TT21 operation with no ICAO address

On Dec 9, 6:58*am, Andy wrote:
I'm moving this to a new thread since it has nothing to do with the
requirement for altimeter TSO.

I asked what happened if a mode S transponder was installed without an
ICAO address. *That was a sort of tongue in cheek reaction to the idea
that someone would not want their tail number broadcast to the Feds.

Darryl responded:

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 like to continue that discussion.

Isn't it true that a mode S capable transponder cannot respond to a
mode S interrogation if it has no valid ICAO address?

Isn't it also true that a mode S transponder is also required to
respond to both mode A and mode C interrogations.

If both are true then doesn't it follow that a mode S transponder such
as the Trig TT21, if installed with no ICAO address, will not respond
to mode S interrogations but will respond to all mode A and mode C
interrogations.

If that is indeed the case then any new transponder purchaser who
wanted mode S capability in the future, but was paranoid about
broadcasting the tail number, could disable mode S responses by
leaving the ICAO address entry blank and use it just like a mode C
transponder.

Andy

Not to derail your discussion, but why does the notion of
"broadcasting your tail number to the feds" keep coming up? It seems
to indicate either paranoia or illegal activity. Is there some other
reason to be concerned about that?

On Dec 9, 7:02*am, Westbender wrote:
It seems
to indicate either paranoia or illegal activity. Is there some other
reason to be concerned about that?

Aren't those two reasons sufficient? No others that I know of.

Andy

On Dec 9, 8:50*am, Andy wrote:
On Dec 9, 7:02*am, Westbender wrote:

It seems
to indicate either paranoia or illegal activity. Is there some other
reason to be concerned about that?

Aren't those two reasons sufficient? *No others that I know of.

Andy

Is this a common concern among sailplane pilots? I'm just trying to
understand the thought process behind someone wanting to fly
"anonomously" with a Mode S transponder. I don't think sailplanes
would be much good for smuggling or terrorism. The only reasonable
intent I can think of is that people don't want to be identified when
wandering into airspace they shouldn't be in. What am I missing?

On 12/9/2010 8:18 AM, Westbender wrote:
On Dec 9, 8:50 am, wrote:
On Dec 9, 7:02 am, wrote:

It seems
to indicate either paranoia or illegal activity. Is there some other
reason to be concerned about that?

Aren't those two reasons sufficient? No others that I know of.

Andy

Is this a common concern among sailplane pilots? I'm just trying to
understand the thought process behind someone wanting to fly
"anonomously" with a Mode S transponder. I don't think sailplanes
would be much good for smuggling or terrorism. The only reasonable
intent I can think of is that people don't want to be identified when
wandering into airspace they shouldn't be in. What am I missing?

If you wander into airspace you shouldn't be in, broadcasting your
position with Mode C, would you be left alone? In R or P airspace, I'm
pretty sure someone comes looking for you, but how about A, B, C, and D?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl
- "A Guide to Self-launching Sailplane Operation Mar/2004" Much of what
you need to know tinyurl.com/yfs7tnz

On Dec 9, 6:08*pm, Eric Greenwell wrote:

If you wander into airspace you shouldn't be in, broadcasting your
position with Mode C, would you be left alone? In R or P airspace, I'm
pretty sure someone comes looking for you, but how about A, B, C, and D?

I have first hand experience of being asked to "call the tower" after
an inadvertent class D incursion. I was not pilot in command at the
time.

I also had a "call approach control" after our malfunctioning encoder
made Phoenix approach think we had busted class B and caused a few
airliners to take evasive action. Again I wasn't PIC but as the holder
of the higher ratings would have been implicated. In this case it
seems that 2 transponder returns had been mixed up when another
aircraft came very close to us and the Class B violation was the other
aircraft and independent of our erroneous altitude squawk. It was good
that I had a Garmin track log and could prove we had not been where
they said we had been. Even better that our controlled passage of a
local class D was not consistent with the position of the violation
and that was all on the tower tapes.

Bottom like is, if they see you doing something wrong they'll try to
track the transponder to a point where they can identify and talk to
you. This may explain some sudden transponder failures.

Andy