Hopes that Heathrow's Terminal 5 could return to a normal schedule have been dashed after further problems with the baggage system.
Airport operator BAA said a software problem meant baggage was having to be sorted manually before being loaded on to flights.
Several flights have been delayed and the departures board is showing that more than a dozen have been cancelled.
A BAA spokeswoman said: "... a software problem has arisen in the baggage system at Terminal 5. This is entirely BAA's responsibility.
"We apologise to BA and all passengers who have been affected, and we assure them that our specialist staff are working hard to resolve the problem and keep disruption to BA's operation to a minimum.
"We know what the problem is. We have a potential solution and we are having to carefully consider how and when we apply this to avoid further problems."
BA had said it hoped to operate a "full flying schedule" on Saturday for the first time since the terminal's opening day debacle last Thursday.
The lower frequency weekend schedule was supposed to give the airport operators some leeway in preparing to run a full weekday service for the first time from Monday.
BA said the terminal was on Thursday running "very well" and there was no fall-off in bookings as a result of the problems, which were expected to cost the airline about £16 million.
But a BA spokeswoman said: "The BAA baggage system in Terminal 5 has suffered another computer problem today, which has caused disruption to British Airways flights. We are urging BAA to resolve these issues as soon as possible."
