Original quote by tdracer DevX - again, speaking Boeing here, but aside from some of the very early jet aircraft (which had flight operable T/R - I'm thinking maybe the DC-8 had those)
Indeed, the original DC-8s were capable of reversing thrust in the air, but only on the two inboard engines, the CFM56 re-engined aircraft did not. It was used for rapid descent. Some of the pilots would announce ahead of time they were going to use in-flight thrust reversing as the resulting vibrations in the cabin were extremely noticeable. Interestingly, I read the Concorde also had this capability as did the HS Trident.