Crab, DML and Bing; Wrong disaster. I was referring to Columbia 2003 (foam insulation punctured leading edge) not Challenger 1986 (o ring burn through) . As far as I know PP played no part in the 1986 accident. In 2003 NASA detected the foam strike on launch and, with the Orbiter still in space, contracted Boeing to analyse the risk. They presented their findings in the world’s worst pp slide( Google columbia, powerpoint) . Boeing thought they were telling NASA that there was a significant risk. NASA took away that there was little risk.