Extreme Magnetic Deviation

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After landing in Chicago, the plane I was on stopped on one of the runways of O’Hare international airport. We sat for about thirty minutes just in front of the signs pictured below. For me, the signs led to more questions than answers. My first few questions are listed below. Please feel free to add more.


  • What do they have under the runway that would cause extreme magnetic deviation?
  • Why would they put something like that near a runway?
  • If extreme magnetic deviation is possible, how is checking the compass again going to help?
  • If Black Sabbath is right, shouldn’t I be worried about turning into Iron Man from being in a magnetic field for so long?


  • So, to get to M7,turn left AND to get to M7, turn right, but right now we’re sitting smack dab on M. Knowing that, is M where we want to be?
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  1. I know, I know! And today is only my first day visiting you! In cold weather climates, it is common that Electric heating elements are imbedded in the runways to keep key areas such as stopping & turning areas clear of any ice. When the devices are in use, the electic current will mess with a compass. You guys were definitely on to something. Now I can’t help you with M7! As they say, if you don’t know where you are going either turn will take you there!

  2. Thanks for the answer UP! It makes sense that they need to keep the runway warm, but I still am curious how checking the compass again will help if it isn’t giving accurate readings in the first place.

  3. Just saw the same sign…did a Google search for terms and found your post. I am pleased curiosity can be shared across space-time.

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