I'm not sure this is correct, since it is not clear if the airline passes the money on or not. Are the airport fees based on the amount they pay the airport or the normal fee regardless of any negotiation (ie are Ryanair inflating the airport fee?).
Brabazon: you're right to be suspicious; the airport fees are usually based on the
published tariff, not the one the airline actually pays.
I've experienced this in negotiating with airports:
Airport marketer: "OK, our published rate is £5 per passenger, but we'll give you 50% off, but in your website booking engine you can still show £5 as the airport charges, so you'll make a couple of quid extra yield."
(Can't remember if the number was £5, but you get the idea.)
This obviously works best as a yield-booster if the taxes-and-charges are kept unbundled until late in the booking process, i.e. let's sucker the punter in with an apparently low fare and then back-load it with all these "extra charges" only after he's chosen particular flights and is feeling a bit more committed.
I wonder whether any consumer watchdog or regulator would be interested in checking that the apparent "taxes and charges" really are at the levels imposed by third parties?