A computer software failure prevented thousands of passengers at Heathrow's Terminal 4 from checking luggage in on Tuesday and Wednesday (19 and 20 February).
Economy long-haul passengers were only able to take two pieces of hand luggage on board after the BAA software failed.
British Airways, the terminal's main carrier, told customers they were likely to face severe delays and many were not able to travel as planned. The problems also affected transfer passengers leaving from Terminal 4.
A spokesman for British Airways said, "It had quite a significant impact, but thankfully the system is back up and running. Our biggest problem was letting people know what was going on." The airline said affected passengers can either be re-booked on another flight or get a refund.
BAA said full service was restored by Thursday (21 February).
The company said in a statement on Wednesday, "The performance of the Terminal 4 baggage system has today been significantly reduced by an ongoing software problem.
"Whilst every effort was made to rectify the problem overnight and despite contingency plans put in place this morning, British Airways passengers travelling to long haul destinations from Terminal 4 today have had their travel plans seriously impacted upon.
"BAA would like to sincerely apologise to these British Airways passengers who have had their travel plans disrupted."