the needle might lead you to be off course by a few degrees, correct?

Again, need to know specific airports.

As mentioned above an ILS will not always exactly line up with the runway in the real world. In some cases in FSX the ILS is misplaced or misaligned. Those are few though.

Re the mode.

NAV mode looks at the ILS as a VOR. It does not line you up with the signal/ radial. It only points you directly at the transmitter.

If you line up for course 010, the ILS heading for the runway 01 might be 006 or 014 or anything between. There is a 10 degree window for each runway number. You need the magnetic heading of the localizer to be exact.

APP mode tells the autopilot that the signal is an ILS and that the aircraft must be aligned to follow the directional signal. The NAV mode requires you the pilot to make the alignment manually.

Depending upon the aircraft and instrumentation, the Glide Slope may show while in the NAV mode and may not.

Some ILS are setup like Rwy 12 at MKJP where there is no room at the end of the runway for the localizer. So it is built off to the side of the runway, and pointed at a slight angle. At decision height, the aircraft following the ILS perfectly will be in position to make a slight turn to the left and align with the runway manually.

f16jockey_2
03-21-2010, 07:17 PM
ATC advises the runway in use is ILS runway 01.
Once advised on this, check the map for the real ILS heading for that rwy. Rwy numbers are rounded to the closest that can be divided by 10 (sorry for my crappy English).
A rwy 01 can be headed from about hdg 005 to 015 (not sure where the limits are).
Less than hdg 005 becomes rwy 36 (since there's no such thing as Rwy 00), higher then 015 is rwy 02.
[EDIT] Sorry for this, Reggie just answered about the same...

Greetz,
Wim

freddy
03-21-2010, 07:29 PM
Reggie, your detailed explanation is painting the picture perfectly for me. And f16jockey clarifys.

I am aware that (in the real world) there are places where there is no room at the end of the runway for the localizer and it is built off to the side of the runway as a result. I was also aware that in FSX there are a handful of airports where the ILS is misplaced or misaligned. These aren't the issues here.

Yes, my problem is that when I manually fly the approach, the needle might lead me to be off course by a few degrees. With the responses provided here, I can see now why that is.

I am glad to learn that NAV mode looks at the ILS as a VOR and does not line me up with the signal/radial. It's only pointing me directly at the transmitter. OK. That does make sense. Quite logical really, now that I think about it.

If you want an example of a specific airport, Townsville (Australia) was where I flew to last night. YBTL. Fogged in badly (due to a cyclone to the south). Visibility down to 2nm. Stock FSX 737. Runway was off enough to be frustrating. At 2nm, when the runway appeared out of the fog (quite suddenly due to the graphics limitations of FSX), I was not lined up - no chance to correct - and had to fly missed. I missed again on the second approach (same reason). So I diverted to Cairns (further north) and landed fine. But all of this posed this question.

Thanks to all who have responded. I think I now have a more clear picture of this. Especifically NAV versus APP. And that, yes, it is OK for the runway to be off by a few degrees. At least I know that I am not doing anything wrong per se.

ReggieF5421
03-22-2010, 12:05 AM
You picked one of the strange ones.

YBTL has runway 01/19 but the magentic heading for Rwy 01 is 016 degrees in FSX.

The default FSX data comes from April 2005. A Google Earth image of the airport dated July 15, 2009 shows the runway is numbered 01/19.

World Aero Data shows the runway is numbered 01/19.

The FSX data has the airport and the ILS true headings at 24.0600 degrees with a deviation of 8 degrees - so the FSX runway magnetic heading is 016 degrees and the ILS approach heading is 016 degrees magnetic. The Localizer is correctly aligned with the runway, and the default ILS approach data is correctly aligned with the runway.

The FS2004 data is from Sept-Oct 2002. It also shows the runway and ILS both at 024.06 degrees true and the deviation of 8 degrees. The FS2004 magnetic heading for the runway and ILS approach is 016 degrees.

I have no idea why the airport runway designator has not been changed to 02/20, especially since it has apparently been on that heading for over 7 1/2 years.

scott967
03-22-2010, 12:10 AM
I am glad to learn that NAV mode looks at the ILS as a VOR and does not line me up with the signal/radial. It's only pointing me directly at the transmitter. OK. That does make sense. Quite logical really, now that I think about it.


NAV and APP modes both will operate with VOR, LOC (ILS) or GPS guidance. The difference is the sensitivity to deviations (APP is more sensitive).

scott s.
.

freddy
03-22-2010, 10:04 PM
Reggie,

Very interesting. I chose "one of the strange ones". Hehe, no wonder I had questions. :) Thanks for your excellent insights on this ... and thanks for the "extra" research as well.


scott967,

Now that you mention it, I do seem to recall that I read that somewhere (that APP was more sensitive). Hmmm, it might have been in the "Microsoft Flight Simulator X For Pilots Real World Training" book. With flying, there's a lot to pack in to one's head ... and every now and then these things can get forgotten. "If you don't use it, you lose it". Which, considering I've been using NAV mode for ILS approaches, holds true for me with regard to APP mode.

uafzach
03-22-2010, 10:54 PM
It would help to know which airport(s) are giving you a problem and which aircraft are giving you a problem.

