h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: How runways are designated - A795215
Author: Gordon, Keeper of Postal Codes and Maps No One Can Re-fold Properly - U198614

This is referenced in my entry on Ottawa International Airport (currently with a sub).

I'm open to suggestions for improvement.

"dropping the last digit of the compass direction of the runway"

It may be just that I'm more ignorant about such things than your intended audience, but I had a lot of trouble with this part. I kept going "huh? compass directions are letters, not digits - N, S, E, W, NNE, ESE, etc".

It finally clicked that you were talking about dropping the last digit on the degree measurment of a circle. You might want to expand just a bit to explain that?

Okey dokey... I can re-work that bit.

Disclaimer: I'm a geographer so I tend to take things like this for granted.

I've tweaked the entry a bit and added a couple of examples.

Hi Gordon,

I think I was the person who inspired this entry with my dumb question about your entry on Ottawa airport.

Anyway, I'm a sailor (I wrote the entry here on Celestial Nav.) so
1) I should be ashamed at not seeing the pattern between the two numbers.
2) This new entry is perfectly clear to me.


Is there a convention for which way you round?

Some runways do have names. I used to drive a van on an airfield and we would radio the tower to ask "Permission to cross the main" or "Permission to cross the ALD" (Arrestor Landing Deck) But maybe only ground personell used those designations.

Awu.

There is a convention for how you round, which is to the nearest multiple of 10. To further confuse things, because the magnetic North pole moves over time, the compass bearing for a runway can change enough that if you measured it now, the runway designation might be "wrong". But they rarely change the designation of a runway after it's been assigned.

If you had arrestor gear, you were probably working at a military airport, right?

Airport personnel may use some agreed upon terminology when communicating with the ground or tower controllers, especially if there is a uniqueness about the runways, I suppose. Because ground personnel may not necessarily know which end of a runway is the active, they might pick a descriptive name when crossing it, particularly in the middle. When I've heard ground personnel requesting permission to cross a runway at Ottawa, it's usually been at one end of the runway or the other, so they request persmission to cross the threshold of 22, for example.

Grodon,

that was at the back of my mind when I asked about rounding - what if it was, say 005 and you rounded and called it 10, but the yearly changes in declination took it to 4, 3 etc. over time.

You're right, I worked as a Scientific Assistant at the Royal Aircraft Establishment (Naval Air Dept.) We had catapults and arrestor gear although we were as far as you could get from the ocean

Good luck with the entry.

Awu

Excellent entry. (I loved the footnote about the confused pilot being a bad thing)

Question: The true heading also has a pole right? At the north pole both ends of the runway would point south, wouldn't they? Okay, I know there is no runway there, and on the southpole probably neither... Well, it was just a thought.

Do carrier runways also carry these designations?

Just curious.

HELL

The true heading does indeed have a north pole: The North Pole (ie: 90 degrees North). That is not the same as the magnetic North pole which wanders around northern Canada, with a generally westward trend (IIRC). Over the course of a few years, it can move enough that the magnetic declination on a map (the difference between magnetic North and true North) has changed enough to warrant reprinting the maps. (Aviation charts have lines of magnetic declination printed on them.)

If you had a runway that straddled the North pole, I guess it could technically be runway 36T/36T, however I expect they'd designate one end 18T. Upon further thought, they might name one end 01T since that's almost 36T. (Confusing pilots makes unnecessary work for the ground personnel. )

Aircraft carriers do have runway numbers painted on them. I gather the numbers are unique in a fleet, but I don't know much more than that. They don't have any relationship to the direction of landing since they align the ship so the planes land with the wind on the nose.

Thanks a lot.

HELL

Carriers will also steam full power into the wind, to give you more apparent wind over the deck, for both take off and landing. I don't know how the numbers are assigned. (I can try to find out - but I doubt you want that in this entry anyway?)

Nautical charts have a compass rose or more printed on them. Two concentric circles show true and magnetic direction. There is a printed note that says what year the chart was produced and by how much the declination changes per year. Notices to Mariners are used to keep the charts updated, but we can't steer that accurately so a fraction of degree here or there is not important.

I'm not likely to sail that far north, but I think Mercator projection is no longer used above a certain latitude. It's too distorted. A special polar projection is used. I assume that's true for flying too?

Sorry - drifting off topic here.

Awu.

In North America, different projections are used depending on the scale of the chart. Canadian topographic maps have a magnetic declination correction factor printed on the map. It tells you the difference between magnetic North and true North at the time of the printing along with an annual drift factor that you can use to calculate the difference when you're using the map.

There are probably some maps for aviators flying polar routes that are in a polar projection, though I'm not sure.

"The numbers are derived by rounding the compass bearing of the runway from one end to the nearest ten degrees, dropping the last digit and putting a zero on the beginning if it would be a single digit. Thus, one number is the reciprocal of the other. If a runway is aligned North-South, then it is 18/36, not 00/18."

I think you're missing a sentence here. Before 'Thus', there should be something to the extend that degrees/numbers roll over from 360 to 1 (or 36 to 01, respectively). This rollover is a modulo operation, not a recipro-something (). The numbers in a pair differ by 18 (eg: 02/20), they are opposite on a circle running from 01 to 360 and they denote opposite directions.

Hmmm... I think you're right. I'll have to re-write that paragraph to fill in the sentence before the "thus". Thanks for pointing that out.

Oh, and when talking about compasses, the reciprocal of a heading is the other end of the needle (i.e. 180 degrees away).

Hmmm... right maybe you should include that small difference (reciprocal and 'complementary' in different jargons)

I think that entry could be good to go as soon as you made those little changes.

- I was sooo close to pushing that recommend button -

HELL

Hi Hell,

Gordon and I had that same discussion over on the Ottawa Airport thread. So I agree that since we are all stumbling over it (Bossel too - above), it might need a foot note or brief explanation.

Awu.

exactly, and as soon as that's clear it would be ready for inclusion IMO.

HELL

Ok, footnote added.

I can see I'm going to have to write an entry about this and put it in my university project.

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