
Tampa Airport: Moving magnetic poles forces runway changes - iwwr
http://blog.seattlepi.com/aerospace/archives/234696.asp
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cosmicray
What isn't mentioned in all this, is that the runways were slightly east of
true north in the first place. Please see the FAA diagram on wikipedia...
<http://upload.wikimedia.org/wikipedia/en/8/8e/KTPA-FAA.pdf>

If probably didn't take that much more magnetic north change to prompt the
need to relabel the runways.

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ijuhygtfhyuj
The runways are labelled rounded to the next 10deg so if a runway is 154.9 and
the magnetic pole moves 0.2 deg you go from runway 15L to runway 16L

Alternately you could move the runway a bit

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russell_h
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.

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macrael
The rate of change of magnetic north varies wildly around the world, not based
on latitude. See this fabulous .gif on Wikipedia

[http://en.wikipedia.org/wiki/File:Earth_Magnetic_Field_Decli...](http://en.wikipedia.org/wiki/File:Earth_Magnetic_Field_Declination_from_1590_to_1990.gif)

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gregable
That's fascinating - I always thought it was based on latitude - basically the
difference in angle between the north pole and the magnetic north pole.

Still though, even in that animation, Tampa seems pretty stable over time.

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timrobinson
Couldn't they label the runways relative to geographic north rather than
magnetic north?

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yellowbkpk
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?

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DanielBMarkham
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)

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jcl
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.

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pdx
I suspect it would have been freezing point that was most important, and
whiskey was a readily available source of low freezing point liquid.

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bambax
The lesson here is to use names that don't carry content/meaning. A name is a
pointer.

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lutorm
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.

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InclinedPlane
Exactly.

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."

