Clearway must be within the Airport boundary
kungfu panda, I agree that clearway must be "under control of the airport authority" but in the UK (as the definition in CAP 168 which I have quoted above shows) it does not have to be within the airport boundary.
Under "control of the airport authority" and "within the airport boundary" are not necessarily the same thing.
Semantics I know but I can think of one or two airports in the UK (including BRS) where the clearway extends outside the airport boundary.