Strike action by 12,000 British Airways Cabin Crew members is underway with over 1,000 flights cancelled so far.
The three day stoppage began at midnight last night after Unite's joint leader Tony Woodley accused BA of wanting to "go to war" with the unions. He said he was set a "mission impossible" because of the new offer, which included a four-year pay deal the union maintained would at best freeze wages until 2014.
Heathrow is the worse effected. 1,100 out of 1,950 scheduled flights have been cancelled, only 30% of short haul flights will operate at normal - another four days of strikes are set to begin on 27 March, BA says this weekend's action could disrupt flights into next week as well.
BA said that 65% of passengers would still be able to reach their destination during the first three-day strike.
At Gatwick, all long-haul flights and more than half of short-haul flights are expected to operate as normal.
Short haul at London City airport is also unaffected.
There is still uncertainty at the number of workers who would take part in the strike, or even man picket lines after BA said that any staff who took part in strike action would lose perks, including heavily-discounted travel fares.
BA said it was confident that it could handle 49,000 passengers on each of Saturday and Sunday, compared with around 75,000 on a normal weekend day in March.
BA have called their operation the "biggest ever contingency plan" after chartering rival airlines planes, Unite claim 80 planes are grounded and several charter planes have been scrapped due to technical difficulties.
In a video message on the BA website, chief executive Willie Walsh apologised to passengers for what he said was a "terrible day" for the airline.
However, he said he was confident that a "good service" would be provided.
But, Unite national official Steve Turner said:
"I have seen the 80-plus aircraft that are grounded right now.
British Airways have cancelled an enormous amount of flights and many passengers have realised that given the turmoil they are likely to face today, they are not going to travel and have sought and achieved a refund."
Workers are angry that last November BA reduced the number of crew on long-haul flights and is introducing a two-year pay freeze from 2010.
The airline also proposed new contracts with lower pay for fresh recruits.
Unite says it accepts the need for BA to cut costs, but that it was not consulted on the changes.
BA suffered pre tax losses of £342m for the nine months to the end of December 2009.