A company controlled by Mr David Bonderman, who is chairman of Ryanair, is to sell its shareholding in Continental Airlines as part of a deal with another US airline. Mr Bonderman holds almost 16 per cent of Ryanair.

The deal will involve the fourth and fifth largest US carriers, Northwest Airlines and Continental Airlines, forging a global alliance. It will link their route and ticketing systems around the world. Continental Airlines is to start flying Dublin-Newark and Shannon-Newark as part of its summer schedule and is expected to provide stiff competition for Aer Lingus on the transatlantic route. The alliance, to take effect later this year, will also connect the frequent flyer programmes of the two companies and will enable co-operation between Continental and KLM Royal Dutch Airlines, Northwest's trans-Atlantic partner.

Ironically, Aer Lingus already has an alliance with KLM. An Aer Lingus spokesman said last night that it was too early to tell if this would be affected by the Continental alliance.

Northwest in addition said it had reached an agreement to acquire the Continental common stock held by Air Partners, Mr Bonderman's company which represents 13.8 per cent of Continental's capital but around 52 per cent of the voting rights.

Mr Bonderman has been credited with helping to turn Continental around. His company bought into Continental in 1993 through a $64.3 million investment. He led the $450 million refinancing of Continental. Meanwhile, an Aer Lingus spokesman refused to confirm or denyreports yesterday that it was in negotiations with Swissair, with a view to forming a strategic alliance. Aer Lingus has been mandated by the Government to produce a report on possible alliance partners.