Peter R. wrote:

Andrew Sarangan wrote:


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.


Certification is most certainly relevant to your query, as that is most
likely what kept that feature out of the TSO C129a certified IFR GPS's.

True, and that capability is permitted by the 146 spec. It does require
WAAS.

This is from the Garmin 500W handbook:

LNAV/VNAV and LNAV Approaches with Advisory
Vertical Guidance

GPS approaches with vertical guidance may be either LNAV/VNAV or LNAV
approaches with advisory vertical guidance. LNAV-only approaches with
advisory
vertical guidance only have LNAV minima listed on the bottom of the
approach plate. The glidepath is typically denoted by a light dashed
line on the vertical profile (Jeppesen only) with an associated
glidepath angle (usually in the 3.00° range). These approaches are
indicated with “LNAV+V”.

For approaches with LNAV/VNAV minimums, those will be controlling. For
LNAV approaches with advisory vertical guidance, the LNAV minimums will
be controlling. Approaches confirmed as “LNAV/VNAV” approaches in the
Jeppesen NavData are indicated

with an “L/VNAV” annunciation. At the time of this publication, not all
of the LNAV/VNAV approaches have been identified as such in the Jeppesen
NavData, therefore some LNAV/VNAV approaches may still be identified
with “LNAV+V” annunciation.