51.   But NATO officials and military experts say there are several reasons why the aircraft have been on the sidelines thus far in the Balkan conflict.

52.   But Pike doubted that spy satellites were used for the Unabomber investigation because high-flying aircraft would have been sufficient.

53.   But the aircraft were inexplicably on different frequencies.

54.   But the commission called for reducing duplication of support activities and said aircraft would be a good place to start.

55.   By the end of next year, all commercial aircraft are to be equipped with quieter engines, according to a Federal Aviation Authority mandate.

56.   But witnesses said the aircraft was above the building when the rear rotor sparked and broke off.

57.   Clearly, a carrier-based aircraft is the most expensive way to deliver a bomb to a target.

58.   Congressional foes of the Raptor also believe that the aircraft is overkill.

59.   Defense Departments officials said no American aircraft were in the vicinity at the time of the firings.

60.   Even before the crash, both airlines said the sleek supersonic aircraft would be retired in a decade.