British Airways has apologised for a “temporary” problem with its check-in systems at some UK airports.
Passengers at Heathrow, Gatwick and London City airports had to be checked in manually and faced long queues and delays.
BA said the fault was resolved at about 09:00 BST and its computerised system was now operating normally.
It comes after a power cut led to hundreds of flights being cancelled over the May bank holiday weekend.
A spokesman for BA said: “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.”
The problems in May resulted in an IT failure and the cancellation of more than 670 flights from Heathrow and Gatwick. BA later said it was caused by an engineer who disconnected a power supply.
Meanwhile, passengers flying from EU airports have been warned they may face long queues over new security checks brought in after recent terror attacks.