Thousands of British Airways passengers are facing "total chaos" due to a "worldwide" IT failure that has grounded planes because it is unsafe to take off.
Frustrated holidaymakers - including parents with babies - were stuck on board planes for hours due to severe disruption at airports across the UK, including Heathrow, Gatwick and Glasgow, and in Italy.
British Airways has cancelled 81 flights due to operate to or from Heathrow while 10 Gatwick flights were cancelled.
More than 200 other flights were delayed, with some more than five hours behind schedule.
One passenger stuck on a flight from Newcastle for two hours said the pilot told those on board that it was a "global" failure.
Holidaymakers told how their getaways were thrown in doubt and some passengers became so frustrated they just walked off planes and gave up.
BA confirmed it was experiencing "systems problems" which were affecting the check-in process - including its app - and delaying flight departures.
The airline was using back-up and manual systems to try and cope with the failure.
Passengers said they were told the system used to generate load sheets for flights had failed. The same system failed and caused travel disruption for thousands of BA customers last month.
A British Airways spokesperson said: "We are working as quickly as possible to resolve a systems issue which has resulted in some short-haul cancellations and delays from London airports.
"A number of flights continue to operate but we are advising customers to check ba.com for the latest flight information before coming to the airport.
"We are offering customers booked on short-haul services departing from Heathrow, Gatwick and London City today, the opportunity to rebook to another day.
"We are encouraging customers to check ba.com for the latest flight information, and to allow additional time at the airport."