Shuttle wing breach had happened before

Superheated gases breached the left wing of shuttle Atlantis during its fiery return to earth in hauntingly similar fashion to the demise of Columbia nearly three years later, according to internal NASA documents.

Unlike Columbia, Atlantis suffered no irreparable damage during the May 2000 episode and, after repairs, returned to flight just four months later. NASA ordered fleetwide changes in how employees install protective wing panels and sealant materials.

Engineers found the damage on Atlantis while investigating the mystery of a partially melted insulating tile. Removing two protective wing panels nearby and peering inside the wing structure, they determined the dislodged seal had created "a substantial flow path," according to NASA's internal reports. The gap measured just over one-quarter inch, about the width of a paperclip or a No. 2 pencil.

The protective panels, insulators and other hardware inside the left wing "shows various signs of overheating," NASA reported. Photographs showed charred and scorched components, including parts made from titanium and inconel, two of the most heat-resistant materials on the shuttle. Titanium melts about 3,000 degrees; inconel melts about 2,550 degrees.

Investigators examining Columbia's breakup remain uncertain over the size of the gap that permitted hot gases to penetrate that shuttle's wing. But they believe it was as small as a one-inch slit running vertically up the wing for nearly 30 inches. In a test Monday, a chunk of foam blew open a dramatic 16-inch hole in parts of a mock-up of a shuttle wing.