John Wayne Airport in Orange County is renumbering its runways because “a normal shift in Earth’s magnetic north has thrown the airport’s runway designations, first assigned in 1965, out of whack,” according to a fascinating story in the Orange County Register.
Reporter Mary Ann Milbourn does a great job of explaining the issue.
Runways are numbered from 01 to 36, representing every 10 degrees in change from 1 to 360 degrees on a compass. When John Wayne’s runways were built in 1965, the commercial runway was designated 19R/1L and the general aviation runway was 1R/19L. The 19 represents 190 degrees south on the compass and the 1 represents the opposite direction, 10 degrees north.
But apparently — and I learn something new every day on this beat — these runway designations might change every so often. Milbourn writes:
The magnetic north rotates about 1 degree every 12 years, or 5 degrees over 60 years. In John Wayne’s case, that means the runway orientation that was 190 degrees in 1965 is now closer to 200 degrees and the one that is 10 degrees is now more like 20 degrees. So the runways will be redesignated 20R/2L and 2R/20L next year.
Ian Gregor, the FAA’s spokesman, told the Register that the agency tells airports they should renumber their runways when the magnetic heading assigned to the airport is off by more than five degrees.