A fascinating discussion.
Eurocontrol has been studying this subject (common transition altitude) for over three years as far as I'm aware, and failed miserably to come up with a solution. Best they (41 member ECAC States) could agree on was a "regional CTA" but still that has not seen the light of day. So much for consensus.
But if you wish to get a better understanding of the issues and problems, then consider that some aerodromes (e.g. Lugarno) have 2 T/A's - one for each runway end, whilst some/most Eastern European States apply a different T/A for each runway direction - I.e 3 runways = 6 T/A. Now to spice it up a bit more, try Bulgaria where they specify "Transition Height"- I.e based on QFE.
Need more!!
