Maintenance
I think you'll find that O'Leary/Ryanair do "capitalise" major maintenance, and write it off over the period to the next maintenance of that type. It's only a timing difference in the Profit & Loss account, but keep expanding the fleet and the timing difference grows. Once the fleet size stabilises I'd expect the timing differences to reverse.
I suspect it's not the only airline doing that.
Sorry, off topic from the main thread, but I'm an accountant with an interest in aviation.