41.   But because the planes cannot be delivered for a few years, traffic growth often trails off as the new planes hit the market.

42.   But by that time, aviation experts determined it would be cheaper to build new planes than retrofit existing ones.

43.   But Britain, which has always contended that it cannot wait more than a decade for a new plane, has always been a question mark.

44.   But documents show airlines are finding careless and shoddy workmanship in those new planes.

45.   But engine makers have already submitted bids to Boeing to supply the monster engines that will be needed to power the huge new plane.

46.   But even Coupland was startled when Alex Trebek, that unacknowledged legislator of cultural immortality, took the linkage to a whole new plane two months ago.

47.   But before the Pentagon determines which prototype has the right stuff, it plans to ensure that the new plane will have the right price.

48.   But orders for new planes, especially from China and Saudi Arabia, have been slow to materialize.

49.   But paying for new planes will not be easy.

50.   But the new Boeing planes face significant challenges.