10 degrees: Magnetic variation alters MSO runway orientation

Final approach into Missoula International Airport has shifted over the years due to a magnetic variation that will require changing the runway numbers, airfield signage and checks by the FAA. (Martin Kidston/Missoula Current)

By Martin Kidston/Missoula Current

It didn’t happen overnight, but somewhere along the way the magnetic alignment at Missoula International Airport shifted more than 5 degrees.

And that will cost the airport a lot of paperwork and roughly $60,000 to address.

“In my career, I’ve never had to go through this before,” said Airport Director Cris Jensen. “It’s kind of a complicated thing because it will change our approach procedures.”

Jensen said the runway numbers are assigned based upon compass settings. If one were to stand on the runway and align his or her compass, it would read 110 degrees at one end and 290 degrees at the other end.

That resulted in the original runway designations 11-29 and 7-25. They will soon be changed to 12-30 and 8-26, marking a change of roughly 10 degrees.

“Slowly over time, the magnetic pole shifted a little bit, so it will actually be 120 and 300 degrees,” said Jensen. “We’ll be removing the old markers and putting the new ones on the runway.”

While that sounds easy, Jensen said it’s a bit more complicated, as it changes the airport’s approach procedures. And that requires coordination with the Federal Aviation Administration.

Jensen said the FAA will have to flight check the new designation and approach procedures using an instrument landing system.

“There’s a lot that goes into not just erasing the markings and putting new ones down, but making sure all those other things are thought about and checked,” he said. “It’s a fairly involved process.”

The magnetic variation will require remarking of the runway designators, the placement of new airfield sign panels at every hold bar, and new runway direction signs.

The airport has contracted Morrison-Maierle to complete the work and conduct runway pavement maintenance in the process.

Contact reporter Martin Kidston at info@missoulacurrent.com