Originally Posted by punkalouver
I direct you to the Eurocontrol ACAS Bulletin #9 and quote...
" 5. The factor of collision risk reduction thanks to TCAS II in the operational world, taking into account some non TCAS II equipped aircraft, inaccurate pilot responses and lack of responses, altitude reporting inaccuracies, etc."
Reading your quote I thought this was point "5" from an enumeration of various points. The meaning, however, is that TCAS has reduced the risk of a mid-air collision by a factor of
FIVE.
And I'm sure they arrived at this figure by finding out that there were 80% fewer mid-air collisions since the mandatory introduction of ACAS-II per billion flight hours, compared to before. Or did they?
Otherwise, this figure is completely bogus. (I'm certain it is bogus anyway, since luckily the number of mid-air collisions is too low to derive any statistical significance from it.)
There have been some irresponsible statements made much earlier in this thread. It is rational to Follow The RA even if it contradicts an ATC instruction.
Trying not to re-iterate the entire argument: we did not doubt that following the RA was a rational choice. The point was that it was neither the only rational choice, nor necessarily the best (as the DHL reaction clearly shows: they followed the RA, and had a mid-air collision. QED).
Bernd