Aer Lingus is extending its relationship with United Airlines on some long-haul services between Europe and the US, and has held out the prospect of forming a new joint venture company with the US airline.

The two airlines will launch a daily service between Washington and Madrid from March 2010. Additional routes may be made available from next year for services to begin in Summer 2011.

Aer Lingus said that further expansion and development of the partnership's activities will be jointly assessed and agreed by the partners and may develop into a 'broader and deeper' joint venture, in which Aer Lingus would have a controlling interest.

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Aer Lingus and United Airlines launched code services between Ireland and the US in October 2008.

The airlines expect the new partnership to report a 'marginal' level of profit in the first year. Aer Lingus will provide three planes, which will be leased to the partnership, and the planes will have the Aer Lingus logo on the outside with joint branding inside.

Recruitment for the new partnership will be in the US. Tickets will be on sale in around six weeks.

'We are very excited by the potential of the partnership and believe that the unique combination of two leading transatlantic airlines can drive significant value for the shareholders of both companies,' commented Aer Lingus CEO Dermot Mannion.

In Dublin, Aer Lingus shares closed down four cent at €1.35, but Ryanair gained 11 cent to €3.03.