But the low-cost carrier’s annual traffic has risen 5.1 per cent to 76.4m in spite of the bigger-than-usual stoppages.
Ryanair’s load factor, a measure of how many available seats are paid for on its flights, slipped one percentage point to 79 per cent last month.
British Airways parent IAG fared better in December, with passenger numbers up 10 per cent to 3.88m after a boom in European and North American flights, as well as better weather conditions than last year.
IAG said traffic in 2011 rose 2.1 per cent overall, with a jump in passengers across the Americas offsetting a 12.5 per cent tumble in UK and Spanish domestic flights.
Its cargo division also enjoyed a 6.4 per cent rise in annual revenues.