Yes. You can even fleet in the opposite direction to the way in which you were falling back - the falling back "chacha". But most people agree that you must move within the 'fallback corridor' as defined in the rules, so no fleeting sideways.
http://www.dakkadakka.com/Default.aspx?tabid=93&view=topic&forumid=15&postid=72624
BTW, the "search this forum" window at the top right is extremely useful. I typed in "fleet falling back" and found that thread straight away