I don't think the larger fan blades did leave the cowling. Based on the couple images I saw of the failed engines (e.g. [0]), the smaller, hotter blades farther

I don't think the larger fan blades did leave the cowling. Based on the couple images I saw of the failed engines (e.g. [0]), the smaller, hotter blades farther aft [1] were the ones that punctured the cowling. These have less protection because the wing protects the passengers from flying debris whereas the compression and intake fans stick out far enough to require separate cowling for passenger protection. [0] http://www.newstalkzb.co.nz/img_up/QantasEngine250.jpg http://www.newstalkzb.co.nz/img_up/QantasEngine250.jpg [1] http://en.wikipedia.org/wiki/File:Jet_engine.svg http://en.wikipedia.org/wiki/File:Jet_engine.svg