AVIATION: Jumbo Engine Troubles

While the passenger in a 747 jumbo jet comfortably sips a martini or soaks up the stereo, a rather disconcerting development may be going on inside one of the huge, intricate engines that power the plane. For reasons that still mystify technicians, one or two of the 138 knife-shaped blades in the engine's second-stage turbine may be breaking off in flight and whizzing out the exhaust in showers of tiny metal slivers. The breakoff is so silent that neither passengers nor flight crew notice it, and because it does not lead to fires or loss of power, it usually...