Understanding runway numbers

[xvii-Dietrich]

I'm trying to figure out nomenclature for runways. From what I gather, there is a "number" for the runway, which is the heading of that runway, to the nearest 10 degrees, and then shown without the last 0.

Thus, a runway with heading 076 degrees, would be rounded up to 080 and then shown as "08". Then the number of the runway for the other direction (i.e. exactly same physical runway, but approaching it from the other direction) would be, to use the same example 256, rounded to 260 and thus shown as "26". So far so good.

Where is then gets confusing, is that there seems to be a difference between runways listed by "true north" heading and those listed by "magnetic north" heading. For instance, the AFBs-for-CLOD (LINK) seems to use true north. However, other references seem to use magnetic north. From a flight point of view, the magnetic makes more sense, as it would then be easier to check when taking off or landing.

I tried checking some examples and found, for instance, comparing the AFB to the Satellite image (i.e. Google Maps Satellite Image) I found the following:

AFB	Sat.Img	Name
12/30	13/31	Caen Carpiquet
06/24	07/25	Creil
02/22	05/23	Le Hvre Octeville
02/20	03/21	Biggin Hill
05/23	06/24	Rochford

This seems to be just the magnetic offset. On the other hand for Kenley they were identical.

What I'm wondering is what should they really be?

And is the discrepancy due to a change in the system (i.e. during WWII they used true north, whereas today they use magnetic north or something)?

[Decay]

Magnetic Headings drift over the years.

Runway Headings are based on magnetic headings.

[Baffin]

Put "runway numbers" into your internet search engine and you will find all the information you ever wanted, and a lot more! Suffice it to say that if it's on an airport or reported by the control tower, it's a magnetic reference. They are never "rounded" incorrectly, but over time, the Earth's magnetic field changes so that a numerical reorientation may be required by NOAA and the FAA. When that happens, they will renumber the runways and reissue all the airport diagrams, approach charts, etc.

[ATAG_ProArmis]

..............

Where is then gets confusing, is that there seems to be a difference between runways listed by "true north" heading and those listed by "magnetic north" heading. For instance, the AFBs-for-CLOD (LINK) seems to use true north. However, other references seem to use magnetic north. From a flight point of view, the magnetic makes more sense, as it would then be easier to check when taking off or landing.

I tried checking some examples and found, for instance, comparing the AFB to the Satellite image (i.e. Google Maps Satellite Image) I found the following:

AFB	Sat.Img	Name
12/30	13/31	Caen Carpiquet
06/24	07/25	Creil
02/22	05/23	Le Hvre Octeville
02/20	03/21	Biggin Hill
05/23	06/24	Rochford

This seems to be just the magnetic offset. On the other hand for Kenley they were identical.

What I'm wondering is what should they really be?

And is the discrepancy due to a change in the system (i.e. during WWII they used true north, whereas today they use magnetic north or something)?

From my point of view you probably mixed up something:

1. AFB = Airforce base -for ex. AFB-No. for Biggin Hill in CLOD is EGKB (not 02/20)
2. RWY = Runway - (one of) the RWY-name(s) of Biggin Hill is "02/20 (only a name not more)" ...and of course this name belongs to the RWY-direction... here it is 023 - 203. RWY-Name and RWY-direction are only facts and having basicly nothing to do with "true north" or "magnetic north". In many cases the headings of runways based only on average ratios of local winds or other local tarrain conditions (s. following LINK).

How to plan a britisch Airport (Flight 1929)

Sure, the given RWY-direction is helpful to set up the gyro direction, but this is a different thing (s. also Link below)

Magnetic Compass (Flight 1943)

I hope it helps a bit

[Baffin]

I can only speak to the way things are now, not as the were during WWII:
-OP's reference to AFB is the title of a document referenced by his link. The author liked AFB as an abbreviation.

-EGBK is an ICAO (International Civil Aircraft Organization) identifier for the airport. Even Military fields have ICAO identifiers, although they may also have identifiers assigned by the home nation. Example: "WRI" is McGuire AFB, New Jersey, USA to US agencies, but ICAO "KWRI" is used in an international flight plan. Same place, different codes.

-The name of the runway refers to it's closest magnetic heading at the time the document you are reading was released for navigation. "35/17" indicates a piece of concrete with a magnetic heading 350 and it's reciprocal heading. It is rounded to the nearest 10 degrees. In areas where there is large magnetic variation (ex: Thule AB, Greenland) the runway may be depicted and/or referred to in true north terms to avoid confusing pilots. (Which it invariably does anyway!) Magnetic runway headings change as the Earth's magnetic field varies as time passes.

