5 ms·
Couldn't they label the runways relative to geographic north rather than magnetic north?
by timrobinson 16y ago
Couldn't they label the runways relative to geographic north rather than magnetic north?
- iwwr 16y agoProbably has something to do with magnetic navigation. Are there any aviators who can explain things in more detail?
- maigret 16y agoThe 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.
- yellowbkpk 16y agoImagine 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?
- DanielBMarkham 16y agoAnd 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)
- pavel_lishin 16y ago"We wouldn't be lost if Bob here hadn't drank the compass."
- jcl 16y agoThe 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.
- pdx 16y agoI suspect it would have been freezing point that was most important, and whiskey was a readily available source of low freezing point liquid.
- DanielBMarkham 16y agoI've read that as well. 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/ 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.
- ZoFreX 16y agoI doubt any pilot would forget their grid north / magnetic north conversions. I hope not, anyway. That stuff got drilled into us in the cadets.
- robryan 16y agoIsn'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.
- borism 16y agothat just means there is a market for ultra-low-power battery-assisted magnetic-to-true-north converters!
- maigret 16y agoICAO 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?
- wtallis 16y agoNo. The magnetic declination can be quite significant even in the continental US, and it isn't determined by latitude alone: http://en.wikipedia.org/wiki/File:IGRF_2000_magnetic_declination.gif http://en.wikipedia.org/wiki/File:IGRF_2000_magnetic_declina...
- jberryman 16y agoTrick question: the correct answer is you eject immediately.
- getonit 16y agoThen they wouldn't match a (real) compass.
- lucasjung 16y agoyellowbkpk 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.
- hugh3 16y agoThis is all fine and dandy until the next geomagnetic reversal, at which point we suddenly find everything 180 degrees out of phase.
- AndrewDucker 16y agoThankfully, runways are numbered with _both_ numbers. So 18/36 or 9/27. Total reversal would leave the numbers the same...
- rlpb 16y agoEach number labels one direction/end, so they'd still have to be swapped round.
- yogipatel 16y agoNo, 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. 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_Declination_from_1590_to_1990.gif http://en.wikipedia.org/wiki/File:Earth_Magnetic_Field_Decli...
- yogipatel 16y agoIf you could come up with a system that could always determine where geographic north is. Oh, and you can't use any external power source.