Originally Posted by
mutley320
Turning off track/airway is the best way to go, as all the procedures state but my resistance to it (in busy controlled airspace) without communication with ATC, is that nowadays you spend large amounts of time on Radar Headings or indeed direct routings that aren't "on airway."
So i'd love to hear an opinion from NATS or EURO control.
I think that is quite understandable. Why not give it a second tought.
1) The procedure I quote is ICAO "differencies to Europe". While I agree that is is a great shame that ICAO documents are not available as public domain, the sad status quo is that I cannot give you a link. Yet, the quote says
as a controlled flight. In other parts of the document, the word
Eurocontrol is quoted numerous times. I get the feeling, that whoever designed this procedure (
if able!) and codified it, had a very good European ATC input.
2) The headings you mention, as I see it, serve to make the full use of available airspace by reducing separation to the approved standard of 5 NM. TCAS threshold is 1,1 NM /35 s for RA whichever comes sooner (now I've found it). 420 kt TAS is 7 NM/min.
Let 5 NM separation be the "paperwork" threshold.
Let 1,1 NM / 35s be the "scary-hairy RA" threshold.
Let 0 NM be the ultimate threshold.
If you are kept on a heading to achieve separation 5 NM to a conflicting (same level) traffic, in a 90° scenario it would take you 42 second to hit it. This may very well be the the start of your Emergency Descent, so the everage RoD is about 2000 fpm in the first minute. Target ACAS RA miss vertical distance (now I've found this as well) is 600 ft. By the time you reach the ultimate threshold - 42 seconds, you would have achieved more than twice (1200') the ACAS life guard separation.
Discussion regarding the other two threshold is, I'd say,
superfluous. Needless to say, ATC will definitely NOT be happy about an ED. Yet, neither them nor us are payed to feel so, as opposed to finding and exploiting the safest course of action, retaining as much margin as operationally available.
There is a procedure. It may not be the optimal thing to do ad-hoc, but it will save our (a-word) and cover our (b-word).
A procedure must be
simple, short, unific, and uniqe. At the end of the day, it is the pilot's call.
Cheers,
FD
(the un-real)