British Airways has apologised after cancelling all short-haul flights from Heathrow Airport on Saturday morning.
The airline said on Saturday afternoon that its IT systems were back working again after technical issues, which it said were not caused by a cyber attack.
BA said there continued to be some cancellations but the majority of flights were now taking off as planned.
Long-haul flights continued to operate with some delays, but all short-haul flights were cancelled until midday.
Passengers travelling from Gatwick or London City Airport also faced some delays due to the issues.
In its Saturday afternoon statement, BA said it was now aiming to complete the day’s flying programme and helping customers whose flights had been cancelled to rebook.
The major outage caused pile-ups of luggage and some customers were stuck on planes after landing at Heathrow.
BA said it knew it had “let customers down” and would do everything it could “to make this up to them”.
“But for now our focus is on getting as many customers and flights away as we can,” the company added.
It is giving customers on cancelled services the option of getting a full refund. Passengers due to fly on short-haul services from Heathrow on Saturday could also choose to rebook for a later date, for free. BA said it would be contacting customers “proactively”.