All four boxes of The Ledge, the 103rd floor tourist attraction atop Chicago’s Willis Tower, were closed Thursday morning for what an official said was a routine inspection The move comes hours after cracks appeared in what the official said was a coating designed to prevent scratches on the glass. “Skydeck Chicago is open today while the protective coating is being replaced,” said Brian Rehme, a spokesman for public relations firm FleishmanHillard. “We have temporarily closed the four Ledge boxes for routine inspection we hope to reopen them shortly.” Rehme insisted the structural integrity of The Ledge boxes were sound. More