"Clark" wrote in message
...
A Lieberma wrote in news:58728052-dba6-4fb3-8e25-
:

On Nov 24, 7:38 pm, "BT" wrote:
You do not mention the make and model of the transponder and I did not
se
e
it in the video. The newer garmin (and others) transponders (if tied to
a
GPS) will automatically switch from STBY to ALT when a set ground speed
i
s
reached and return to STBY when it is slowed below that ground speed. It
is
possible to turn off ModeC and just squawk the code. It is very unusual
f
or
the altitude to miss report.

BT,

I don't remember the make and model myself, it was digital in that it
was LCD looking screen rather then LED (green background)

Googling the Garmin transponder product, buttons look the same, just
don't know the model.

Plane had a Garmin 430 but I don't think it was tied into the GPS.

What you describe going from STBY to ALT worked as advertised and that
was a first for me. The display showed FL 4100 which I took to be the
reported mode C as that is what KJAN said. It was 700 foot off the
altimeter reading. Altimeter was spot on when we verified ASOS
altimeter to field elevation.

What got me was I couldn't and didn't know what the standby buttoon
was (or was not) doing since it didn't indicate no mode C, just
continued to show the FL value.

I assume STBY would stop the altitude reads???

STBY should stop all transponder response on the Garmins. Just pressing
"On" rather than "ALT" should give Mode A.

I just put a 327 in my aircraft - thanks for posting this 'cause it gave
me
an excuse to re-read the manual to verify that "On" is Mode A. I'll check
it tomorrow for some visual feedback that Mode A is active vice Mode C.

This is correct. "On" mode kills ModeC, but allows ModeA. It's the same on
most transponders, even those with analog readouts.