For the first time in nearly a half-century, both runways at John Wayne Airport will receive new number designations Thursday due to a gradual shift of the Earth’s magnetic poles.

The airport’s 5,700-footcommercial jet runway will become 2L-20R while the 2,887-foot general aviation runway will become 2R-20L.

“All of the numbering is to be done by Sept. 18, when the FAA (Federal Aviation Administration) publishes its quarterly updates with new logs for pilots,” airport spokeswoman Jenny Wedge said.

New signs are to replace old ones, electrical wires have been replaced and work crews are ready to strip and repaint stripes and other markings on the runways, she said. The work is scheduled to take place at midnight tonight and be completed six hours later, when flights resume.

“We started planning over a year ago,” Wedge said.

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 the mid-1960s, 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.)

The new runway designations are needed because the magnetic North Pole is not the same as the geographic North Pole.

The magnetic north is the place that a compass points to based on Earth’s magnetic field. Those headings are used to designate runway numbers – essentially their compass address – so that pilots know where they are going.

But the magnetic north rotates about 1 degree every 12 years, or 5 degrees over 60 years, according to a Register report last year. For John Wayne, that means the runway orientation that was 190 degrees in 1965 is now closer to 200 degrees, the Register story said.

Contact the writer: pmaio@ocregister.com or 714-796-7884