41.   But there were signs that U.S. officials have ruled out mechanical failure.

42.   But they have also said there is some circumstantial evidence that points to a mechanical failure, though one official declined to say what that is.

43.   But they have not yet determined if the blast was ignited by a mechanical failure or an explosive device.

44.   But the idea of a mechanical failure still dominates at the safety board, particularly in its Washington offices.

45.   But they said they had no information suggesting that there was a mechanical failure.

46.   Cain said his investigation will focus on mechanical failure and human factors.

47.   Certainly there are many factors that can lead to a plane crash, from weather to mechanical failure to human error.

48.   Despite the new finding, National Transportation Safety Board officials are unwilling to rule out the possibility of a mechanical failure.

49.   Danger could arise if these wires drop to the ground because of weather, accident or mechanical failure, Cablevision said.

50.   Despite occasional mechanical failures and lapses in service, there was only one reported accident involving injuries.