On Fri, 18 Feb 2005 21:44:36 -0500, "Eclipsme" wrote:

Well, what I was missing was an understanding of what VPL is. Still not
sure, but at least have an inkling.

Oh. I see your confusion, now. You may think of VPL as indicating the
range of your WAAS enabled GPS altitude indications relative to the true
altitude. So the larger the VPL, the larger the potential error.

The TSO146 certified boxes calculate VPL and, if it is outside some
acceptable range, will limit the type of GPS approaches it will allow you
to conduct.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)