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

Have you considered the effect of flight levels and atmospheric pressure on the display?

If you expect Flight Levels to be to an exact multiple of thousands of feet then you're in for a big surprise over Russia. They use flights levels in multiples of 300 metres and everybody flies to whichever multiple of 100ft is closest to it. Hence flying around at 36400ft is perfectly normal.

On a related topic what is the position with Latvia, Estonia etc which such flights cross. Is it only Russia which has retained the old Soviet levels or do all the old Soviet satellite countries now part of the EU still continue with it ?

Thank you.

WHBM

Most of the former CIS states have converted to feet (Lativa for example). Last time I flew to Kiev (Ukraine) they used feet down to about FL040 then metres for the final approach. I suspect that in a couple of years or so they could well be totally converted.

Having said that, and despite being brought in using imperial units, it is a bit anachronistic is the 21st century with us using a mixture of knots for windspeed, metres for visibility, feet for altitude, and millibars [hectopascals] for pressure.

In this I exclude the US of A, who if nothing else are at least consistent [in being behind the times]!

Russia and China use metres instead of feet. So the altitude will not be in exact multiples of 1000ft. It will be in multiples of 100ft.