"Peter Clark" wrote in message
...
On Fri, 05 Sep 2008 22:50:53 -0400, Bob Noel
wrote:

In article ,
John Smith wrote:

Perhaps I am missing something obvious, but why would you need (or
want)
two
transponders for new aircraft?

Required if you fly above FL180 isn't it?

Do have a FAR reference for that?

91.215(b)(1) requires transponders in class A airspace. What I've
seen is that most pressurized aircraft and turbines in general have
tow installed - does ATC routinely bounce you out of class A with inop
transponders, thus the commonality of 2 in those applications? Can't
seem to find a requirement for dual installations tho.

They can, but probably won't. ATC can still track a target radar only so
long as coverage permits, although there will be no altitude displayed and
must be queried.