So in a nutshell...
Eurocontrol assumed that, if it could prove RVSM was safe even without ACAS, it would not need to prove that it was safe with ACAS...because use of ACAS automatically makes the skies even safer.
But (says the good professor) the use of ACAS contributed directly to the German collision.
Therefore the Eurocontrol assumption that ACAS makes the sky safer is incorrect. Therefore the "non-ACAS" RVSM safety case cannot automatically be applied to the "with-ACAS" RVSM situation.
I think you have to examine whether Prof Ladkin's assumption over ACAS and the German mid-air actually stands up to scrutiny. He claims that if the DHL 757 hadn't followed ACAS procedures the collision wouldn't have happened.
While this is true in its absolute sense, I think it's unreasonable to disregard the inappropriate ACAS response of the Tu-154 -- you can't construct a logical argument on safety if the foundation of the argument fails to build on existing rules (in this case the procedures following an ACAS advisory). Else you could assume that pilots won't follow ANY safety procedures correctly -- in which case, your safety case is shot to !!!!! before you even begin.
Just as a side note: since both aircraft were initially at the same altitude (FL360) the vertical separation between flight levels was irrelevant. The collision would have occurred whether the VSM was 1000ft or 1000 miles.
Last edited by Kalium Chloride; 29th August 2002 at 22:12.