British Airways cabin crew will on Monday take their 20th day of strike action, with no sign of a breakthrough in their bitter dispute with the airline.
Members of Unite will remain on strike until Wednesday, but the union is threatening to hold a fresh ballot if the deadlocked row is not resolved soon, which could disrupt flights in the busy summer months.
BA said more crew than expected had turned up for work since the start of the latest five-day walkout on Saturday at Heathrow airport, meaning it could operate additional flights.
Strike pay has been increased from £30 a day to £45 for the current strike period, and Unite is considering offering interest-free loans of £1,000 for hardship cases.
The cost of the industrial action to BA will be well over £150 million by the time the current strikes end on Wednesday.
The impact of the dispute was revealed this week when the airline announced a 14.2% dip in passenger numbers last month.
A BA spokesman said: "Our global operations went very well last week and we have got off to another good start at the beginning of this strike period. The numbers of crew reporting for work at Heathrow has been higher than we expected and as a result we have been able to operate additional flights to Los Angeles, Washington, Mexico City and Phoenix.
"These flights are in addition to the larger schedule previously announced at Heathrow for this period of strike action. We will continue to operate 100% of our schedule at Gatwick and London City airports and our cabin crew at Gatwick continue to ignore Unite's strike calls and work as normal."
BA is aiming to operate around 80% of long-haul flights from Heathrow despite the strikes, up from 70% and 60% in the past two strike periods, and 60% of short-haul flights, up from 55% and 50%.
Talks between Unite's joint leader Tony Woodley and BA's chief executive Willie Walsh under the auspices of the conciliation service Acas ended without agreement last week, with little sign of any progress. An agreement in principle has been struck over cost-cutting, the original cause of the dispute, but the removal of travel concessions from strikers is now blocking a deal.