British Airways took another hit during its critical summer travel season after an information technology system outage forced the cancellation of more than 90 short-haul flights on Wednesday across three London airports.

More than 80 flights were scrapped at Heathrow Airport and at least another 10 at Gatwick, according to a spokeswoman. Some 200 other flights were delayed, with London City Airport also affected.

The carrier had to switch to back-up manual systems to keep the remaining flights operating, while offering customers refunds or the chance to rebook flights from Thursday, according to an emailed statement.

“We are working as quickly as possible to resolve a systems issue which has resulted in a number of cancellations and delays today,” BA said. “A number of flights continue to operate.” The airline urged passengers to check the status of their planned journey before traveling to the airport.

BA has already faced flight disruptions this summer from baggage issues, another system glitch, and the threat of a strike earlier this week by Heathrow Airport workers, which was called off at the last minute. The carrier is due to restart talks with pilots on Thursday in a last-ditch attempt to avoid a walkout that could come as soon as the end of this month.