The runway numbers at Boeing Field changed Thursday for the first time in 50 years after the Earth’s magnetic poles shifted slightly, King County officials say.

The Federal Aviation Administration-assigned numbers at Seattle’s second-busiest airport (officially called King County International Airport) have changed from 13R/31L for the main runway to 14R/32L, while utility runway 13L/31R is changing to 14L/32R.

Runway numbers are assigned based on compass headings. For example, a plane taking…