At the risk of wading in to what looks like a really messy workplace dispute...readers might be interested to know that Ryan Air may well have a contractual right to cancel pilot holiday.  

Well drafted contractual holiday provisions will often give employers the right to cancel holidays, or indeed instruct employees when to take holidays, to cope with fluctuations in demands. 

However, as with any such contractual powers, employers must exercise them reasonably, or risk breaching employees' trust and confidence.