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This question was prompted by this answer to another question by Jamiec.

As the magnetic poles drift (usually pretty unpredictably), runway numbers become inaccurate. As noted in the linked answer, this has resulted at the very least in the renaming of the 15/33 runways at Madrid to 14/32.

How often does this happen, and at what point is it no longer reasonable for pilots to make the corrections necessary to make a smooth landing, requiring a renaming of the runways?

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  • $\begingroup$ Runway renumbering. I've seen charts showing magnetic declination variation in the past, and it's certainly constant! $\endgroup$ – Jules Jan 18 '17 at 19:38
  • $\begingroup$ My experience (in the Florida area) is that magvar shifts enough to require runway number changes every 10 years or so -- it is location dependent. The local magvar has shifted about 2.5 deg over the last 25 years. $\endgroup$ – Gerry Jan 18 '17 at 19:42
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    $\begingroup$ @Jules: That's not constant $\endgroup$ – mins Jan 18 '17 at 19:46
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    $\begingroup$ My previous comment should say every 10 years at one of the local airports. Since the Runway numbers are to the nearest 10 degrees (+/- 5 deg), it depends on the actual runway alignment relative to the transition point. For some airports, it may not happen for another 80 or 90 years. $\endgroup$ – Gerry Jan 18 '17 at 19:51
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    $\begingroup$ In the style of the duplicate; short answer: when its appropriate, medium answer: when it has drifted >3 degrees, long answer: read Lnafziger great answer :) $\endgroup$ – Jamiec Jan 18 '17 at 21:12