British Airways has cancelled 34 flights from T5 this morning and some short-haul European flights have been cancelled, although passengers will be able to check in luggage.
BA, which has sole use of the £4.3billion new terminal, was forced to suspend baggage check-in following a series of technical problems that wrecked opening day ay T5.
Travellers were left with the option of cancelling or rebooking their flights or flying with just carry-on hand luggage.
Some spent the night at the new terminal.
BA says it plans to operate 80 per cent of flights from T5 today, including all long haul services. It also promised that passengers will be able to check in with hand and hold luggage.
But BA's website hints that disruption may continue this weekend, giving advice as to what to do "if your flight is cancelled" between March 27 and 30.
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BA chief executive Willie Walsh said: "We sincerely apologise to those customers who have suffered disrupted journeys or baggage delays during the first day in Terminal 5.
"We always knew the first day would represent a unique challenge. Whatever short-term difficulties there may be, we have no doubt that it will prove to be a facility of which we, and the whole country, will feel proud."
The airline said a combination of factors were responsible for Thursday's problems.
These included delays at the staff car park and at security, as well as log-in problems for baggage handlers reporting for duty. These factors led to problems processing customers' baggage, it said.
Passengers are advised to check their flight details before leaving for the airport on BA's website or by calling 0800 727 800.
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