ACAS v ATC
Have just been reading a very interesting article in "Feedback" about following ATC instruction or ACAS, which is still a hot topic after the Swiss accident.
Being non-confidential I won't copy the whole article here, but, for those who didn't, haven't or can't get a copy it concerns an RT exchange between controller and pilot over Northern Europe during which an "Immediate" descent restriction was given followed by traffic information and an instruction to ignore any instructions given by ACAS!
Although it made me wince on first reading it the article does raise an interesting question - that being at what point, after noticing a potential loss of separation does the full responsibility remain with us to "save the day"?
In en route, for example, aircraft are travelling at upwards of 8 miles a minute and any restriction or instruction issued is going to take time to happen, the laws of physics state that.
Here's an example;
2 aircraft on crossing tracks, converging, at the same level. If the aircraft are, say, 30 miles from the crossing point when I notice the confliction I would have no hesitation in issueing an instruction to move one of the planes.
If the same planes were 20 miles from crossing I would still issue an instruction but may sound more urgent with my delivery!
If the planes are 15 miles apart, I hope I may even give traffic information and "avoiding action"
If the planes are 10 miles apart my instinct would be to do the above but now, in the back of my mind is the nagging suspicion that - as I can only talk to one of them at a time, if I do give avoiding action to the first, has the second began to respond to ACAS already?
It's a fine line but it's position is unclear. I fully understand that once issued with an RA a pilot must follow it, even if it contradicts ATC, but when exactly will that happen?