DUBLIN (Reuters) - Ryanair announced a US$15.6 billion (S$19.5 billion) order for 175 passenger jets from Boeing on Tuesday in a deal that will allow the Irish airline to consolidate its position as Europe's dominant low-cost carrier.

The order for the 738NGs keeps Ryanair as one of the few remaining all-Boeing airlines, after Lion Air of Indonesia switched to rival planemaker Airbus on Monday in a US$24 billion mega-order.

The deal will see Ryanair increase its fleet to around 400 planes from 300 at present, as 75 planes are retired.

Reuters reported exclusively in late January that Ryanair was closing on a deal for at least 150 current-generation 737NG passenger jets to be completed within weeks. Ryanair denied the story at the time.

The order for current-generation 737 aircraft delivers a timely boost to Boeing, which last week won US approval for test flights for its grounded 787 Dreamliner. It will also provide it with a smooth transition to its new 737 Max aircraft, scheduled to enter service in 2017.

The industry benchmark 737-800 model is worth US$89.1 million at list prices, but large orders attract steep discounts and industry appraisers value the plane closer to US$40 million.