Bank holidays are prime holiday time, whether that’s a three-day city break or a chance for a longer trip.

However, this weekend a total of 75,000 passengers had their bank holiday escape plans disrupted when they found themselves stranded in two of London’s major airports after British Airways (BA) was hit by a computer systems failure.

This was the second large scale computer failure to hit the UK this month, though unlike the NHS outage this one doesn’t seem to have been caused by a cyber attack.

What happened?

The airline had to cancel all its flights from two of the major London airports: Heathrow, which is also Europe’s busiest airport and Gatwick this weekend after an IT disaster hit its computer systems.

Passengers took to sleeping in the airports whilst awaiting news, whilst others have said their luggage had been lost.

The airline has said it is working to reunite passengers with their luggage, although this could take some time.

What caused the IT disaster?

BA’s chief executive Alex Cruz said a power surge on Saturday morning hit BA’s flight, baggage and communications systems. The crash affected the system used to keep track of passengers, which meant the airline was unable to allow people to board flights.

As well, it also affected the airline’s call centre and website, meaning bookings were also unavailable this weekend.

Apparently, the surge was so strong, it also rendered the company’s backup systems ineffective.

Can you fly with BA now?

BA has confirmed that the airline returned to normal yesterday morning, and plans to run more than 95 percent of flights from Heathrow and Gatwick, though some short-haul flights have been cancelled.

Cruz said:

At Gatwick, we are running a near-full operation, though some flights may be subject to delay. At Heathrow, we plan to fly all our long-haul services – but the knock-on effects of yesterday’s disruption will lead to delays. That is also true for our short-haul operation, and there are some short-haul cancellations.

3 Things That Will Change the World Today

What happens next?

Technically, BA isn’t even 100 percent sure what caused the outage.

Rumours of a potential hack floated around earlier on in the weekend, and the company said it wouldn’t rule out the possibility, however, that rumour has quietened down since.

Cruz has said:

Once the disruption is over, we will carry out an exhaustive investigation into what caused this incident, and take measures to ensure it never happens again.

Read more: British Airways or Indian outsourcer? Who’s to blame for 300,000 stranded passengers

The GMB union has blamed the IT failures on BA itself after it made a number of staff redundant and shifted their work to India last year.

GMB’s national officer for aviation, Mick Rix, told Reuters:

This could all have been avoided. BA in 2016 made hundreds of dedicated and loyal IT staff redundant and outsourced the work to India.

However, Cruz has disputed this claim and said he will not resign over the crisis.

How much has this cost BA?

BA is owned by the Spanish company, International Consolidated Airlines Group (IAG), which also owns other airlines including Iberia and Aer Lingus. IAG’s shares fell four percent in early trading on Tuesday after the outage.

As well, it is thought that BA will have to pay around £100m in terms of compensation, refunds, rebooked flights and additional staffing and related costs.

However, the reputational damage that BA will suffer will run to much more.

Its reputation has been falling for the past few months as a result of cost-cutting measures at the airline.

This disruption will lead to a further drop, in particular as customers may choose not to fly with BA again after this.