Hi Everyone,A couple of days ago my local International Airport Changed its runway headings from 24R and 24L to 23R and 23L.I've always thought the assignment Number related to compass heading!! Anybody know the technical reason for doing such a thing??RegardsJohn

John,I believe that when variances between the magnetic compass heading and runway alignment are significant enough, then the runway heading is "updated" to match as much as possible the actual heading.The earth's magnetic poles are actually drifting, therefore, the actual headings will change a little each year. Eventually, I'm guessing, the magnetic headings that match your runways drifted closer to 230 degrees than 240. In fact, you'll note that many terminal charts will list a variance.This is all a guess on my part, but I would think the drift would be the reason.

Hi RandallThaks for That....I had no idea it could drift that much (10 degrees) in such a short period of time. The airport has been using Runway 24 from about the 1930's I think.I cant imagine the problems this must create.RegardsJohn

John,The actual original runway headings may have been something like 236. If the variance is now something like 233, it would only take a few degrees to mandate a runway ID change.

John,I work at sea. Our charts show the variation for the areas they cover.At the moment it is decreasing around 4 minutes annually, therefore 15 years would make a whole degree difference.Other areas have vastly different variations and rates of change.We use gyrocompasses, of course but we also have to carry a magnetic compass. It's a legal requirement.Good practise dictates that we also note the magnetic heading and appropriate deviation and variation for each course we steer.Colin

Randall is right if the original heading was say 236 degrees and the new heading is now 235 the runway would be renamed 05-23 instead of 06-24 asit's at "6" I.E. 056,236 ETC that the runway's I.D. would change. So for say a designator of 24 a runway could have a heading from 236 to 245 degrees and still have the same number. Hope this is of some help to you. Dan Martin.

Thanks Dan and Colin,You learn something everyday..........Thats why I like this forum so much, because you guys have such a wide range of knowledge and experience.Thanks for the infoRegardsJohn