The 12-hour shutdown means that bookings, changes and online check-in will not be possible.
Ryanair is warning it will shut down its website and mobile app for 12 hours this week to allow for a systems upgrade.
The low-cost carrier is telling passengers they will not be able to make bookings or check-in during the downtime. Yet its fee for airport check-in will apply during the outage, according to the travel trade site TTG.
The airline’s web and app services will be offline from 17:00 UK time on Wednesday until 05:00 on Thursday.
It apologised to passengers for the inconvenience and urged them to ensure they complete in advance any necessary actions, such as check-in.
Ryanair operates a 48-hour check-in window before departure for passengers who have not paid for seats or priority boarding.
Ryanair says it has already contacted all customers booked to travel on Wednesday and Thursday by email and SMS text, advising them to check-in online on Tuesday, before the closure takes place.
“As part of our continued digital development, a web closure and system upgrade will take place for 12 hours from 1700 (UK time) on Wednesday November 7 until 0500 (UK time) on Thursday November 8, during which time our online check-in service will not be available,” a Ryanair statement reads.
“Flight bookings and changes will also be unavailable during this period. Customers travelling on Wednesday or Thursday should check in for their flight on Tuesday November 6.
It continues: “We sincerely apologise for any inconvenience caused by this upgrade, which will further improve Ryanair.com, Europe’s largest travel website.
In related news, Ryanair is reporting an 11% rise in traffic during October to 13.1 million passengers. The total includes 500,000 passengers at Lauda, the carrier founded by former Formula 1 champion Niki Lauda and recently bought by Ryanair.
During the month the airline had to cancel around 300 flights due to a ground handler strike in Brussels, bad weather and ongoing air traffic control employee shortages in the UK, Germany and France.
Germany’s VC pilots union, meanwhile, says it cannot rule out more strikes at Ryanair, the BBC reports.