ATC Watcher/jondc9
ATC
I do not believe you should lump together "ATC and (T)ACAS" as the two primary anti-collision systems. This , of course, is not true. They are not co-equals. ATC is the primary collision avoidance system ....that is its primary role, ie, separation.... other than eyeballs (which is interesting since there has been no discussion of looking out the window...have we given this up because of closure rates or other factors for all aircraft at flight levels above 180 ?)
what is becoming more and more obvious......
ATC cleared both aircraft to the same level without proper coordination between adjoining sectors. Through inadvertence, complicated by possible flaws in its procedures, equipment performance or design, ATC was neither able to recognize the nature of the situation that was unfolding and communicate this to other sectors nor communicate with the Legacy to issue an appropriate clearance or confirm its level. Contributing factors were poor communictions coverage and failure or improper operation of the transponder aboard the Legacy.
jondc9
your characterization of the twelve calls as being sufficient cause to select
7600 does not consider that those calls occurred in 4 minute period(not very long in this environment) followed by what probably appeared to them as a response from ATC to their calls (which, in fact, appears to have been a blind call from ATC) requesting that they change frequency. I suggest that the lost-comm situation began following the crew's subsequent unsuccessful attempts to contact ATC....just two minutes or so before impact. At this point the ATC controller should have been on the horn to the next sector controller (who was in contact with GOL) advising of the NORDO Legacy at an unconfirmed FL360. Since the collision occurred at or near the sector boundary, it will be interesting to learn whether the Brasilia controller had the GOL flight on his display and for how long.