Unlike AS2 developers can’t use Key.isDown in AS3. But, while you are making a game like racing or people moving you must work with two/three key press which can’t be achieved without Key.isDown.
I was facing the same problem when one of my dev Zeeshan was working with car racing game. So, went for some Googling and found this http://www.kirupa.com/forum/showthread.php?p=2098269 Thanks Guru for the beautiful class.