I am sure this has been answered before, but how do Ryanair work the self employed angle? Generally, if you register yourself self employed then the responsibility will lie with you to satisfy the legal requirements for that condition.
If Ryanair allow you to work for other people during the year, and you do that, amongst other requirements that should be ok. Do Ryanair allow you to work in your month off for example, free of their control? Do they allow you to work outside of your rostered period?