Thousands of travellers have been stranded after British Airways' online check-in system crashed due to an IT glitch.
The airline apologised to customers for the disruption and said its technical team was working to resolve the problem.
"We are experiencing some systems problems this morning which are affecting check-in and flight departures," it said.
"This is affecting other systems as well."
Just over a year ago, BA was forced to cancel flights at Heathrow, due to problems with a supplier's IT system.

India arrests Kashmir resident over deadly Delhi car blast
Netanyahu faces far-right backlash after US-backed statement on Palestinian state
Ukraine seeks exchange of 1,200 prisoners with Russia
Refugees in UK to face 20-year wait to settle permanently
Blast at police station in Indian Kashmir kills nine, injures 27
