CAA rules have long prescribed that the number of wet-leased aircraft in an AOC holder's fleet cannot exceed 50% of your core aircraft fleet. If you have one aircraft on the UK register and try to secure permission to wet-lease 15 others - even on a part-time basis - then you can expect to fall foul of this provision, which has been in place for longer than I can remember with the objective of making sure that UK AOCs cannot effectively become flags of convenience. I would be very surprised if the CAA had not outlined that to Ryanair. Unlike Wizz (for example) which has a meaningful and growing number of G- aircraft on its UK AOC, Ryanair look to have gained the approvals and promptly done very little with them.