In the USA there are simple and fatal flaws with any system that
includes ground based radar and a controller near a high density airport.

First, as already mentioned, the controller's normal display is
processed information. The is often referred to as secondary radar.
Basically it is just the transponder equipped traffic with data tags.

Second, as already mentioned, the system is normally configured to drop
out targets that have a low ground speed or don't have a ground track
that is going somewhere (e.g. circling). So a radar reflector wouldn't
be much help. It isn't the size of the return that gets the target
filtered out under these circumstances.

Third, and probably the greatest problem, if there are too many 12XX
returns (VFR transponder equipped traffic in the USA) the controller can
filter the specific codes or blocks of codes.

The was a mid-air between a commuter flight and a skydiving jump plane
between Denver CO and Cheyenne WY about 15 or 20 years ago. The
commuter flew into the climbing jump plane. Since they we both above
12,500 MSL (about 7,000 AGL), it was assumed the commuter pilots were
heads down in the cockpit. The jump plane was using a transponder code
of 1234 and ATC had 12XX code filtered for the higher altitudes. The
jump plane was not talking to ATC. Oops...

Other than a TCAS installation (aircraft to aircraft), the only way a
transponder will help us is if the ATC facility in the area knows about
the glider operations and can (or will) operate their equipment in a
manner that allows the controller to see the glider traffic. That means
we have to work with the local ATC folks. Otherwise, it is so much extra
ballast and power draw in the glider.

Even when the technology should help, local procedures can negate the
technology. Since the way we operate gliders does not fit in the
general transportation model the ATC system is designed to support,
putting a transponder into a glider without working with the affected
ATC organization does little to help the situation.

Dave Rolley

Mark James Boyd wrote:
BTIZ wrote:

you'd be better off stuffing in a transponder for their TCAS and for ATC to
really see you.


I think we all understand that putting in a transponder and a
big battery is a more complete solution. I think those
on this thread are simply looking at the lower tech, less expensive,
no recurrent certification alternatives.

At $50 and one pound, this looks pretty good. At $1000 and
10 pounds (including the extra battery) + $160/every two years,
I suspect we'd see fewer takers.

I personally also love the idea of the "star" multi-faceted
reflective tape. I despise the green and light grey color of
my current airplane, for example.

Cheap, passive, low cost solutions have a sort of engineering elegance,
don't you think?

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Mark J. Boyd