I'm surprised this only seems to be a problem at Derry. As I understand it (I'm not that technically minded with regards to a/c ops), the 737-800s that FR use are extremely efficient, but their engine configurations don't give them the power to get off some of the shorter runways, even though this is less of a problem for an A319, or even a 737-700.
That would be fine if they stuck to main airports, but we all know they don't. I would have thought that the smaller regional airports would be less likely to have runways with a decent length - or is it more a case that the places with constraints are the older airports which are closer to city centres (SOU etc), where FR wouldn't want to go anyway?
Does that mean that there is an even larger untapped market for a regional loco to come in with an economical but smaller a/c, such as the Q400?