Shares in the parent company of British Airways fell today after a huge IT failure left 75,000 passengers stranded over a bank holiday weekend.
The IT failure came as a major blow to an airline that once marketed itself as "the world's favourite".
BA had to cancel all flights from London's Heathrow, Europe's busiest airport, and Gatwick on Saturday after a power surge knocked out its computer system, disrupting flight operations, call centres and its website.
Problems continued over the long weekend, and although BA said it expected to run a full schedule from Heathrow and Gatwick today, it was left with work to do to in the longer term to restore its reputation.
BA had already come under fire for charging extra for food and baggage and the sight of stranded passengers trying to sleep on the floor of its gleaming Heathrow Terminal 5 building had the potential to do huge damage to its brand.
Like other European full-service airlines, BA is facing increased competition from budget rivals Ryanair and EasyJet.
BA's chief executive Alex Cruz had said yesterday that the power surge was so strong that it also rendered the back-up systems ineffective.
Cruz denied a suggestion from the local GMB union that the outage was linked to a decision to cut staff numbers and outsource work to India.
"British Airways' IT failure over the weekend is clearly a PR nightmare and will take a real focus in terms of handling customer's complaints and compensations claims in order to rebuild trust and confidence with the public," analysts at Goodbody said.
They estimated the cost of the outage at €82m.
Ryanair chief executive Michael O'Leary said his company saw very strong bookings over the weekend, but added it was unclear if this was related to the BA problems.
Ryanair, which reported record annual profits earlier today, said it had systems in place to avoid a similar fiasco.
"We have three IT locations in different countries across Europe," Kenny Jacobs, chief marketing officer, told reporters in London.
"If there's a power surge at one, the second kicks in, and the third one would kick in. That's what most businesses would do. That's our approach and we've never had a major outage," he added.
Shares in BA's parent company IAG, which also owns carriers Aer Lingus, Iberia and Vueling, fell as much as 4.5% at one stage today, the first day of London trading this week. They closed over 1% lower this evening.
Flight compensation website Flightright.com said around 800 flights had been cancelled at Gatwick and Heathrow over the weekend. BA did not comment on the number of cancellations.
Analysts at Deutsche Bank estimated that the costs of compensating passengers would be around €47m and that the cost of restoring BA's network had an upper limit of €15m.
But they said that IAG's management has been investing in renewing its IT systems, and expected customers to return to BA quickly as the incident was a "one-off".
"Whilst clearly a difficult weekend and week ahead for BA, we do not expect lasting damage to the franchise or long-term forecasts," Deutsche Bank said in a note.
