Andrew Sarangan wrote:

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.

A handheld Garmin 196 (I think that is the model a pilot-friend had with
him a couple of years ago) that we took up on a practice IFR flight did
just that. It displayed a glideslope for a non-precision approach. If the
cheaper handhelds can do it, then why don't their IFR-certified TSO C129a
big brothers do it? Because it wasn't part of the certification and
therefore, regardless of their ability to provide this feature, are
restricted from doing so due to the certification.




I am sure you are correct, but it doesn't seem to make a whole lot of
sense too keep a useful feature out of certification unless there is
something dangerous about it. I don't see anything unsafe about
providing a glideslope to a nonprecision approach.


The G/S has to be either Baro VNAV or WAAS "electronic" to be certified
for the approach phase of flight, primary or advisory. The VNAV path
provided by a receiver that doesn't have WAAS TSC146 certification would
be very unreliable.