Runway numbers

[Merik]

I'm not sure if I get it right, but it seems to me that a runway is named 12R when it's direction is on 120 degrees; also, if the same runway is going to be used in the reverse direction, its name should become 30L. Am I getting this right? And if yes, where can I read more about these naming conventions?

[Gijs]

Correct!
A nice explenation can be found at the BBC website: http://www.bbc.co.uk/dna/h2g2/A810145

[sim]

Spot on Merik,
12 is 120 degrees its reciprocal is simply 12 + 18 = 30. Like runway 03 is 30 degrees and reverse direction is 03 + 18 = 21 etc etc. Runway directions are set at 10 degree intervals so we ignore the correct maths of 180 and add (or subtract) 18 as any variation under 10 is not counted. Don't forget though to add the final 0 for navigation purposes as mistakenly following 030 instead of 300 degrees will land you in the soup!!
Cheers, sim

[Tuxklok]

Also remember runway numbers are rounded, the real heading could be a number of degrees in either direction. Rarely is runway 30 exactly 300 degrees for example..could be 303, 296, etc, etc.

cheers

[MAKG]

Except if you're at KSQL.

Then, heading 130 is 31 and 310 is 13.

Well, at least that's what FG says....

[sim]

No wonder my navigation takes me to exotic places. All the airport runways are giving my compass fix way-out readings!
Cheers, sim

[nickyivyca]

Except if you're at KSQL.

Then, heading 130 is 31 and 310 is 13.

Well, at least that's what FG says....

And at KPAO! Odd...

Runways do use magnetic heading, not real heading-make sure to keep that in mind, it's very important! Magnetic heading varies between place though, while EGLL in London will have a 9/27 for a horizontal runway, the horizontal runway at KBUR near LA is 8/26, and the busiest runway for landings at KORD in Chicago, which is horizontal, is 10/28. Then look at KSFO, where the 10/28s are nearly diagonal, and the perpendicular 1/19s are perpendicularly diagonal.

[Merik]

Thanks for the reply; I'm assuming that, by putting emphasis on the use of magnetic headings, you mean that in most other cases, we use the geographical headings, right?

Also, is the differences you mentioned because the magnetic poles are deviated from geographic poles, or is this because the magnetic poles are not antipodal (i.e. the Earth's magnetic field is not symmetric)?

[sim]

All of the above Merik except like runway numbers magnetic headings tend to be prefered for air nav over geographical headings as explained below,
Aviation sectionals (maps / charts) and databases used for air navigation are based on True north rather than magnetic north, and the constant and significant slight changes in the actual location of magnetic north and local irregularities in the planet's magnetic field require that charts and databases be updated at least 2 times per year to reflect the current magnetic variation correction from True north. For example, as of March 2010, near San Francisco the magnetic north is about 14.3 degrees east of True north, with the difference decreasing by about 6 minutes of arc per year.

When plotting a course, a pilot in most small planes will plot a trip using true north on a sectional (map), then, convert the true north bearings to magnetic north for in-plane navigation use (which rely on cockpit instruments that read magnetic north).

Radionavigation aids located on the ground, such as VORs, are also checked and updated to keep them aligned with magnetic north to allow pilots to use their magnetic compasses for accurate and reliable in-plane navigation

GPS systems used for air navigation can use magnetic north or true north. In order to make them more compatible with systems that depend on magnetic north, magnetic north is often chosen, at the pilot's preference. The GPS receiver natively reads in true north, but can elegantly calculate magnetic north based on its true position and data tables calculate the current location and direction of the north magnetic pole and (potentially) any local variations, if the GPS is set to use magnetic compass readings.
WikiP on air nav. Cheers, sim