As the British Airways strike gets under way, hundreds of cabin crew join picket lines while the airline claims its plan to keep passengers flying is "off to a good start".
BA cabin crew started their three-day walkout at midnight after talks between the airline and the union Unite broke down.
With 1,100 flights cancelled, the industrial action is upsetting travel plans for thousands of air passengers this weekend.
BAsaid it had put in place its biggest ever contingency plan to try to get 65% passengers to their destinations.
It is operating all flights to and from London City airport and all long-haul flights to and from Gatwick airport in West Sussex.
The airline plans to run 50% of its short-haul Gatwick services, about 60% of its Heathrow long-haul services and about 30% of its Heathrow short-haul flights.
I am satisfied that our contingency plans are robust. We are very confident that we will continue to fly our customers in comfort.
BA's Willie Walsh
A spokeswoman said: "At Heathrow and Gatwick we have got off to a good start. London City is operating as normal.
"Cabin crew are reporting as normal at Gatwick and the numbers reporting at Heathrow are above the levels we need to operate our published schedule."
BA has arranged with more than 60 other airlines to take its customers on their flights on the first strike days.
While some passengers whose flights have been cancelled are travelling on other carriers, others have arranged to fly with BA at a later date and some have opted to get a refund.
Sky sources said the carrier has estimated that more than 100,000 passengers have cancelled their tickets since the strike dates were announced at a cost to the airline of £27m.
Uniteclaimed its 12,000 members were solidly supporting the walkout, called in a bitter dispute over cost cutting.
The union is holding a rally at Bedfont Football Club and picket lines have been mounted at several entrances to Heathrow.
One flight attendant at Heathrow, speaking anonymously, said: "The morale here is fantastic and the public support is tremendous with everyone hooting their horns.
"We have seen only one BA short-haul aircraft take-off in the last 40 minutes. (Willie) Walsh (BA chief executive) seems to think 64% of passengers will be flying but we think that's very optimistic of him."
Sky News reporter Enda Brady said Heathrow was "extremely quiet" as the strike got under way.
"People seem happy enough to be flying but looking around there are hardly any passengers - it's the quietest I've ever seen Heathrow," he said.
"Looking at the flight departure board, it is surprising how many flights are by other operators."
BA's Willie Walsh
BA made record losses of £401m in the 2008/9 financial year and a record loss of £292m for the six months to the end of last September.
A four-day stoppage is also set to start on March 27, with further action expected from mid-April unless the deadlock is broken.
Unite's deputy general secretary Len McCluskey told Sky News he was disappointed that negotiations had failed and accused BA of a "heavy handed approach" with the union.
"It's obviously a sad day, no one wanted to get to this position, certainly not our cabin crew, but the response has been magnificent.
"We've said all along to BA that this can only be resolved through negotiation, not through intimidation, confrontation or litigation."