British Airways (BA) has apologised after IT issues caused dozens of flights in and out of Heathrow Airport to be cancelled.
A number of short-haul flights were cancelled on Wednesday evening and Thursday morning after an incident involving a "supplier IT system".
It added to earlier disruptions on Wednesday caused by a fire alert at Heathrow's air traffic control tower.
BA said the IT issue had been resolved but knock-on delays remained.
Some passengers said they had been delayed by almost 15 hours.
BA said: "An issue with a supplier IT system was resolved overnight. We are doing everything we can to keep any knock on disruption to our services to a minimum.
"We have apologised to our customers for the delay to their travel plans."
The carrier, owned by IAG, suffered a large computer system failure in May 2017, caused by a power supply issue near Heathrow, which stranded 75,000 customers over a busy holiday weekend.
Its chief executive said at the time it would take steps to ensure such an incident never happened again
Customers have tweeted their frustration at the recent disruption.
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