1.   And the ignition source apparently was something which had smoldered for a few days.

2.   As a result, the investigation has zeroed in on possible ignition sources.

3.   At the time, safety board officials said they had ruled out those pumps as possible ignition sources.

4.   Because of that, The Boeing Co. insisted Tuesday that no ignition sources exist on its airplane center fuel tank systems, despite two unexplained aircraft explosions.

5.   Before the crash, the FAA believed that safety could be assured by preventing any ignition source in the tank.

6.   It is not rational to believe that we can predict all possible ignition sources.

7.   Both FAA proposals are intended to eliminate ignition sources around the center fuel tank.

8.   But every effort to find tangible evidence of an ignition source has failed.

9.   But the FAA has said more research is needed to determine the possible ignition source.

10.   But then, as now, nobody could find an ignition source.