"Ron Rosenfeld" wrote in message =
...
On Mon, 25 Oct 2004 18:52:13 GMT, "John R. Copeland"
wrote:
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"Ron Rosenfeld" wrote in message =
...
On Sun, 24 Oct 2004 23:57:17 GMT, "John R. Copeland"
wrote:
=20
However, I have not (yet) found in the pilot's manual any
explanation of when VDI drive is withheld from an external HSI.
By flying several different kinds of approaches, I seem to see
that the external VDI will be active *only* when VNAV minima apply.
Only on precision approaches having DH instead of MDA,
my autopilot could arm and capture the glideslope,
exactly the same as an ILS.
On non-precision approaches my external VDI needle remained
driven out of view, even though its glide-slope flag was pulled,
and as a result I could not arm the glide slope for automatic =
capture.
=20
John,
=20
I won't be upgrading my CNX80 until the end of December, but in =
Newsletter
5 from Garmin there is a description indicating that Glideslope =
guidance
should be available on your HSI for LNAV/VNAV, LPV *and* =
"non-precision
approaches with defined vertical paths" so long as the HPL or VPL =
minimums
for the approach are not exceeded.
=20
Perhaps something has changed since that document was written; or =
perhaps
there's a glitch in your wiring.
=20
--ron

Ron, I no longer have newsletter 5, but I can't fault the newsletter =
announcing=20
availability of the version 2 upgrade, because the new NAV display in =
the
CNX-80 performs as the attachment to that newsletter described.
For LNAV approaches, I have not found where that attachment promised
glide-path guidance on an external indicator, only on the internal NAV =
display.

The undocumented part concerns the drive to the external VDI in my =
flight director.
Wiring can't be faulty, because it works flawlessly on ILS and VNAV =
approaches.
My avionics installer promised today to inquire about that with his =
factory rep.
If I get clarification, I'll share it here.
---JRC---
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Perhaps I misunderstood your original post.
=20
I didn't see anything in either promising external VDI signals for an =
LNAV
approach unless it fell into the category of being a non-precision =
approach
with associated vertical path data. (And which could therefore =
include
other types of non-precision approaches).
=20
There is an extra explanatory paragraph in newsletter 5.
=20
-----------------------
Attachment:
=20
Glideslope guidance for LNAV/VNAV (Gamma 2) and LPV (Gamma 3) =
approaches,
and advisory vertical guidance for other non-precision approaches with
vertical path data associated with them.
=20
-------------------------------------
=20
Newsletter 5:
=20
Glideslope guidance for LNAV/VNAV (Gamma 2) and LPV (Gamma 3) =
approaches,
and advisory vertical guidance for other non-precision approaches with
vertical path data associated with them.=20
=20
We've discussed this feature in the newsletter before and here are =
some
nuts and bolts. All LNAV/VNAV and LPV approaches as well as =
non-precision
approaches with defined vertical paths will have vertical guidance
displayed on your HSI or CDI. This will drive the CDI and VDI and they =
will
behave as they would during an ILS approach.
=20
--------------------------------------
=20
=20
--ron

Thanks, Ron, for excerpting newsletter 5, which I've lost.
Yes, there's been a change since newsletter 5, which seemed to promise
that an external VDI would display vertical guidance on non-precision =
approaches.
For VNAV precision approaches, the external VDI indeed does behave
as it would during an ILS approach, and the autopilot responds the same,
too, going through the modes of GS-ARM and GS-CAPTURE.

Now, though, non-precision LNAV approaches with defined vertical paths =
will
display vertical guidance only on the new NAV display page of the =
CNX-80,
but the external VDI instrument will not display that same vertical =
guidance.
In LNAV, my glideslope flag is retracted, but the glideslope pointer is =
driven
beyond the end of the scale, hiding it from view throughout the =
approach.

In the remaining case of LNAV approaches without defined vertical path,
the VDI portion of the CNX-80's NAV page is entirely absent.

As I mentioned in a follow-up post, later than the one you replied to,
the intentional suppression of drive to external VDIs effectively =
prevents
a 3-axis autopilot from locking onto the vertical guidance information
during a non-precision approach. The pilot must manage the descent.

I do not know whether that choice was at Garmin's volition,
or whether it was an FAA requirement.
---JRC---