The problem with the marginal regional airports is that you can't get the required yields simply because the catchments aren't big enough
This reminds me of a discussion on this topic I heard before.
Basically it was that it is relatively easy to generate a profit flying from somewhere(DUB,STN) to nowhere,as was the case in the early days of MOL's Ryanair,
Its when you start flying from nowhere to nowhere, that profitabilty gets trickier...Probably safer not to give an example for this one!
