A further two walkouts are planned by the Unite union if the long-running dispute is not resolved — an increasingly likely eventuality after weekend talks broke down in acrimony.
BA said it plans to carry 70 percent of booked passengers over the strike period, with flight schedules at Gatwick and London City airports unaffected by the walkout.
But services at Heathrow were hit — adding to travel misery for passengers just weeks after the closure of European airspace because of the Icelandic volcanic ash cloud and a seven-day BA cabin crew strike in March.
Most of the anger from affected passengers was again directed at the striking workers, some of whom gathered on an open-top double-decker bus near Heathrow's perimeter fence, waving banners reading "Brutish Airways." On another picket line at a nearby Underground station, workers held placards with the message: "We had no choice." That sentiment wasn't welcomed by Maureen Lonergan, 66, who had to fly to London from Manchester a day early to make a connecting flight to Venice, forcing her to pay for an extra night's accommodation in the British capital.
"I think the strikers are greedy. We've heard they get paid more than other airline staff anyway," Lonergan said.
"The way the economy is, they should be grateful they have jobs in the first place. It puts you off flying BA." The airline has scrambled to operate as many flights as possible — using non-striking cabin crews, staff seconded from elsewhere in the company after undergoing training, leasing aircraft complete with crew and transferring passengers to competitor airlines.
It planned to operate 60 percent of long-haul flights and 50 percent of short-haul flights from its Heathrow base.
Canceled flights included services to New York, Amsterdam, Frankfurt, Rome, Vienna and Prague.
The walkout in the increasingly bitter feud follows the failure of weekend talks between the Unite union, which represents around 90 percent of BA's 12,000 cabin crew staff, and the airline.
British Airways said it has accepted an invitation for more negotiations, and says it believes the union will also accept.
While the two sides are close to agreement on many issues, mistrust and bitterness have made a deal elusive. Unite joint general secretary Tony Woodley accused BA of having a "petty, vindictive" attitude after it revoked strikers' low-cost travel — a cherished cabin-crew perk — and took disciplinary action against striking workers.
British Airways said it had already offered to reinstate travel concessions to cabin crew — which see them pay just 10 percent of normal fares to commute to work from across Britain or continental Europe — once all elements of its offer were implemented, but it accused Woodley and the union of reopening issues which had been settled.
BA Chief Executive Willie Walsh also expressed anger that one of the union's leaders, Derek Simpson, had been posting updates on Saturday's talks on Twitter.
The strikes would bring more financial hardship to BA, which posted a record annual loss of 425 million pounds ($611 million) on Friday.
The airline has been struggling to have a clear run since cabin crews walked out twice in March for a total of seven days. More flights were canceled earlier this month during the sporadic closure of European airspace because of the volcanic ash and the airline ran a curtailed service last week when cabin crews had been due to strike — the walkout was delayed by a legal challenge from BA.
The airline's combative CEO has repeatedly warned that contentious changes to work practices, including fewer staff on long-haul flights and a yearlong pay freeze, are necessary for BA to survive.
The company has been hit hard by the financial downturn because of its heavy reliance on premium fare passengers on the trans-Atlantic route. As many leisure and business travelers seek lower cost options, there are fears that its core business will never fully recover.
