Firstly my condolences to all concerned.
[/QUOTE] Cause 5. Bad luck. Even though both a/c were descending at the time of the collision, an accident was by no means inevitable as has been suggested on the TV news tonight. The chances of a collision were still small, especially since visibility was good. Instead of the catastrophe that happened, we would probably not find out about the incident for some time and it would be 'just another airprox incident'. [/QUOTE]
In aviation there is no such thing as "Bad Luck".
It is perhaps ironic that the swiss cheese simile is used in our Flight Safety forums but sadly it is no less pertinent when the holes line up as they have here. There is obviously a chain of events which could have been broken at any stage from Flight Planning to the final manoeuvres of both aircraft. Many valid points have come out of this forum already without the speculation of what the respective crews may or may not have reacted to. Those professional amongst us will recognise these points without me re-iterating them again. But for my tuppence worth:
TCAS is not infallible but assuming it was working correctly, it has a perceptable lag time in resolving a DESCEND RA to a CLIMB, add the pilots reaction time and the time to change a 90+ ton aircraft's flight path and it all adds up to getting too close for comfort. Yes, believe and react to TCAS but it should be a last line of defence. I find it inconceivable that there was no lateral separation instruction issued by ATC or requested by either aircaft. Personally, if I get TCAS traffic at the same level on an apparent intercept I would query it well before it got to a TA or RA. I would also be aquiring it visually(assuming VMC).
The case mentioned by Pontious? was BA & Pakistan 747s over the Indian ocean, I think, both at their correct opposite FLs except the PAL 747 TCAS had a bent pin resulting in an incorrect alt input to the TCAS telling it that both a/c were co-alt. TCAS did its thing and instructed PAL to climb (up to BAs level) and BA to descend (down to PALs level) Collision avoided as PALs TCAS switched Alt bands as it climbed and thus fed correct inputs plus to the A/C were visual. The kit may be good but it should be used in conjunction with the "Big Picture".
I'm sorry, but I do not believe these two aircraft should have been placed in that situation on a quiet night in the first place. Having been done so consequent actions are open to debate but it does behove all of us to place ourselves in either cockpit and ask "what would I do?"
God Bless all