-The US FAA's Airman Information Manual (available online) describes all these things in detail and is a reliable source of correct information regarding current air operations in the US and is accepted by nearly all nations:
http://www.faa.gov/air_traffic/publi...ic_4-03-14.pdf

[ATAG_ProArmis]

.....

-The name of the runway refers to it's closest magnetic heading at the time the document you are reading was released for navigation. "35/17" indicates a piece of concrete with a magnetic heading 350 and it's reciprocal heading. It is rounded to the nearest 10 degrees. In areas where there is large magnetic variation (ex: Thule AB, Greenland) the runway may be depicted and/or referred to in true north terms to avoid confusing pilots. (Which it invariably does anyway!) Magnetic runway headings change as the Earth's magnetic field varies as time passes...

That s is nearly what I meant. By the time the magnetic headings was used. But the RWY-Name and the final -direction is only the result of a previous planning process (and not a indicator for true- or magnetic heading). And if you compare the status between 1939-1945 and now, the change of the Earth magnetic field is somewhere around 10 degrees. Don t know if this is really relevant for flying in CLOD. For the first adjusting of the gyro direction I personal take the runway heading as depicted in the map (as far as I can see what current runway I am..lol)

Anyway..interesting Thread..many thanks xvii-Dietrich

[Roblex]

The actual runway at Biggin is '03/21', i.e. that is what it is called in the real world. The others are correct. I have always assumed that whoever designed the Clod base just made a mistake.

[xvii-Dietrich]

Firstly, thanks everyone for the replies. Very informative and much appreciated. Inspired by this, I went and did a lot of reading and some experiments and, somehow, I am now even more confused that before.

What I did was to firstly pick a runway, in this case Caen Carpiquet.

I loaded up the missions editor, zoomed in, took a screenshot and then using a graphics editor measured the angle of the runway. It was 121 degrees. Now, I understand that the map is in "true-north" orientation, so that means that the true-north bearing of this runway is 121 degrees. Fine.

According to various geophysical references, the magnetic variation for 1940 for the English Channel area is -10 degrees. That is, to get true bearing from compass bearing, you subtract 10.

runway4.png

Another way of thinking of this is that the magnetic compass reading is 10 degrees more than the true direction. So, if I was perfectly lined up on the runway at Caen Carpiquet, my compass would read 121+10 = 131 degrees.

What that would mean, then, is that the runway number would be 13.

So, I have a look at the AFB document and it shows the following...

runway1.png

Yes, this is the true bearing (assuming that the map is true north oriented). Puzzled I then made a critical mistake.

I did an experiment.

Here's what I did. I opened up the mission editor...

1. If the runway is 121 degrees true, then a plane lined up on the runway should have a magnetic compass reading of 131.
2. I then placed a marker exactly on the far corner of the runway.
3. I took a Ju 88 and perfectly lined it up on the edge (no mean feat for me!)
4. I then sighted through the Lotfe bombsight to ensure that the alignment is absolutely perfect.
5. I then waited for the compasses to settle and read them off.

runway_heading_test.png

For the Ju 88, the magnetic compass read 120 degrees. The repeater compass read 122 degrees.

I repeated the test a few times with different Ju 88s and got the same result each time. I would say my error is +/- 0.5 degrees. By the way, in doing so, I calibrated the horizontal markings on the Lotfe. They seem to be about 1.25 degrees each. That is the 4 ticks to the right gives you a 5 degree aircraft yaw.

Puzzled I then did the same experiment with an He 111. This time I got magnetic compass reading of 122 and repeater compass reading of 124.

Again, this was repeatable, and I estimated my measurement accuracy to +/- 0.5 degrees.

That implies that the map is on magnetic alignment. However, I don't believe that is the case either. In a separate test, I very carefully flew a long range calibrated navigation mission.

ju88_navigation_01.jpg

I did a very careful analysis of this (ask me if you want the long and painful details) and reckon that the map is "true" to within 0.5 km over 320 km. I was also able to explain the 1 degree drift due to a quantisation error in my calibration process. Thus, with compass and Kurssteuerung, I believe that micro-precision flying is possible.

So why the runway anomaly?

