Winter
Ryanair had for many years been able to fly at very low cost over the winter and make small profits on many routes all year.
higher costs means that filling planes at very low seat prices makes a loss in winter. Ryanair is losing a lot of the off peak traffic that made the buisness model work so well 5 years ago. He has also lost the ablity to buy planes for so much less than he could sell them for after a few years. The owned planes could suffer a big write down in value on sale. The alternative is for him to fly an aging fleet. Others like Easyjet could then get the next generation of planes and overtake MOL.