Sort out public transport links
Durham Tees Valley Airport (or "Teesside" as the Ryanair crew I flew in with last week still called it) is neither one thing nor the other at the moment. It is not a business airport, as Aberdeen and Amsterdam are not enough - add London (any), Paris, Brussels and Frankfurt to qualify in my view; and it is not a low-fares carrier airport - as low-fare-paying passengers won't want to pay more for a taxi to Darlington than they did for their airfare from Dublin or Spain (or Poland, when WizzAir flew in).
The trouble is, the bulk of the interlining business traffic is adequately served by AMS and there is not enough passenger demand to justify further dedicated services. And for low-fare passengers, the public transport options are just woeful. Ryanair passengers through Beauvais and Skavsta are brought to and from the airport by dedicated bus services, using modern comfortable buses, and pay reasonable fares. That just wouldn't work from MME, as it serves Redcar, Northallerton, Sedgefield, as well as Middlesbrough, Darlington, Stockton, and, allegedly, Durham. That's just too many destinations for public transport to serve on a bus-per-flight basis.
I wondered if making the airport a sub-regional transport hub with a bus interchange, train services and good road links might work, but I doubt it will happen: too many conflicting interests, I suppose. How about giving it to the RAF (or USAF!)?