British Airways canceled nearly 60 percent of its flights on May 27 when an IT outage knocked out the airline's systems and stranded 75,000 people over a holiday weekend.
The airline canceled 479 flights or 59 percent of its operations on May 27 and 193 flights or 23 percent of its operations on May 28, its parent International Consolidated Airlines Group said.
It blamed a power surge that knocked out its computer system, disrupting flight operations, call centers and its website.
The flights resumed on May 30 but the company has faced increasing pressure over its response to the IT failure and IAG chief executive said on Monday that British Airways had commissioned an independent study into the shutdown.
"British Airways is working hard to compensate affected passengers as quickly as possible," said IAG, which also includes Spanish airlines Vueling and Iberia as well as Ireland's Aer Lingus.
Prime Minister Theresa May had called on British Airways last week to compensate the thousands of passengers who were left stranded.
British Airways' traffic, measured in revenue passenger kilometers, fell 1.8 percent in May, while it rose by 1.8 percent for the group as a whole.
The group's capacity, measured in available seat kilometers, rose by 0.9 percent in May, while for British Airways it fell 1.9 percent.
(Reporting by Arathy S Nair in Bengaluru. Editing by Jane Merriman)