I think the issue is that Ryanair went for de-rated engines on the 737-800s which give them benefits in terms of lower maintenance costs. The drawback is that they need longer runways and hence Ryanair have been going round beating airports up to extend their runways, in some cases they have - I think Lubeck is one example. In Derry's case it's not so easy as they are owned by Derry City Council and require funding from both the UK and Irish governments to carry out such work, not to mention the effect on local residents.