GreatBelt is spot on.
Just one detail: if existing crew aplly within three months of entry into force it will be applicable from the date of entry into force. Entry into force will be 20 days after publication, so somewhere in May 2012.
Just to clarify: this is about social security contributions and not about taxes.
Taxes remain payable as per double tax convention between countries of residence of the employer and the employee. (eg: Pilot living in Italy working for FR in Beauvais will pay social security in France his taxes would be Italy and/or Ireland as per tax convention between those countries)