Boeing's (NYSE:BA) building boom continues.

Thursday, the Seattle planemaker announced that Lufthansa and Swiss International Airlines have placed orders for a total six long-haul 777-300ER airliners, worth a combined $1.9 billion at list prices. (Note: No one ever pays the list price).

In a statement, Swissair noted that it's buying the planes in order to "retain our competitive edge over many of our competitors who are operating aircraft with more than 300 seats on similar routes." Boeing confirms that within this seat-class, "the 777-300ER is a favorite among the world's leading airlines," being "the largest long-range twin-engine commercial airplane in the world, seating up to 386 passengers in a three-class configuration." Airbus's A380 is bigger, of course, but technically, it has four engines.

In related news, reports continue to swirl around Boeing having landed a long-anticipated 200-plane order for its 737 from Irish carrier Ryanair. If correct, such a deal could be worth as much as $14 billion to Boeing -- but, as yet, the reports have not been confirmed by either purported party to the deal.