Reciprocal Runway Numbering

Runways are numbered according the magnetic compass direction they are oriented to. They consist of two numbers, one at each end of the runway, each being the reciprocal of the other on the magnetic compass (180° opposite from each other). One number is formed by rounding the compass bearing of one end of the runway up or down to the nearest 10° and dropping the last digit; if this results in a single digit, add a zero to the left of it. The other number is the reciprocal of the first number (see the table of Reciprocal Runway Numbers below). For example, if a runway is aligned north-south, then it is 18/36, not 00/18. The lower number is always listed first. If the compass heading of a runway is 122° you would round it down to 120 and drop the last digit, leaving you with 12. Thus it is called Runway 12/30. If the compass heading of a runway is 37°, you would round it up to 40 and drop the last digit, leaving you with 4. Since this is a single digit, you add a zero to the beginning, giving you 04. Thus it is called Runway 04/22. Both Ellington and Hobby airports have a 04/22 runway.