Originally Posted by 17thhour
Yes im referring to Trevor Thom, and what, are you not agreeing with what is being said? It makes sense to me and theres noting in the AIP or legislation about it, just like the quadrantle rule is optional for VFR, we still do it even though its not "legislation."-well some of us do anyway.
Your comments, and the extract that you refer to may be considered to be good practise.
The real problem is that for all that may be good or bad about the rest of the book, the extract that you reproduce is mixing two different issues. The pilot of an aircraft flying under VFR without receiving any form of air traffic control service is responsible for
collision avoidance - this is achieved through a combination of techniques and good practises including awareness of the implications of differing altimeter settings.
Separation is an ATC function and is something that the controller provides. In the vertical plane, the separation that is normally applied is 1000ft or more - the controller will use a variety of techniques to ensure that this minimum vertical separation is achieved, regardless of the altimeter settings that are used by the aircraft concerned.
In a known traffic environment the controller may instruct an aircraft to fly at an altitude above the Transition Altitude, or at a FL when below the Transition level, or may instruct an aircraft to fly level in the Transition Level. Such clearances may not be good practise (or may not be possible for other reasons) but the point is that it's up to the controller how he or she manages the traffic in order to achieve vertical separation when it's required.
Mr Thom sadly mixes what some may consider to be a good idea (for collision avoidance staying 500ft above other aircraft seems to be a good idea if you can do it), with the ATC function which provides separation (and where 500ft usually will not be 'satisfactory'!).