Navaid Theory

[Chris Trott]

Nigel, you are correct that WAAS is only available in North America (Canada and Mexico are partners in the development) at the moment. You'll know it as "SBAS" in Europe as that's what they're developing it as. The actual system is non-proprietary, but I think as with many other things, the reason for separate deployment and separate systems is more due to varying specifications for varying areas (i.e. what works in the US doesn't necessarily work in Europe, especially when it comes to radio frequencies).

Here's Garmin's take on the system - http://www8.garmin.com/aboutGPS/waas.html
And Wiki - http://en.wikipedia.org/wiki/Wide_Area_ ... ion_System

[emfrat]

Skip, Chris, Nigel -
I have before me a UK AIP chart for Coll (EGEL) aerodrome, dated 12 Jun 08. In the top left corner it says:
"GUND(Geoid Undulation) = The height of the Geoid (MSL) above the Reference Elipsoid (WGS 84) at the stated position." (Yes, they really only used one 'l' in 'ellipsoid')
In the data box for Rwy20, as well as the usual Lat/Long it has "Thr Elev 20" and "GUND Elevation 185".
So it would seem there is a number to be used to compensate for the uneven shape of the Earth.

Of course if you stay with FS9, the Earth is flat and you don't need to worry about this new-fangled round concept ;-)

Cheers
MikeW

[Nigel H-J]

Thanks Chris, so if I'm ever lucky enough to get over there, I will have to bring my Garmin with me!!

Regards
Nigel.