Wing Roughness.
The comments about turbulent flow are interesting when put together with the state of the
upper wing tile found in west Texas.
"Normally the shuttle's wings transition from laminar to turbulent flow at 1,200 seconds into re-entry, Gibson said. "On STS-28, on Columbia, that transition happened at 900 seconds -- 300 seconds early. As you might expect, the left wing saw a significantly higher heating environment than the rest of the orbiter."