Holidaymakers travelling through Heathrow and Gatwick were caught in delays and huge queues on Wednesday morning after a British Airways systems crash.
Passengers at Heathrow described “total chaos” after the computers went down at the busy west London airport.
Some travellers awaiting flights from Gatwick Airport also reported problems.
British Airways said on Twitter they were “aware of some issues affecting check in this morning” and apologised to travellers.
It comes after the airline’s IT systems crashed around the world in May, leaving flights from Heathrow and Gatwick airports grounded.
George Edmonds said on Twitter: “All over the place again – computers down at Heathrow. You used to be so good.”
Tim Heptonstall tweeted the carrier and said: “Anything to say about the mess at LGW this morning?”
Colin Parselle, who was travelling to Edinburgh, added: “What have you done to your computers?”
At around 8.45am, a spokeswoman for British Airways told the Standard systems were back up and running after being down for around an hour.
She said: “Customers are being checked in as normal after an earlier problem was resolved. We are sorry for the temporary check in problems which caused some delays for our customers first thing this morning.
“This issue is now resolved and our staff are working flat out to help customers get away on their holidays.”
Today’s problems come after Europe’s biggest association of airlines warned holidaymakers are set to face massive delays at passport control when travelling abroad this summer.
Some passengers have missed their flights or been forced to queue for up to four hours after a new EU regulation means border officials have to carry out extra security checks.
British Airways’ last computer system crash in May, which saw a power outage on its systems around the world, hit passengers for several days, with flights from Gatwick and Heathrow cancelled.
It was thought to be caused by a power supply problem.
Staff at British Airways have a “backlog” in allocating cancellation expenses because of recent disruption.
The airline’s cabin crew are currently in the middle of a two-week strike running until August 15.
Passengers have already been hit with the effects of staff strikes this year. The walkout is over pay gaps between recently-hired mixed fleet crew and ordinary cabin crew.
Unite the union said half of the new recruits have been forced to take a second job to earn enough for living.
A Heathrow spokesperson said on Wednesday: “Due to issues experienced earlier with the British Airways check-in system, some passengers experienced minor delays in Terminal 5.
“We apologise for this experience and can confirm the issue has now been resolved.”