British Airways pilots have launched a 48-hour strike in a dispute over pay.
Members of the British Airline Pilots Association (Balpa) are taking their first ever industrial action against the airline, grounding hundreds of flights.
BA has offered a pay rise of 11.5% over three years but Balpa says its members wanted a bigger share of the company’s profits.
The airline said its offer would take the pay of some captains to more than £200,000.
The airline has spent weeks offering refunds to passengers or the option to re-book to another date of travel or an alternative airline.
The airline operates up to 850 flights a day, with most expected to be cancelled, affecting up to 145,000 passengers.
Heathrow Airport will be worst affected as it is the busiest hub for BA.
Passengers whose flight have been cancelled have been urged not to travel to the airport.
Further strike action is also planned for September 27, after BA lost a Court of Appeal bid to stop the pilots walking out.
BA said it was “extremely sorry” for the cancellations and told customers affected they can expect a full refund.
Passengers should have been informed via email whether their flight has been definitely cancelled.
Options on what to do next can also be found by logging into the BA website and visiting the Manage My Booking page.
Customers with flights on Monday and Tuesday can rebook cancelled trips or claim a refund on the British Airways website, the airline said.
Balpa has argued pilots should be given a greater share of the airline's “massive profits”, in part for their sacrifices and efforts to help BA recover from recent struggles.
BA defended the offer as “fair” and said it had already been endorsed by the Unite and GMB trade unions to the almost 90% of BA staff they represent.
BA said in a statement: “We understand the frustration and disruption Balpa’s strike action has caused our customers.
"After many months of trying to resolve the pay dispute, we are extremely sorry that it has come to this.
“We remain ready and willing to return to talks with Balpa.
“Unfortunately, with no detail from Balpa on which pilots would strike, we had no way of predicting how many would come to work or which aircraft they are qualified to fly, so we had no option but to cancel nearly 100% of our flights.”
Both sides have said they want to resume talks, but there is little or no sign of the deadlock being broken.
In a statement, Balpa said: "Our members’ resolve is very strong and they remain very angry with BA, but they also want to leave no stone unturned in trying to find a resolution to their dispute."
"British Airways must now put the needs of its staff and passengers first and accept that its pilots will not be bullied or fobbed off.
“The company’s leaders, who themselves are paid huge salaries and have generous benefits packages, won’t listen, are refusing to negotiate and are putting profits before the needs of passengers and staff.
“This strike will have cost the company considerably more than the investment needed to settle this dispute.
“It is time to get back to the negotiating table and put together a serious offer that will end this dispute.”
Balpa said the strike will cost BA £40 million a day, claiming the dispute could be settled for £5 million.
- What are your rights if your flight has been cancelled?
Airlines are bound by EU law to pay passengers if a flight is cancelled less than a fortnight before departure - with the exception of "extraordinary circumstance" - or delayed by more than three hours (up to £530).
Strike action doesn't fall into the category of "extraordinary circumstance", so passengers can apply to airlines for compensation unless they accept a refund.
Travel insurance does not normally cover strike action by airline staff.
BA has said all passengers affected will get a full refund, that they can re-book their flights on the company's website, or re-book with an alternative airline.