On 3/4/2011 9:52 PM, Alan wrote:
In Bruce writes:
On Mar 5, 8:44=A0am, John 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.

We need to be sure we are talking about the same regions (country and
altitude). For the USA, Class A airspace starts at 18,000', so for below
that altitude, there is no effective difference between the two classes
of transponders for pilots operating VFR.

If you intend to operate in USA Class A airspace without waiver, then
getting the higher altitude rated transponder makes sense. The extra
cost of the unit is small compared to the ongoing testing requirements
of your transponder, altimeter, and static system, so there is no point
in taking a chance the encoder might not be accurate enough at the high
end (30,000+?).

I am still curious about the differences between the two models, beyond
the obvious one of output power.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz