British Airways cabin crew have mounted picket lines outside airports for the second weekend in a row as another wave of industrial action began in a bitter row over jobs and cost cutting.
Unite said early indications were that its 12,000 members involved in the dispute were strongly supporting the industrial action.
Hundreds of strikers gathered at a football ground close to Heathrow before being taken to several picket lines around the airport.
The airline said it will fly more than 75% of customers booked to travel during the four days of strike action and expects to handle more than 180,000 of the 240,000 people who had planned to travel from March 27-30.
A number of short haul flights left Heathrow this morning and there were arrivals from overseas destinations.
Most long haul services don't leave Heathrow until later in the day.
BA said around 18% of its passengers were re-booked to travel on other carriers, or changed the dates of their BA flights to avoid the strike period.
The two sides continued to clash on the cost of the dispute, with Unite claiming BA will be left with a bill of £100 million because of the current strikes and last week's three day walkout, twice the £7 million a day that BA told the City about earlier this week.
BA reiterated that its "current best estimate" of the cost of the first round of strikes was £7 million a day, and that assessment of the cost of subsequent strikes would only be possible after they had taken place.
Unite officials said that BA had leased fully crewed planes from eight companies, and was again using volunteer pilots and management to stand in for striking cabin crew.
