British Airways faces a compensation bill in the region of £100m ($128.6m) after a worldwide IT outage led to 75,000 passengers being stranded over the bank holiday weekend.

All of the airline flights at London Heathrow and Gatwick were left grounded, after the computer system used by BA suffered a "major" global failure on Saturday (27 May). By late afternoon on the same day, the carrier's computer systems, app and website had all gone into shut down, leading to chaotic scenes at both airports as passengers sought explanations.

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BA chief executive Alex Cruz blamed the IT failure on a power surge and promised that the airline would compensate the customers whose travel plans were disrupted over the weekend.

In a statement released on Tuesday, BA said its IT systems were "back up and running" and that flights will be operating as normal at Heathrow and Gatwick, but warned that "it may take some time" for baggage to be reunited with their correct owners.

"Although we have already flown many bags to the correct airport, there is still some work to do and we know there are still significant numbers of customers who are yet to receive their luggage," it said.

"Given the nature of global travel, it may take some time to complete the process of reuniting bags with their owners around the world.

"We are very sorry for the frustration this situation is causing at a very busy time of year for holidays."

So what can disgruntled passengers do to claim compensation and how much are they entitled to receive?

What the law says

BA will have to pay out compensation under the EU Regulation 261/2004 that requires payment for flights delayed by three hours at final destination. The situation for the airline is made worse by the fact that the events of the weekend were not an extraordinary circumstance - such extreme weather or anything outside its control.

"This is not like an ash cloud or traffic controllers' strike that can't be predicted," said James Walker, chief executive of Resolver, a free flights compensation claim site.

"The computer system breaking down is within its control. BA is going to have to pay out and it looks like its costs will be north of £100m."

What should have BA provided to passengers?

In the event of a flight being delayed by two hours or more, airlines are ought to provide a number of items for free, including:

  • Food and drinks - in reasonable amount to the waiting time (Only paid by an airline if flying with a EU airline or if departing from an EU airport).
  • Overnight accommodation if necessary. (Only paid by an airline if flying with a EU airline or if departing from an EU airport).
  • Two phone calls, emails or fax messages.
  • Travel to and from the airport and accommodation.

Passengers flying outside the EU are not entitled to food and drinks, but the airline must either issue a refund or try and issue an alternative ticket.

What happens for longer delays?

Passengers delayed by five hours or more regardless of flight distance can demand reimbursement of their full ticket price within seven days, regardless of flight distance.

What happens for cancelled flights?

According to BA's website, passengers whose flight is cancelled, have the choice of either:

  • Re-routing, under comparable transport conditions, to the final destination of the ticket presented at check-in at the earliest opportunity or at a later date at the passenger's convenience, subject to availability; or
  • A refund payable to the person who purchased the ticket. This applies to the part or parts of the journey not flown.

If the flight is delayed for five hours or more, the purchaser of the ticket is entitled to a refund for the part or parts of the journey not flown.

How much compensation are passengers entitled to?

The amount payable depends on the distance of the flight and the length of the delay and compensation is in euros.

Under the rules set by EU Regulation 261/2004, the levels of compensation are:

  • €250 for flights of up to 1,500km.
  • €400 for flights within the EU of more than 1,500km, and for all other flights between 1,500km and 3,500km.
  • €600 for all other flights.

However, the amounts listened above are halved by 50%, if the airline is able to offer an alternative route to the same destination on flights whose scheduled arrival time does not exceed the original arrival time by:

  • Two hours for flights of up to 1,500km.
  • Three hours for all flights within the EU of more than 1,500km, and for all other flights between 1,500km and 3,500km.
  • Four hours for all other flights.
LON:IAG