51.   Dave Gruel, the activity director, sat at one large terminal in the mission command center, watching for any signs of mechanical failure.

52.   Discussing the current theories on how a catastrophic mechanical failure could have occurred, the investigators expressed strong doubts about all of them,

53.   Early speculation centered on mechanical failure.

54.   Egyptian officials have said that an undetected mechanical failure might have been responsible for the crash.

55.   FBI investigators continue to pursue the possibility that the devastating crash was the result of either a surface-to-air missile attack or a massive mechanical failure.

56.   Federal investigators explored whether mechanical failure, human error or terrorism was the cause.

57.   FDA reviewers also said they were concerned about the potential for mechanical failure and other complications in surgery for implanting the device.

58.   Even with that finding, National Transportation Safety Board officials are unwilling to rule out the possibility of a mechanical failure.

59.   Finding that the crash was caused by mechanical failure would be better than the alternative, but either is bad news for the economy, he said Monday.

60.   Francis warned against ruling out a mechanical failure simply because there has been no case like this one.