On Dec 8, 12:03*pm, jcarlyle wrote:
For two reasons: *(1) it costs less to perform the biannual
inspection, and (2) you aren't broadcasting your tail number to the
Feds. Of course, you'll only get a 10 year life out of it...

-John

On Dec 8, 2:54 pm, Andy wrote:

Why would anyone buy a mode C transponder when for only a little more
one can buy a mode S unit?

Andy




Actually the 10 year life is not completely accurate, even if I agree
a bit with probably the sentiment behind it. I just don't want any
glider pilots with Mode C transponders to think their transponders
have an abslute hard limit where they stop being useful in 10 years.

Mode C transponders are usable it the USA well beyond 10 years - but
to meet the 2020 ADS-B data-out carriage requirement (a requirement
for power aircraft in similar airspace as transponders are required
now) you would need to add a UAT transmitter or replace the
transponder with a Mode S with 1090ES data-out. Right now its
impractical from a cost, STC paperwork hassle (on non-experimental)
and final -B rev compliance requirements on many products, to add ADS-
B data-out to most light aircraft or gliders but you can install a
Trig TT21 and in future update the firmware and add the ADS-B data-out
GPS.

How current aircraft owners manage the transition to the 2020 ADS-B
data-out mandate will be interesting to see - i.e. whether Mode C
equipped aircraft add UAT devices or swap out their transponders to
get new Mode S units with 1090ES data-out. I expect many will take the
transponder upgrade route since it is a chance to refresh older
transponders which they still need to carry (in may owner aircraft)
and older transponders can become a maintenance liability, so why not
refresh both in one box? For newer Mode C transponders there exists
more of an argument to add a UAT device. In the glider community in
the USA with PowerFLARM looking like important and popular technology
Mode S 1090ES data-out is a better technology to consider than UAT
data-out.

Darryl