jet vs jet crash in brazil - 155 likely dead

Martin Gregorie wrote:[snip] - if a mode ES transponder is not
receiving interrogation pulses,
does it still output the periodic squitter burst?

Martin, I expect an expert will answer definitively, but ages ago I
picked up this quote which explains it in lay terms:

"Mode S 'Announcement'. (thats not its proper name, which I forget, but
conveys what it does). The transponder radiates a signal announcing its
presence, to other mode S capable radar equipment in the area, about
once a second.

This signal contains a unique identifying 'Mode S Address'. This
address is hardwired into the aircraft, and unique to the aircraft.
I.E. no other aircraft, anywhere in the world, will have the same
address.

Note that this announcement is made unprompted, i.e. the transponder
does not wait to be interrogated, it just sends the signal anyway.

TCAS listens out for these announcement signals, and builds what is
called a "Roll Call" of Mode S transponders in the area."

(Furthermore, TCAS/TCAS dialogue takes place to resolve conflicts,
without any ground/ATC SSR activation. The TCAS units squitter at each
other. If TCAS detects a transponder which is not TCAS related, e.g.
in a glider, it alerts the TCAS-equipped pilot to resolve the conflict
without dialogue with the non-TCAS transponder, just using the latter's
position and height data as squittered.)

Chris N.