The FAA also publishes new aeronautical charts for pilots every 56 days, and with the next one due on Thursday, it made sense to make the changes at Tampa International Airport effective the same day, she said.

“The Earth’s magnetic fields are constantly changing,” she said. “It’s a very dynamic system so we make these changes effective every 56 days.”

via Shift of Earth’s magnetic North Pole affects Florida airport – This Just In – CNN.com Blogs.