On Mar 4, 9:52*pm, (Alan) wrote:
In article Bruce Hoult writes:

On Mar 5, 8:44=A0am, John Smith wrote:
If you ever want to climb above 15,000 ft in an airspace where a
tansponder is mandatory (which I do regularly), then you are just plain
illegal with the TT21. This may be "fairly meaningless" for you, it's
not for me and should not be for any pilot.

Saying something is "illegal" is a fairly useless statement. A lot of
things are illegal, ranging from driving at 60 in a 55 zone and on up.

I think you need to explain:

- what is the likely safety implication of flying above 15000 with a
TT21?

I suspect the answer is "none whatsoever".

* Unless, of course, the encoder actually cannot encode significantly above
that altitude.

* Or, if it encodes incorrect values, resulting in that airliner hitting you
and going down with all aboard. *That will look about as bad as not having
had a transponder in the first place.

- what is the penalty for being caught doing so? What is the chance of
being caught?

* The first part probably depends on how you are caught.

* * * * Alan

Nice fear theories but there is no reality here. The encoders in the
Trig transponders are not an issue. The TT21 and TT22 use the same
control head and that is where the encoder is.

Current Mode C/gray code (100' resolution) external encoders operate
to a minimum of 30k feet. More expensive expensive encoders get you to
higher altitudes. And to get into a Mode S/serial encoder (25'
resolution) style encoder typically gets you higher than 30k feet as
standard but most of the Mode S transponders we care about in gliders
come with built in encoders.

For all USA gliders after transponder installation a static system
check (Part 43 Appendix E) is required to ensure both altimeter and
encoder accuracy. Nothing in that static systems tests is specific to
type 1 or 2 transponders--just ask the person doing the test if they
can check to 18,000' or higher just to be sure. (and if a Trig encoder
needs adjusting to meet altimeter accuracy the test operator has to
drive it up to 20,000' anyhow to use the calibration adjustment).

What is important is to get people installing and properly using
transponders where we have high density airline and fast jet traffic.
Not only did Trig (and maybe some other products in Europe who are not
available in the USA) significantly lower the cost and power
requirements of installing Mode S but they also significantly reduced
the cost difference between the Class 2 and Class 1 versions of their
transponders. Other vendors had been using that class 1 vs class 2
requirement to create high artificial price differences between their
transponders (for what were basically the same electronics). Trig's
price difference seems only around $200, so pretty marginal, so there
is less reason to use the Class 2 TT21 if class 1 requirement worries
you. The TT22 will use slightly more power than the TT21. Almost all
glider installations of Trig transponders I am aware of are TT21 and
seem to be doing very well.

Darryl