A computer glitch caused travel chaos and delays for hundreds of passengers at Heathrow Airport yesterday (Thursday).
A fault with a newly installed British Airways check-in system meant passengers were reportedly turned away from flights.
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The glitch is the second in a matter of weeks: the same check-in system failed in June, causing havoc for passengers at Gatwick and Heathrow airports.
People took to Twitter to air their grievances against the airline.
One frustrated flier shared a picture of queues at Terminal 5, and tweeted: "T5 queues to do bag drop 60 min - ba get with the 21st century."
Another user posted: "Fed up with @BritishAirways what's the point of online check in if it results in just as long a wait? Bag should mean bag drop #FailToServe."
A BA insider told The Sun that holidaymakers face a summer of "chaos" because of the IT problems with some people turned away even if they arrived with plenty of time to board their flights.
British Airways has apologised for the delays but claimed no flights were affected as a result and the issue was now resolved.
A spokesman said: "We are sorry for the disruption to customers' travel plans due to an IT glitch at Heathrow on what was already a very busy morning.
"The issue was resolved as quickly as possible, and all of our flights left as normal.
"Ten million passengers have already used our new check-in system as we introduce it around the world."