Low-cost airline Ryanair will shut down its website for three days to upgrade its reservations system.
Ryanair says new software will allow up to 200 million bookings a year
Customers will not be able to book flights from 2200 GMT on 22 February until 2300 GMT on 25 February.
Ryanair says its current system is close to "breaking point" and the new software is needed to handle bookings.
The shutdown will also allow it to comply with an order by UK market regulators to make prices on its website clearer to consumers.
Last August, the Office of Fair Trading (OFT) ordered 13 airlines to amend their websites to include "fixed non-optional" costs in their headline fares.
Ryanair has been the slowest to comply with that ruling, blaming technical difficulties.
The OFT extended its deadline for the changes from 31 January to 15 February.
"We are very disappointed that Ryanair has not met the agreed date of 31 January for changing its website," the OFT said in a statement.
"Ryanair has informed us that the changeover to its new system will be on 22 February." it added.
Ryanair takes 90% of bookings through its website.
But a company spokesman said the shutdown, "will not have an effect on bookings, loads or financial results."
Last week, Ryanair warned that profits could be halved this year as fuel costs rise and the UK pound weakens.
The warning came as the budget airline reported that net profit dropped 27% to 35m euros ($52m; £26m) during the three months to the end of December.