Any opinions on the Garmin GNS 480 ! ! !

"Mike Adams" wrote in message =
news:HxXBd.6305$232.4499@fed1read05...
"John R. Copeland" wrote:
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As I've posted earlier, the glide-slope needle in my Flight Director
is not driven from the CNX80/GNS480 unless VNAV minima are published.
This defeats autopilot coupling to the computed glideslope on
non-precision approaches. However, the HSI display of the NAV page
shows vertical guidance for most LNAV approaches, as a welcome aid =
for
stabilized descents.=20
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I just took delivery on my GNS480 upgrade, and in the initial test =
flight, did not see what you are=20
experiencing. We flew the GPS23 approach into P08 (Coolidge, AZ), and =
the GPS07R into KDVT=20
(Phoenix, Deer Valley), and VNAV guidance was provided on the external =
HSI in both cases. Interestingly,=20
these are traditional GPS approaches, not the newer ones with specific =
LPV or LNAV/VNAV minimums,=20
and VNAV was provided in both cases. In the Coolidge case, we took it =
all the way down, and it split the=20
runway laterally and the G/S pointer took the altitude right to the =
threshold. All this out in the middle of the=20
desert with no ground navaids. Very cool.=20
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So, I'm confused by what's causing your restrictions. Could it be =
something specific to your F/D-A/P=20
setup? I don't have either one, so maybe the logic is restricted only =
if there's an autopilot. Or perhaps=20
WAAS updating was unavailable when you tried it. Is it restricted even =
when WAAS is known to be=20
working?
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Mike

That's intensely interesting, Mike. I haven't had WAAS unavailable.
But if it were unavailable, the CNX80 wouldn't show its computed
glideslope presentation on its internal NAV display, either.
Feedback I got from the Apollo tech rep through my avionics shop
said that it was an intentional restriction on driving the VDI needle,
intended to foil 3-axis autopilots from locking onto the vertical
guidance unless VNAV minima were published as part of the approach.

I don't know if the CNX80/GNS480 can be "aware" of whether the
airplane is equipped for 3-axis coupled approaches. Perhaps.
Since I had one of the very first upgrades to CNX80 version 2,
now I'll need to check to see if that VDI restriction was later =
relieved.
Indeed, I originally expected to see the VDI active in my flight =
director,
and that's why I questioned its behavior after my first test flight.
Thanks for those details, Mike.
If you hear anything more about this, please post.

Regarding "splitting the runway", I have an MX20 MFD also,
and it almost always depicts me closer to the centerline of a
runway than to either edge. It's amazing!