*weep*

The only thing I can think of is that it has something to do with the fact the aeroplane is not level, but is leaning back on its tailwheel. Perhaps it is only when the aircraft is perfectly level that the compasses are correct (although I note that the repeater compass never matches the magnetic compass anyway).

Okay, so let's then make this worse. Leaving IL-2:Cliffs of Dover aside and considering the real world (apparently this exists), I checked the modern Caen Carpiquet airfield.

There is a runway there at 125.3 degree true bearing. According to the current 2014 magnetic deviation, this is measured at negative 0 deg 52 min (= 0.8667 deg)

runway2.png

And that would mean that the magnetic bearing of this runway is 126.2 degrees. Round up and leave of the last zero and the runway number should be 13.

runway3.png

*eye-twitch*

[Baffin]

Firstly, thanks everyone for the replies. Very informative and much appreciated. Inspired by this, I went and did a lot of reading and some experiments and, somehow, I am now even more confused that before.

What I did was to firstly pick a runway, in this case Caen Carpiquet.

I loaded up the missions editor, zoomed in, took a screenshot and then using a graphics editor measured the angle of the runway. It was 121 degrees. Now, I understand that the map is in "true-north" orientation, so that means that the true-north bearing of this runway is 121 degrees. Fine.

According to various geophysical references, the magnetic variation for 1940 for the English Channel area is -10 degrees. That is, to get true bearing from compass bearing, you subtract 10.

runway4.png

Another way of thinking of this is that the magnetic compass reading is 10 degrees more than the true direction. So, if I was perfectly lined up on the runway at Caen Carpiquet, my compass would read 121+10 = 131 degrees.

What that would mean, then, is that the runway number would be 13.

So, I have a look at the AFB document and it shows the following...

runway1.png

Yes, this is the true bearing (assuming that the map is true north oriented). Puzzled I then made a critical mistake.

I did an experiment.

Here's what I did. I opened up the mission editor...

1. If the runway is 121 degrees true, then a plane lined up on the runway should have a magnetic compass reading of 131.
2. I then placed a marker exactly on the far corner of the runway.
3. I took a Ju 88 and perfectly lined it up on the edge (no mean feat for me!)
4. I then sighted through the Lotfe bombsight to ensure that the alignment is absolutely perfect.
5. I then waited for the compasses to settle and read them off.

runway_heading_test.png

For the Ju 88, the magnetic compass read 120 degrees. The repeater compass read 122 degrees.

I repeated the test a few times with different Ju 88s and got the same result each time. I would say my error is +/- 0.5 degrees. By the way, in doing so, I calibrated the horizontal markings on the Lotfe. They seem to be about 1.25 degrees each. That is the 4 ticks to the right gives you a 5 degree aircraft yaw.

Puzzled I then did the same experiment with an He 111. This time I got magnetic compass reading of 122 and repeater compass reading of 124.

Again, this was repeatable, and I estimated my measurement accuracy to +/- 0.5 degrees.

That implies that the map is on magnetic alignment. However, I don't believe that is the case either. In a separate test, I very carefully flew a long range calibrated navigation mission.

ju88_navigation_01.jpg

I did a very careful analysis of this (ask me if you want the long and painful details) and reckon that the map is "true" to within 0.5 km over 320 km. I was also able to explain the 1 degree drift due to a quantisation error in my calibration process. Thus, with compass and Kurssteuerung, I believe that micro-precision flying is possible.

So why the runway anomaly?

*weep*

The only thing I can think of is that it has something to do with the fact the aeroplane is not level, but is leaning back on its tailwheel. Perhaps it is only when the aircraft is perfectly level that the compasses are correct (although I note that the repeater compass never matches the magnetic compass anyway).

Okay, so let's then make this worse. Leaving IL-2:Cliffs of Dover aside and considering the real world (apparently this exists), I checked the modern Caen Carpiquet airfield.

There is a runway there at 125.3 degree true bearing. According to the current 2014 magnetic deviation, this is measured at negative 0 deg 52 min (= 0.8667 deg)

runway2.png

And that would mean that the magnetic bearing of this runway is 126.2 degrees. Round up and leave of the last zero and the runway number should be 13.

runway3.png

*eye-twitch*

All magnetic compasses suffer from "Dip" error. The north pole needle points down towards the Magnetic pole on the earth's surface and is most pronounced when pitch or roll is introduced. Here's some FAA explanations on compass errors:

www.faatest.com/books/ifrh/4-8.htm