Apology accepted.
Now...
there are any number of reason that an aircraft may change track while on "own Nav", the risks of which are greatly diminished by the use of parallel headings
Who was talking about parallel headings? The example was a/c on own nav (laterally separated) being put on headings to "assure" sep. You see, I don't think you can support that position with any actual
evidence .
Prove it. All I ever get in reply is "well, it's common sense". Where is it stated
anywhere that a/c on own nav can divert around wx, track to mysterious intermediate waypoints etc etc? The pilots aren't handflying anymore. If they are told to track direct XXXXX, then they push buttons and the a/c does it. Doing anything else requires intervention. As I have stated over and over, I have seen just as many a/c divert around wx while on own nav, as on an assigned heading. If you are under the misapprehension that an a/c on an assigned heading will not divert, then you are setting yourself up for a fall. As I previously said, if pilots are under the misapprehension that if on own nav, they can divert, then that is something that ATC has probably fostered and needs correction.
If you are going to argue that the a/c may not track to XXXXX due to database errors, pilot error, etc etc, it's no different to an assigned heading error. If you don't check the tracking before 'setting and forgetting', it's the same as assigning a heading and not checking.
we are not only required to provide separation but to ASSURE it
Furthermore, if a/c are changing level, I don't think you can
assure anything with headings. See earlier posts. You even acknowledge that you don't know how much wind shear would be required for you to lose separation in your example (and it would depend on the time involved ie rate of level change). More to the point, we don't plan/buffer for failure of altimeters or transponders, and the a/c are far closer together there. Why do it for 7nm lateral sep (that the a/c will achieve without our intervention)?
As I said, times have changed.
multiple previous validations in the Uk albeit before any "track to " separation was acceptable. (maybe I'm getting too old!)
Maybe it's time to rethink some of these techniques. Alas, I find many minds are closed on the subject (except maybe the people writing those "track sep" procedures in the UK you aren't aware of, Guy
).