Is it true runway numbers are based off of headings?

So I was watching a Swiss001 video (worst flight simulator) and while playing one of them the runway numbers happened to be 40. To which he said wasn’t possible since the compass doesn’t have 40°on it.

So how does FAA decide on numbers for runways? is it based off of the compass?

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Yup based on the heading/direction the runway is facing.

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Mostly, yes.
Heading’s 1-36 are easy, but after that you drop the last number (for example, heading 40 = Runway 4).

If you have multiple parallel runways, they can be labels L, C, and R. If there are more then three, they might call runway 4 runway 5, even if it’s at heading 40, to prevent confusion.

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And sometimes, they can change the numbers around, like at KLAX with 24L and R and 25L and R parallel.

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This compass rule even causes some airport’s runways (especially close to the poles) to change numbering every now and then due to the magnetic poles moving.

CGP Grey did an excellent and amusing YouTube video about runway headings last year:

The Simple Secret of Runway Digits

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I think you mean 400° as that would be runway 40, which doesn’t exist. But 40° is under 360°, so that would be runway 04.

This doesn’t make sense. Are you saying a heading of 015° would be runway 15? That’s not correct.

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Yes. The runway number is generally the magnetic heading of the runway rounded to the nearest 10, and dropping the trailing zero. The only numbers available are from 1 to 36.

194° = Runway 19
023° = Runway 02
001° = Runway 36 (because 000 → 360)

This StackExchange post has some good additional information about how runway numbers change. I’m sure there’s an esoteric document out there explaining exactly how the FAA decide these numbers in the first place, but I don’t think it’s worth looking up here.

TL;DR: Yes.

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Oh? I didn’t know.

You can check this out in Infinite Flight, spawn at any runway and compare the compass heading to the runway number.

It might not be a perfect match, but it should be close enough for pilots and controllers to get some situational awareness.

What’s the largest difference you can find?

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