On Dec 8, 12:37*pm, Andy wrote:
On Dec 8, 1:03*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.

Ok, valid points.

I just checked with my local avionics shop. $95 for mode C and $125
for mode S. Not a deal breaker for me.

As to broadcasting the tail number *- the TT21 installation menus
allow the aircraft ICAO code and the registration to be set but I
don't think there is an equipment requirement for them to be set. *In
other words I think it will work if the defaults are left unchanged.
Is there any regulation that requires a mode S transponder to transmit
that data in US?

Andy

A Mode S transponder absolutely has to transmit the aircraft ICAO
address, a correctly configured ICAO address is required for the
transponder to actually work--bad things might happen if two aircraft
had the same default ICAO address were being interrogated at the same
time.

I am not sure where else this is captured in the regulations, but
checking this is a requirement at install and during the biannual
"Part 43 Appendix F" test.

Part 43 Appendix F...

(f) Mode S Address: Interrogate the Mode S transponder and verify that
it replies only to its assigned address. Use the correct address and
at least two incorrect addresses. The interrogations should be made at
a nominal rate of 50 interrogations per second.

---

I can't find it quickly in the regs but it may just be that the
requirement in 14CFR 91.215 (b) to operate in compliance with TSO
C-112 (which then captures you the pilot and not just the manufacturer
and that TSO's incorporation of RTCA DO-181 which may spell out the
Mode S address requirement). There better be an overriding
requirement, otherwise somebody could argue a pilot can can just
change it at any time. Yes its the off season but I'm not so bored yet
to fully follow this though.

Please be very careful here. Make sure your Mode S transponder is
using the correct ICAO address (the one registered to your aircraft).
If you really think you are goign to be doing bad things within view
of ATC then maybe you should rethink how you are flying.

Darryl