Strike-hit British Airways has said the airline had got off to a "good start" as its plans to cope with a mass walkout of cabin crew staff swung into action.
But the three-day strike by an estimated 12,000 BA cabin crew - their first in 13 years - was expected to cause disruption for thousands of passengers.
A spokeswoman for BA said that the airline had "got off to a good start" as it implemented contingency plans at UK hub airports.
The Unite union, in contrast, claimed a number of planes were starting to stack up at airports as a result of the strike. The union claimed there were 85 parked planes at Heathrow, 20 at Cardiff and 20 in Shannon.
Unite said early indications were that its 12,000 members were solidly supporting the three-day walkout, which started at midnight in a bitter dispute over cost cutting.
Picket lines were mounted at airports including Heathrow, and Unite said that no buses which normally transport crew to work, had crossed picket lines.
A BA spokeswoman said: "We aim to fly as many customers as we can this weekend. At Heathrow and Gatwick we have got off to a good start. London City is operating as normal.
"Cabin crew are reporting as normal at Gatwick and the numbers reporting at Heathrow are above the levels we need to operate our published schedule. This is the biggest contingency plan we have ever launched."
BA also confirmed that a number of long-haul flights were running without passengers so planes could be in the right place when the strike ends. BA is planning to operate all long-haul flights to and from Gatwick plus around half of short-haul flights, while all flights to and from London City Airport are expected to fly as scheduled.
The company said it was confident of handling as many as 49,000 passengers on Saturday and the same number on Sunday, which compares with a figure of around 75,000 for a normal weekend day in March.
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