Bill Daniels wrote:
Is it legal/possible/reasonable to install just Mode A transponder (No
altitude reporting)?

Whenever I hear "Traffic 12 O-clock 3 miles, altitude unknown" I look
EVERYWHERE. ahead. Might this provoke more visual scanning by aircraft
crews which could spot gliders without transponders in the same gaggle? A
case of one protecting all?

As a side benefit this would avoid the 24 months Mode C altimeter/encoder
check.

Bill Daniels

Sure, anything is possible/ and/or reasonable. As far as legal goes,
remember if you have an instrument of any kind installed, you are
required by regulation to have it signed off by an A/P in your aircraft
log book. Additionally some reference to weight and bal. should also
be noted even if it's only to say, "no significant weight change." If
you put a transponder in your glider - either with or without an
encoder - it needs to be calibrated and so noted in your aircraft log
book. You are then required to have checked every twenty-four months.
If you are going to put a transponder in the glider, then spring for an
encoder - In for a penny, in for a pound and all that. Without the
encoder ATC as well as TCAS only gets azimuth and range. With the
encoder you get the third demension, altitude.
Sure beats ending up in Denver as a pitot cover on a B-767!

Billy Hill, Zulu