Board Thread:Theories and Speculation/@comment-35685868-20180605140514/@comment-34640038-20180605144448

It's never particularly stated as to why Hiruzen never used Flying Thunder God while he was alive (or at least why we never saw him use it during his fight with Orochimaru as it would have been the perfect way to escape the barrier he was trapped in if you ask me.) But yes, Hiruzen did in fact know how to use the Flying Thunder God jutsu as evidenced when he was revived along with Hashirama, Tobirama and Minato by Orochimaru and they needed to rush to the battlefield once Madara's chakra presence was felt. If I'm not mistaken, it was also revealed that his technique was the slowest of the group.