Thousands of British Airways passengers could be entitled to compensation after a global IT failure caused mass disruption over the weekend, which was a bank holiday in the UK.
Here are the regulations on payouts:
Stranded holidaymakers spent the night on yoga mats on airport floors as disruption from the British Airways system failure continued into a second day.
— Plane Finder (@planefinder) May 27, 2017
BA grounded all planes from Gatwick and Heathrow on Saturday, causing chaos for thousands.
The disruption continued into Sunday, with dozens of Heathrow services cancelled and passengers warned not to go to the airport without rebooking or checking their flight status.
Some shops at the airport had run out of food and many people slept on the floor on mats and blankets.
The problem has been caused by a worldwide systems failure, which BA said is believed to have been caused by a power supply issue.
Passengers lucky enough to be aboard one of the few flights taking off on Saturday later found their hold luggage had not made it onto the plane with them.
Terry Page, 28, from London, flew from Heathrow to Fort Worth, Texas, where he and "about 50" others were told they would have to wait until Monday before being reunited with their bags, he said.
BA chief executive Alex Cruz said the airline was "extremely sorry" for the "huge inconvenience" suffered by customers.
BA said it is aiming to operate a "near normal schedule" at Gatwick and the "majority of services" from Heathrow.
There were dozens of cancellations at Heathrow on Sunday morning and delays of around 30 minutes to their flights from Gatwick.
The airline was unable to say how many flights would be cancelled or how long the disruption is likely to continue for.
A spokesman said: "Our focus is on updating customers and doing what we can to get them to their destinations as quickly as possible."
Experts predict the knock-on effect could continue for several days and BA is facing huge compensation costs.
The glitch is believed to have been caused by a "power supply issue" and there is no evidence of a cyber attack, the airline said.
There were issues with its online check-in systems in September and July last year, causing severe delays for passengers.
Mr Cruz said in a statement on Sunday afternoon that many of the systems are back up but the knock-on effect is continuing.
He warned passengers that the BA Heathrow terminals were "very congested" and that people would not be let into Terminal 5 until 90 minutes before the scheduled departure time of their flights.
Anyone who had their plane cancelled can rebook until the end of November or have a full refund, he added.
He apologised again for the "horrible time" and "very trying experiences" customers have been through.