Airports are constantly renaming their runways—and not because of changing styles or new regulations. The surprising reason is that the magnetic fields of the Earth will not stop shifting. This may seem like no big deal, but it costs hundreds of thousands of dollars to continually replace airport signs and repaint runways.
So why does this happen? As Wired explains, the magnetic North Pole can move by as much as 40 miles a year. This wild variability is a problem for pilots and airports, which name their runways by how may degrees off north they are.
For example, Wichita's 14/32 runway, which can be used from either direction, is either 140 degrees clockwise from north (or 320 degrees, if you're using it in the other direction). These numbers are rounded to the nearest ten and shortened to two digits. This is an easy way for pilots to make sure they're landing and taking off from the right strip.
Our planet's tricky magnetic fields complicate this easy system. The FAA orders airports to change runway names once they've changed so much that they'll no longer round to the same number. So, for example, a runway called 36 wouldn't change if the degrees off north went from 355 to 359. But if it went down to 354, it'd need to be rounded down to 35, and the name would be changed.
This renaming process is currently happening at the Wichita Eisenhower International Airport. Runways 1L/19R, 1R/19L (these refer to parallel runways, the R and L stand for "left" and "right") and 14/32 will be changed to 2L/20R, 2R/20L, and 15/33. This is the first time the runways will be renamed since 1954.
Most of the time, these distinctions don't matter much. Airplane pilots can visually identify the correct runway even if the number is a few degrees off. But mislabeling can occasionally have dire consequences, such as the 2006 Comair Flight 5191 crash in Lexington, Kentucky, which killed 49 people. An investigation from the National Transportation Safety Board determined that the crew didn't identify the correct runway, and thus tried to take off from a runway that was too short. Keeping up with our pesky magnetic fields may be a bit of a pain, but it's worth it to keep flying as safe as possible.
