The worldwide ICAO regulation defines runway directions with the magnetic north. Makes sense as GPS is not considered safe enough for main navigation, it's only here for additional help (in theory at least). Also traditional radio navigation (VOR, NDB) is done with magnetic directions. Changing runways directions happens sometimes, it's not such a rare event, as the north is moving on many parts of the globe (not everywhere the same though). I know of a few places here that have changed runway direction.
Anyway, it's not that much of a burden, because there is a very defined and safe process for updating airport and airspace data. When that type of change happens, udates are shipped over many channels that pilots should follow.
Imagine you're flying the landing pattern in a cloud. You just flew through a thermal boundary so your battery jostled and lost voltage for a split second, resetting your electronics that require a >5 minute reboot and config time. How do you determine geographic north?
And whatever you do, don't forget your manual compass deviation rules: accelerate north, decelerate south
Trivia note: I believe the standard compass is called a "whiskey compass". Not sure why. Probably because if that's all the nav gear you got working you'll probably be using copious quantities of whiskey after landing. (Actually if memory serves I believe the early compasses floated in whiskey. No doubt this practice did not last very long. I think they use kerosene now)
The explanation I have read is that it is a "wet compass" (a ball floating in liquid), which was abbreviated "W compass", which is pronounced "whiskey compass" in the NATO phonetic alphabet that pilots use. I doubt whiskey was ever used to fill them, since even water would have worked better in terms of cost, transparency, evaporation, or boiling point.
I was aiming for tone, not accuracy. There are all sorts of topics that pilots discuss with great vim and vigor. I was trying to convey that feeling. Looks like I missed the boat.
Isn't that the same problem though? Easier from them to do one calculation on the ground in advance rather than pilots having to worry about a conversion in the air.
ICAO VFR maps contain the magnetic deviation as information - you just have to apply it to all your directions and be able to remember in what direction you have to correct ;) Not so trivial under stress. Anyway, on US and EU latitudes, the difference is not much bigger than 2 or 3 degrees, right?
yellowbkpk explained one reason: we fly with magnetic compasses, so we need the runways to be magnetic as well.
Even if we could come up with a safe and reliable way to always have true heading displayed in the cockpit, there remains a very pragmatic reason for keeping runway numbers magnetic rather than true: under the current system, we have to change a few runways every once in a great while; if we switched systems, we would have to change every runway in the whole world all at once. It's not just a simple matter of re-painting the runways: publications have to be changed, notices have to be issued, etc. Changes would cascade out into literally every aspect of the aviation industry.
No, they'd still have to be swapped (under the current scheme of runway numbering). If you're landing on runway 18, you know your compass better be reading ~180° (after correction for deviation). Similarly, when taking off from runway 18, your compass should read the same.
I've heard, although I can't find confirmation of it at the moment, that this has happened on occasion at airports in Alaska where, being much closer to the pole, the heading to magnetic north is changing more rapidly.
Except that the essential description of a runway is its direction. It would be a lot more painful if you had to look up the direction of every runway.
It's not a "name". That number is the meaning. The number represents the "points on the compass" as it were. Since the "compass" is changing, the numbers have to change.
I find it interesting that they don't use true north though.
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[ 2.8 ms ] story [ 72.8 ms ] threadAnyway, it's not that much of a burden, because there is a very defined and safe process for updating airport and airspace data. When that type of change happens, udates are shipped over many channels that pilots should follow.
Trivia note: I believe the standard compass is called a "whiskey compass". Not sure why. Probably because if that's all the nav gear you got working you'll probably be using copious quantities of whiskey after landing. (Actually if memory serves I believe the early compasses floated in whiskey. No doubt this practice did not last very long. I think they use kerosene now)
Just trying to share a little FBO-lore. It's common to tell the whiskey compass story in the fashion I have. http://iflyasa.com/2009/10/11/whiskey-compass/
I was aiming for tone, not accuracy. There are all sorts of topics that pilots discuss with great vim and vigor. I was trying to convey that feeling. Looks like I missed the boat.
http://en.wikipedia.org/wiki/File:IGRF_2000_magnetic_declina...
Even if we could come up with a safe and reliable way to always have true heading displayed in the cockpit, there remains a very pragmatic reason for keeping runway numbers magnetic rather than true: under the current system, we have to change a few runways every once in a great while; if we switched systems, we would have to change every runway in the whole world all at once. It's not just a simple matter of re-painting the runways: publications have to be changed, notices have to be issued, etc. Changes would cascade out into literally every aspect of the aviation industry.
You can see just how much the magnetic variation changes around the world in this graphic: http://en.wikipedia.org/wiki/File:Earth_Magnetic_Field_Decli...
Oh, and you can't use any external power source.
If probably didn't take that much more magnetic north change to prompt the need to relabel the runways.
Alternately you could move the runway a bit
http://en.wikipedia.org/wiki/File:Earth_Magnetic_Field_Decli...
Still though, even in that animation, Tampa seems pretty stable over time.
Two conversations: #1 "Which runway should I land on?" "Runway Charlie." "Which one is that?" "The one on heading 180 deg."
#2 "Which runway should I land on?" "Runway 18."
I find it interesting that they don't use true north though.