For me it seems to be one of two major problems that BHX has.
Firstly keeping routes and airlines beyond a season or two! I can't think of another airport that comes anywhere close to BHX when it comes to losing so many routes as quickly as they arrive. The second is as above, working with airlines to maintain a steady and consistent growth. Too many just stagnate!
For me the perfect example of a success story is easyjet at Bristol. They have been adding an aircraft or two every year for a while now and have grown network of routes that we can only dream about BHX even coming close to having.
For BHX it seems to be all about Jet2 at the moment so we'll have to see if they fancy a bit more of a dabble into the city break market and whether they can be persuaded to try the likes of Lisbon, Athens, Valencia, Reykjavik etc. If not I fear we may have some very lean years ahead of us.