On 6 Jan 2007 21:33:52 -0800, "Andrew Sarangan"
wrote:


Peter R. wrote:
Andrew Sarangan wrote:

Something I never understood is why LNAV approaches don't automatically
show a glideslope so that the airplane arrives at the MDA at the VDP.

Perhaps because it wasn't part of the certification at the time?


Perhaps my comment was not clearly stated. When you fly an LNAV
approach (or any nonprecision approach for that matter) instead of the
traditional dive and drive you can mentally calculate the vertical
speed required (VSR) to arrive at the VDP at a constant glide angle .
That mental calculation could be easily performed by the GPS and
displayed as a glideslope. But I have not seen any GPS do that.
Certification is irrelevant. We are not talking about a lower minimum
or anything new that we not already allowed to do.

The CNX80/GNS480 with current SW will do that for many (not all) LNAV
approaches. It is called advisory vertical guidance and available when
published. I believe the presence of a VDP is one factor that usually
triggers this availability.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)