From the Recent Atlantic Monthly, "Columbia's Last Flight: The inside story of the investigation—and the catastrophe it laid bare" by William Langewiesche (v292i4 Nov 2003). This doesn't appear to be onlline, but is well worth seeking out. Langewiesche is also the author of the truly excellent series "American ground: unbuilding the World Trade Center" from the July-August, September and October issues of 2002. It was also published as a book.