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They are but the rate is variableChris558 wrote:It also helps when you're in on the downwind leg, i.e to fly the reciprocal heading.
But why does this only affect some Airports? If the poles or Earth position is shifting slightly, surely ALL Airports would be affected.
Tis true, all Admiralty charts have a note of the magnetic variation for the area covered (difference between true and magnetic north) and the rate at which it is changing, usually something like 'Variation 5 deg W in 1997, 0.05 deg E annually'. If you look at a map of magnetic variation it's all over the place, literally, which explains the variable change in variation over the Earth.They are but the rate is variable
Only to me, I still remember them as 28/10 because I moved away from the area before they changed. So rarely hear 27/09 mentioned on the airband, and then wonder where I amHeathrow used to be 28/10
Don't remember it causeing too much trouble .........
The shift takes place when the magnetic heading is close to the midpoint between decimals of dgegrees. Thus EGCC was 236 degrees mag, and a 2 degree shift in variation ( west in this case) would reduce this to 234, thus making the mag heading nearer 230 than 240 - hence the change here. If, however, its heading had been 239, no change would have resulted, since 237 would still be nearer 240 than 230Chris558 wrote: But why does this only affect some Airports? If the poles or Earth position is shifting slightly, surely ALL Airports would be affected.
The annual change is very little in the UK...only a fraction of a degree...so several years for 1 degree and many years before a change of runway nomenclature is required...Heathrow was 28/10 for my whole BEA/BA career and it changed to 27/09 just after I retired...Have now been retired for 21 years.....cstorey wrote:The shift takes place when the magnetic heading is close to the midpoint between decimals of dgegrees. Thus EGCC was 236 degrees mag, and a 2 degree shift in variation ( west in this case) would reduce this to 234, thus making the mag heading nearer 230 than 240 - hence the change here. If, however, its heading had been 239, no change would have resulted, since 237 would still be nearer 240 than 230Chris558 wrote: But why does this only affect some Airports? If the poles or Earth position is shifting slightly, surely ALL Airports would be affected.
Peter, like you I recall the variation in the UK being pretty static at about 7W for the best part of 2 decades, but interestingly, this very afternoon I was looking at a Prestwick let down plate from 1954 which showed the Varn as 13W, so I assume there was some sudden shift in the late 1950s/early1960spetermcleland wrote:annual change is very little in the UK...only a fraction of a degree...so several years for 1 degree and many years before a change of runway nomenclature is required...Heathrow was 28/10 for my whole BEA/BA career and it changed to 27/09 just after I retired...Have now been retired for 21 years.....