You should also know that by default all the localizers in FS have the backcourse enabled. Something which is not true in the real world.

Also, there are a fair number of places in the world which do not have an ILS localizer lined up with the runway for various reasons. Most of these are Offset Localizers.

I don't remember the exact number, but I think it was 3 degrees, which is the amount which an ILS may be aligned at an angle to the runway and still be an ILS.

While FS will display soon ILS as a CAT II or CAT III, all the ILS in FS work exactly the same.

Many ILS in FS represent airports where you have to disengage the autopilot several hundred feet above the runway and up to a mile from the runway - and make the final alignment/ descent manually.

I might also mention that FS has a limitation on the ILS behavior. You must be below the Glide Slope to engage it, flying into the beam. Capturing the Glide Slope when high almost never works in FS.

I had this problem at KHWD ILS RWY 28L. It was off pretty far, usually I just switch to the GPS to correct my flight path... It is annoying..

RyanbATC
03-22-2010, 11:26 PM
And we're certain this was not an offset localizer?

ReggieF5421
03-23-2010, 12:26 AM
I had this problem at KHWD ILS RWY 28L. It was off pretty far, usually I just switch to the GPS to correct my flight path... It is annoying..

As Ryan noted - KHWD does not have an ILS - it has an offset localizer LOC/DME for Rwy 28L.

In the United States it is easy to find airport approach charts on-line for free. Here is the chart for KHWD http://204.108.4.16/d-tpp/1003/05015LD28L.PDF

Personally I go to www.airnav.com and check the airport page, but their are several other websites with offer the charts.

They all link back to the FAA site.

I just find AirNav easier to find the specific airport, and many of the additional notes are useful.

However when using real world charts, you must remember that FSX approach and navigation data is almost 5 years old. The charts may not match FSX.

The localizer at KHWD is offset to the north of the runway and is offset by a little over 3 degrees. the runway in FSX is 299.920 degrees and the localizer is set to 303.00 degrees - a difference of 3.08 degrees.

I've attached a screenshot from ADE - Airport Design Editor - which shows the runway and localizer. The approach following the localizer requires you to manually align with the runway. The localizer does not have a Glide Slope - so vertical navigation is the pilot responsibility. I've also attached a screenshot of the actual airport from Google Earth - which shows the localizer is offset and correctly placed in FSX.

freddy
03-23-2010, 03:27 AM
And we're certain this was not an offset localizer?

Ahh. A good question. Here's the chart for Townsville (YBTL). It clearly shows 16 degrees.

http://img716.imageshack.us/img716/6440/townsvilleils.jpg (http://img716.imageshack.us/i/townsvilleils.jpg/)

Teamski
08-07-2011, 05:26 PM
I know this is pretty late, but I am finding more and more airports with misaligned ILS approaches. If you want a good example, Runway 23 at MacDill AFB (freq 111.70, heading 228 true) is about 200 yards left of the runway. This cannot be correct, and it is really frustrating as I almost landed in trees insteads of a runway during a 0-0 approach at Volk. Any ideas of a fix? I can't believe that this has not been a major issue with the game.

-Ski

mallcott
08-07-2011, 06:33 PM
I know this is pretty late, but I am finding more and more airports with misaligned ILS approaches. If you want a good example, Runway 23 at MacDill AFB (freq 111.70, heading 228 true) is about 200 yards left of the runway. This cannot be correct, and it is really frustrating as I almost landed in trees insteads of a runway during a 0-0 approach at Volk. Any ideas of a fix? I can't believe that this has not been a major issue with the game.

-Ski

No, it is more a misunderstanding on your part of the variation and types of localizer. They do not all line you up with the runway, some are offset laterally but have the same heading as the runway. Others are angled off the runway centreline.

Lots still to learn!

jvile
08-08-2011, 06:16 PM
I know this is pretty late, but I am finding more and more airports with misaligned ILS approaches. If you want a good example, Runway 23 at MacDill AFB (freq 111.70, heading 228 true) is about 200 yards left of the runway. This cannot be correct, and it is really frustrating as I almost landed in trees insteads of a runway during a 0-0 approach at Volk. Any ideas of a fix? I can't believe that this has not been a major issue with the game.

-Ski

Ski

Did that airport change runway numbers from 4/22 to 5/23?

I have a file that fixed the offset problem. The runway Localizers are still offset as per current charts but FS9 and FSX misplaced the Localizer antennas which causes the problem.

My file is based on these statements

http://img850.imageshack.us/img850/2479/fsscr007w.jpg (http://imageshack.us/photo/my-images/850/fsscr007w.jpg/)

http://img38.imageshack.us/img38/5848/fsscr008u.jpg (http://imageshack.us/photo/my-images/38/fsscr008u.jpg/)

I need to change the runway numbers if they are now 5/23 but current charts still say 4/22

jim