slats11, consider that at least on some planes the seat bottom cushions are designed for flotation. Way back in the old threat it was pretty much settled that the bodies sank to an equilibrium level. Then as they bloated they rose if they managed to float out of loosely fastened seat belts. One person claimed that bodies, especially broken bodies, could work their way out of even fairly tight seat belts. He claimed sufficient fresh water experience, if I recall, to make that believable.
That has me wondering "where are the cushions that should have floated?"