Ryanair’s website and mobile app will close for 12 hours for a systems upgrade later this week.
The airline is warning customers they will not be able to access either from 17:00hrs (UK time) on Wednesday November 7 until 05:00hrs Thursday.
Its online check-in service will also not be available during this period.
Ryanair said it has already contacted customers booked to travel on the affected days by email and SMS text to advise them to check-in online for their flight on Tuesday.
New bookings or changes to existing flights will not be possible during this web closure.
Head of communications Robin Kiely said: "We sincerely apologise for any inconvenience caused by this upgrade, which will further improve Ryanair.com, Europe’s largest travel website."
