OAK navigation chart
Part of the flight navigation map of the central Bay Area. Some aspects of working in this complex airspace are surprisingly simple. Image from SkyVector.com

The Metropolitan Oakland International Airport has a distinguished record in the annals of flight, from Amelia Earhart to the pioneering exploits of Lester Maitland and Albert Hegenberger, all of whom have Oakland streets named for them. Starting in the late 1920s, pilots at OAK launched and landed their planes on Runway 27, now part of the airport’s North Field. Passenger jets landed on mighty Runway 29, almost two miles long. But this October, that changed. Runway 27 was forced by the authorities to become Runway 28, Runway 29 became Runway 30, and a long tradition was ruptured—or was it?

Airport runway numbers are not arbitrary, like street names. They actually designate the runway’s direction. The system is simple: take your magnetic compass direction (in degrees from zero to 360), round off to the nearest 10 and drop the zero. Pilots can see the runway’s designation right on their own aircraft compasses.

Magnetic navigation is the most conservative, failproof method there is because the magnetic field is generated by the planet itself. When satellites fail, the ground is shrouded in fog or snow, windshields are smeared, the stars and moon are obscured and worse, the compass is constant…sort of.

The Earth’s magnetic field arises from its own substance as the huge body of molten iron in its core stirs with the Earth’s rotation and the moon’s steadying hand. Electrical currents in the iron generate magnetic fields that struggle against the stirring, acting like a natural turbine and powering the magnetism that draws our compass needles to attention. This sounds busy, and it is. The geomagnetic poles, north and south, are always wandering and must be closely monitored by a network of observatories to keep navigation accurate. That’s how the authorities knew when to change Runways 27 and 29 to 28 and 30.

The difference between magnetic north and true north is important to serious off-road travelers: hikers, wilderness explorers, sailors and airline pilots. The early aeronauts were exceptionally dependent on their compasses, like Earhart and the other heroes of the Oakland airfield. Imagine lifting off from Oakland, turning left and heading out over the open Pacific at a hundred miles an hour to fly to Hawaii, all by yourself. I don’t know about you, but it makes me shiver. But as they flew, the magnetic field kept them steadily on course, even though the field itself is unsteady in the longer term.

Maitland plaque
This plaque is in front of the Business Jet Center on Earhart Road, next to Runway 27—I mean, 28. Andrew Alden photo

Now put yourself in the mindset of geologic time: a thousand years is like a moment, a million years like a minute. At that speed, the magnetic poles and their motions turn into a flicker, a blur, a cloud of activity centered at the true north pole. The magnetic field is steady again.

Geologists use the iron-bearing minerals of rocks to determine the magnetic poles of the deep past. They take a lot of samples and average out the measurements, arriving at a paleo-magnetic pole. That might seem like a lot of work, and it is, but it has taught us an amazing thing. Young rocks—just a few million years old, you understand—point to a paleopole that’s the same as today’s. But in older rocks, as we go back in time the paleopole steadily veers away from north. The very continents themselves are moving around, as surely as airliners. Once this fact was accepted, in the 1950s, we were moved inexorably to the modern theory of plate tectonics, and geologists had one more thing to give them that faraway look.

Changes in Earth’s Magnetic Field Lead to Renamed Oakland Airport Runways 26 December,2013Andrew Alden

  • Dan Brekke

    OK … so the OAK runway designations have changed. Has the apparent magnetic shift necessitated a reconsideration of designations for the runways at SFO, just a few miles to the west? Are any of the other local airports having to change?

    • Andrew Alden

      Dan, apparently the runways at other local airports haven’t crossed the line yet.

  • KoKotheTalkingApe

    So magnetic north moved at least a few degrees since the Oakland Airport was built? That seems very fast. Also, what do they name two parallel runways? And if a runway runs exactly north-south for example, is it named “0” for zero degrees, or “18” for 180 degrees? Is an east-west one named “9” or “18”? And even very simple hand compasses can be adjusted for declension (the difference between true north and magnetic north), at least for a given area. Couldn’t the electronic compasses on airplanes do the same thing, and wouldn’t that be easier than renaming the runways?

