The magnetic variation data are stored in the FMC (I think, can't remember for sure). Unfortunately the information is hard wired into the system during construction so is not capable of rapid update like the monthly AIRAC NOTAM data changes, for example. It requires a hardware mod, presumably a new chip, to change from the variation map used at the time of construction to the later one, at a cost of some thousands or even tens of thousands of dollars. Great planning by somebody. There was an article in Boeing's Airliner a few years ago; apparently there are two variation maps, one is about twenty years old (the one in most aircraft), the other is about five years old and is presumably only in aircraft built since then.
Last edited by Hew Jampton; 4th October 2002 at 22:19.