Stephen Labbe, chief of the Applied Aeroscience and Computational Fluid Dynamics branch at Johnson Space Center, said last week that the shuttle experienced an unusual change in forces on its left wing between the shedding of two pieces of observed debris. Despite the presumed damage, he said, the orbiter "executed a perfectly nominal roll reversal," or banking of the wings, about two minutes after the two pieces of debris were shed. Significant damage, he said, can create "locally a very high pressure that is on the lower surface of the wing and starting to push up on the wing."

Labbe and other NASA officials told the board that wind tunnel tests and computational studies simulating various types of damage to the left wing have yet to provide a coherent explanation for all of the forces Columbia experienced before it broke apart. The teams plan to do additional studies that mimic more severe damage than originally postulated, including the loss of multiple leading edge panels rather than just one.

Investigators face a complex task with computational tools they have had to develop as they go. There are no good models, officials said, for what happens when hot gases penetrate a shuttle wing and pass through existing vents or directly attack aluminum spars and ribs.