1.   At worst, however, undetected cracks could cause simultaneous rupture of several tubes, leading to the release of radioactivity into the environment.

2.   Managers say the pump problems were caused by cracks in the steel and that a different type of pump will be used for future tests.

3.   The cracks could cause the disks to fly apart and prompt engine failure, the FAA said.

4.   The cracks could cause the discs to fly apart and prompt engine failure, the FAA said.

5.   The most recent postponement was caused by cracks found in June on the left wing during ground tests.