# Pilot /Runway Question **URL:** \ **Category:** Factual Questions\ **Created:** [October 17, 2009, 1:20pm UTC](https://boards.straightdope.com/t/pilot-runway-question/514137 "2009-10-17T13:20:34Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Stan\_Shmenge](https://avatars.discourse-cdn.com/v4/letter/s/94ad74/32.png) [@Stan\_Shmenge](https://boards.straightdope.com/u/Stan_Shmenge)\ **Post date:** [October 18, 2009, 5:38pm UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/21 "2009-10-18T17:38:58Z")
Oops, answered in post 14. :smack: ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [October 18, 2009, 5:51pm UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/22 "2009-10-18T17:51:19Z")
> [@Stan\_Shmenge](#): > > Magnetic? Are you sure? It was my impression that the earth’s magnetic field changes over time, and that new magnetic declination maps had to be issued from time to time to compensate for these changes. Do they repaint the runway numbers when this happens? Post #14: > [@Magiver](#): > > As natural magnetic variations change over time then runways will be renumbered. This happened a couple of years ago at an airport near me and it caught me off guard. ---
**Author:** ![pinkyvee](https://avatars.discourse-cdn.com/v4/letter/p/6de8d8/32.png) [@pinkyvee](https://boards.straightdope.com/u/pinkyvee)\ **Post date:** [October 18, 2009, 6:36pm UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/23 "2009-10-18T18:36:20Z")
> [@Mach Tuck](#): > > It’s mostly been covered, but I’ll add a bit about traffic patterns. > > It’s pretty easy to identify the runway you want, but it takes a bit more thought when there are crossing runways, and if you need to make a non-standard pattern entry. > > Most of the time you want to fly parallel to the runway in the opposite direction of the intended landing. This is called the downwind leg, and it’s usually flown so that you make a left turn toward the runway. Easy enough. > > But sometimes you need to enter the pattern at a different point. Controllers at towered airports may ask you to fly at a right angle to the runway, then turn in (entering on a the base leg). To complicate matters, they may require right-hand traffic instead of the usual left. And if there are crossing runways, it takes some good situational awareness to sort out how to enter and fly the pattern. > > As an instructor, I see a lot of new pilots (and sometimes experienced ones) get confused in this situation. If you’re keeping your head in the game it’s not that difficult, but it can take a few moments to think it through. I sent you a PM. ---
**Author:** ![Razncain](https://avatars.discourse-cdn.com/v4/letter/r/9d8465/32.png) [@Razncain](https://boards.straightdope.com/u/Razncain)\ **Post date:** [October 19, 2009, 1:44am UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/24 "2009-10-19T01:44:51Z")
> [@Stan\_Shmenge](#): > > Magnetic? Are you sure? It was my impression that the earth’s magnetic field changes over time, and that new magnetic declination maps had to be issued from time to time to compensate for these changes. Do they repaint the runway numbers when this happens? It wouldn’t be anything to worry about in our lifetime. It takes something like a century for the magnetic compass to move something like 2 degrees IIRC. Since the runways are numbered to magnetic north, rounded to the nearest ten degrees, that’s not going to matter. I do know of at least one exception to the nearest ten degree rule. And that is the D/FW airport. They have five runways all pointing in the same direction. They name 3 of them runways 17-35 left, center and right, while the other two are marked 18-36 left and right to avoid confusion. There may be other bigger airports that have to do this as well. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [October 19, 2009, 1:53am UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/25 "2009-10-19T01:53:17Z")
Re: Magnetic headings. It makes sense to lay runways out along magnetic headings, since the basic navigational instrument in an aircraft is a magnetic compass. ---
**Author:** ![suranyi](https://avatars.discourse-cdn.com/v4/letter/s/e36b37/32.png) [@suranyi](https://boards.straightdope.com/u/suranyi)\ **Post date:** [October 19, 2009, 4:12am UTC](https://boards.straightdope.com/t/pilot-runway-question/514137/26 "2009-10-19T04:12:40Z")
> [@razncain](#): > > It wouldn’t be anything to worry about in our lifetime. It takes something like a century for the magnetic compass to move something like 2 degrees IIRC. Since the runways are numbered to magnetic north, rounded to the nearest ten degrees, that’s not going to matter. > > I do know of at least one exception to the nearest ten degree rule. And that is the D/FW airport. They have five runways all pointing in the same direction. They name 3 of them runways 17-35 left, center and right, while the other two are marked 18-36 left and right to avoid confusion. There may be other bigger airports that have to do this as well. There are several, typically when there are four or more runways all parallel. LAX (Los Angeles International) is another example. With two parallel runways they can call one “Left” and the other “Right”. With three parallel they call the third one “Center”. But with four or more they shift one set by one digit. [Previous page](https://boards.straightdope.com/t/pilot-runway-question/514137.md?page=1)