Sunday, August 20, 2017

Magnetic shifts prompt a renumbering for runways at McCarran International Airport (KLAS)

The Las Vegas skyline constantly changes, but for decades airline pilots could rely on landing at runways 7L/25R and 7R/25L at McCarran International Airport.

But just like many of the Strip’s classic casinos, the names of the airport’s two longest runways are history.

A wrecking ball or implosion wasn’t needed in this case. The change goes to the Earth’s core.

A geographical shift in the planet’s magnetic poles prompted the Federal Aviation Administration and airport officials to redesignate the runways last Wednesday as 8L/26R and 8R/26L, McCarran spokeswoman Christine Crews said.

It might not seem like a big deal on the surface. But pilots and air traffic controllers rely on navigational aids and flight procedures that are based on magnetic headings, which change over time.

The FAA re-evaluates shifts in the poles every five years and renumbers any runways that have a magnetic shift of more than 3 degrees. The lucky number for Las Vegas was 4 degrees.

It’s believed to be the first runway renumbering for McCarran International Airport, FAA spokesman Ian Gregor said. Airline pilots soon will notice the update in airport directories and charts.

Airports paint markers on the runway that indicate magnetic north and also true north, which don’t line up because “the Earth’s magnetic field is not that simple,” said Jeffrey Love, a research geophysicist for the U.S. Geological Survey.

In fact, renumbering airport runways is pretty common, Love said, because the Earth’s magnetic field changes by approximately one-tenth of a degree annually.

The slow change is caused by fluid motion in the Earth’s core, which is the source of our magnetic field, Love said. As the fluid changes, so does the magnetic field.

“It’s amazing how something that occurs so far and deep in the Earth’s core could have this type of implication on us,” Love said.

Seattle’s King County International Airport also renumbered its runways last week because magnetic variation, according to the FAA. Changes in the magnetic poles also led to runway changes in recent years at Tampa International in Florida and John Wayne International in Orange County, California.

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