British Airways is expected to reveal a £600 million slide into the red as the airline faces a fresh wave of strikes.
The drop for the year to March - the worst since BA was privatised in 1987 - brings total losses in the past two years to £1 billion, following a £401 million reverse in 2009.
The latest results include an estimated £40 million to £45 million hit from the first round of strikes in March and come as the cabin crew union celebrated a dramatic court victory which cleared the way for another 15 days of industrial action.
On Thursday, Unite won an appeal in London against an injunction which blocked a planned five-day walkout this week and later confirmed strikes would start next Monday.
Cabin crew will take action for five days, followed by further five-day stoppages from May 30-June 3 and from June 5-9, threatening travel chaos for tens of thousands of passengers.
Shares in BA were trading almost 4% lower after Unite won its appeal and the new strikes could cost the firm another £100 million in the current financial year, with Iceland's volcanic ash cloud adding to its woes.
BA said it was "disappointed" with the Court of Appeal's ruling but insisted it would implement its contingency plans to keep aircraft flying.
It intends to operate a full schedule at Gatwick and London City Airport, about 60% of long-haul flights at Heathrow and about 50% of the west London airport's short-haul programme during the strikes.
Chief executive Willie Walsh said: "I fully respect the decision, however I make no apologies for going to the court in the first place. I've made it clear to everybody that I will explore every avenue. I will look at every option that's available to us to try and protect our customers from the actions of this trade union."
He urged Unite's leaders to "reflect on the progress" that was made and to "look for the opportunity" to end the dispute, but Unite's joint general secretary Derek Simpson said there had to be an honourable settlement, stressing that the two outstanding issues of travel concessions and staff suspensions had to be resolved.