21.   A Boeing spokeswoman suggested, however, that if there was no evidence of mechanical failure, then perhaps there was none.

22.   A finding of mechanical failure would instantly spell lawsuits.

23.   A separate investigation by the National Transportation Safety Board into whether mechanical failure caused the explosion will continue, officials said.

24.   A simple mechanical failure, a random spark that ignited jet fuel in a one-in-a-million episode?

25.   A separate investigation by the National Transportation Safety Board into whether mechanical failure caused the explosion will continue.

26.   Abiomed has kept the artificial heart beating in the laboratory for more than a year without mechanical failure, Lederman said.

27.   Airplane manufacturers often conclude that their planes could recover from a given mechanical failure in flight because their design engineers assume pilots would take corrective actions.

28.   All along, Eitan Sobel had held out hope for a mechanical failure.

29.   But by leaning toward a terrorism theory, critics say, the FBI came into conflict with safety board investigators who favored a theory of mechanical failure.

30.   But if no cause is found, mechanical failure would probably become the explanation by default.