Originally Posted by
Lead Balloon
Errm, could you quote the current rules that require the margin to be planned?
There are none. You can operate right up to the boundary.
AIP ENR 1.1 2.1.2
Note 2: For aircraft operating in close proximity to an airspace boundary where there is a risk of an airspace infringement, the pilot in command should consider obtaining a clearance to enter the airspace or altering track to remain well clear.
There's absolutely nothing about not planning through CTA in AIP. Just don't enter it without a clearance.