Originally Posted by
Bluestar
The vast majority of airport subsidies to airlines such as Ryanair are not PSOs, just "ordinary" start-up aid for new routes, and there are specific conditions under which this aid is allowed (e.g. the funding is open to any carrier, it diminishes over time, it's for a maximum of 3 or 5 years depending on the region, the route has a realistic prospect of sustainability after the aid runs out, etc.)
But in many cases the subvention comes from sources outside the airport, and shouldn't really be lumped under "airport subsidies". Regional and national tourism promoters may feel that paying an airline for delivering tourists to their patch is a rational and efficient use of cash raised through taxation or from their members. There's no point rehearsing here the arguments supporting the economic stimulation provided by air transport.
The conditions you refer to apply to an airport's structuring of an incentive scheme to attract new carriers and/or promote new routes. That a regional tourist authority bungs FR a couple of euros for each passenger it brings to its airports, or gives the airline a wadge of cash to assist in marketing its services to those airports - well, that's another story.