    • Andrew Alden

      Koko, Runway 30 is called Runway 12 if you’re flying toward it from
      the north. And the twin runways at North Field are named 28L and 28R,
      for left and right, as you approach from the south, and 10L and 10R if
      you’re flying in from the north. It’s extremely simple, requiring no
      thought on the pilot’s part.

      You don’t want to do anything to a compass; that would make it
      dependent on something other than the magnetic field. The local
      declination is what is so carefully monitored by magnetic observatories.

      • KoKotheTalkingApe

        Thanks for the info! It still seems strange that magnetic north would move so much. And now that I think about it more, the airports I have seen have runways pointed in only a few directions, not in all directions like the spokes of a bicycle wheel. Why would they bother changing Runway 29 to Runway 30, like the article says? The other runways would be something like 3 or 21. Not much chance of confusion there. And I just checked the plans for DIA. They have four north/south runways, named 35/16 L and R, and 34/16 L and R. Why is one 35 and the other 34? They run in exactly the same direction.


        • Andrew Alden

          How interesting! I do notice that the two pairs of runways are 0.1 degree different. There must be some convention to cover this circumstance.

          • KoKotheTalkingApe

            Yes, I see that now. I’d imagine a 0.1 degree difference in heading would be difficult to see with a magnetic compass. Why wouldn’t they say 16/34 West L and R, and 16/34 East L and R? Calling one pair 15/35 as they do (I got the names wrong originally) implies they are ten degrees different, not one-tenth of a degree different. Misleading.

        • tcasey

          The number of runways, or how many directions they have are based on the wind. What is the best wind direction for the easiest landing. And the more traffic an airport has will determine how many and in what direction will be used the most.

          • KoKotheTalkingApe

            Thanks, but I think you may have misunderstood me. I was saying that since airports have only a few runways, there is not much need to specify the compass headings of the runways with that scheme the author of this article describes. You could do just as well, most of the time, just to say South L or South R, or NW L or R. For the compass heading to be useful, you would already have to see the airport.

  • Tony Godkin

    Great questions, KoKotheTalkingApe ! Parallel runways are named 28L and 28R. E-W runway would be 9-27. The degree change was fractional.

    • KoKotheTalkingApe

      Thank you!

  • MikeG

    Magnetic North rotates about 1 degree every 12 years or roughly 5 degrees over 60 years. The FAA recommends a change of runway designation with any declination of 5 degrees or more. So in reality there is nothing unusual about the timing of this change and it is not regional magnetic shift as some have implied but effects airports worldwide except for those in NDA-Canada which are numbered by true north rather than magnetic north. I understand Geologists normal scale of time in dealing with anything but am disappointed in the assumptions made by the author here when simple fact checking that should be a part of any article would have revealed the simple facts.

    • Andrew Alden

      Mike, the geomagnetic field is too complex for rules of thumb. Have a look at this animation covering the last 400 years: http://www.historicalatlas.com/mag/

      • MikeG

        Andrew rather than base your scientific view on a single gif animation perhaps you would be interested in seeing the actual Declination Data for Oakland or many other US points where you can quiet simply see that my prior mentioned “rule of thumb” that is in use by the FAA and successfully used by Pilots since the inception of the runway system hold rather accurately. Several other area airports have renumbered as well as many airports world wide. http://www.ngdc.noaa.gov/geomag-web/#ushistoric

  • Peter Naus

    Well, if the Sun’s magnetic field can flip every so often (as it’s just about to do), and the Earth’s magnetic field flips roughly every 50kyears, and we’re 20kyears late for a geo-flip, what’s a degree or two for light plane pilots?

    It’s far more of an issue for cattle-carriers!


Andrew Alden

Andrew Alden earned his geology degree at the University of New Hampshire and moved back to the Bay Area to work at the U.S. Geological Survey for six years. He has written on geology for About.com since its founding in 1997. In 2007, he started the Oakland Geology blog, which won recognition as “Best of the East Bay” from the East Bay Express in 2010. In writing about geology in the Bay Area and surroundings, he hopes to share some of the useful and pleasurable insights that geologists give us—not just facts about the deep past, but an attitude that might be called the deep present.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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