Ryanair will cancel almost 18,000 flights from November to March affecting around 400,000 passengers.
It will fly 25 less aircraft from November, and 10 fewer aircraft from April 2018.
The low-cost airline said it would roster all of the extra pilot leave necessary in October, November and December to meet the IAA’s requirement to complete a nine month annual leave transition period so it can start a new calendar leave year from January 1.
Customers are being given between five weeks and five months notice to change flights or receive a refund. They have also been given a €40 (€80 return) travel voucher which will allow them to book a flight during October on any Ryanair service taken between October and March 2018.
Ryanair cancelled 2,100 flights in September and October due to its pilot rostering problem.
The airline has blamed the summer cancellations on “messing up” pilot holiday rosters and again denied it had a pilot shortage.
Chief executive Michael O’Leary said: “We sincerely apologise to those customers who have been affected by last week’s flight cancellations, or these sensible schedule changes announced today. While over 99% of our 129m customers will not have been affected by any cancellations or disruptions, we deeply regret any doubt we caused existing customers last week about Ryanair’s reliability, or the risk of further cancellations.
“From today, there will be no more rostering related flight cancellations this winter or in summer 2018. Slower growth this winter, will create lots of spare aircraft and crews which will allow us to manage the exceptional volumes of annual leave we committed to delivering in the 9 months to Dec 2017.”