Ryanair pilots are holding their second 24-hour strike in just over a week.
The 100 Irish-based staff already walked off the job last Thursday in their row over seniority.
The pilots, who are members of the Irish Airline Pilots Association, are in dispute with the company over base transfers, leave and seniority issues.
Talks between their union and Ryanair management broke down earlier this week. With no breakthrough in sight, more strike action is scheduled for next Tuesday.
Last night Ryanair called on Forsa to call off next week's day of action but a 7 o'clock deadline came and went without any response.
24 flights out of Dublin today have been cancelled to the UK. The company says it is cancelling flights on routes with higher volumes so people can more easily transfer to other services.