Originally Posted by
DaveReidUK
Runways tend not to move overnight.
It would be a fairly trivial task to crunch one of the FMS data providers' runway databases and determine which ones are aligned at exactly 270° (plus or minus whatever the tolerance is).
True, but the magnetic heading can effectively change overnight. It's a weird side effect of the magnetic poles not staying put.
Edit: Came across the following website because a certain drone suddenly was unable to fly when the magnetic database changed on Jan1.
https://www.ngdc.noaa.gov/geomag/WMM/ I don't know the particular correlation to the avionics side of this but looking at the loops and whorls of the magnetic field leaves me dizzy. They track not only the current offsets but the rate at which the offsets change; apparently 9 dimensions all together.