NewsOn6.com

TULSA and OKLAHOMA CITY, Oklahoma -- Oklahoma's two largest airports are waiting for word from the Federal Aviation Administration on whether they'll have to change the names of their main runways.

The reason:  changes in the location of Earth's magnetic north pole.

While the geographic north pole never moves, the magnetic north pole is in constant flux.  In fact, a study published by National Geographic in late 2009 found that the pole was moving at 40 miles a year.

That means any structure built along a certain magnetic heading, like a runway, may eventually not match that heading anymore.

Case in point, the main runway at Tampa International Airport in Florida.  For years the busiest runway there has been called 18R/36L.  But that runway is closed until next week so that it can be renamed 19R/1L, as per instructions from the Federal Aviation Administration.

And now, other cities that have north-south runways, like Tulsa and Oklahoma City, are wondering if they'll need to do the same soon.

The names given to runways by the F.A.A. are a shorthand version of the heading a pilot sees when lined up on that runway.

For instance, the two north-south runways at Will Rogers World Airport in Oklahoma City are called 17/35.  A plane landing to the south would fly a heading of 170 degrees, and would land on either 17L or 17R (for left or right), according to instructions from ground controllers.

A plane landing on either of the two exact same runways, but on a northerly course, would be instructed to use either 35L or 35R, because the plane would be on a heading of 350 degrees.

The names are painted on the ends of the runways in huge block numbers and letters.

Alexis Higgins, director of marketing for Tulsa's aviation department, said the F.A.A. has not contacted her department about making a change at T.I.A.  Tulsa's main runways are called 18/36.  Higgins said the last time T.I.A. had to change its runway names was in the late 80s.

Karen Carney, spokesperson for Will Rogers World Airport, said the last time that airport had to change a runway's name was about 25 years ago.  But she said it was the airport's crosswind runway, which became known as 13/31, not the main north-south runways.

Higgins said it's common for airports to have to change their runway names every 20 to 30 years.