Source of altitude shown on inflight map?
(I guess this is as good a forum as any for this question)
Most of the inflight map systems show altitude as an exact thousand, to a degree of precision which I'm sure does not reflect reality. However today I flew LHR-NRT with Virgin and the altitude was all over the place, not just a few feet off but often showing several hundred different from a proper flight level - way off what I would personally consider acceptable when I'm the one flying the plane. (Even my relatively cheap GA autopilot can keep altitude to within 20' or so in smooth air).
So I was wondering where they get this data from? I find it hard to believe either:
a) AA, UA, BA etc can really fly to an accuracy of 0.5'
b) VS can't fly to an accuracy of 500'
Any illumination welcome...
n5296s