On 2/23/2007 6:21 PM, Roy Smith wrote the following:

If you've already told the controller you have an emergency, squawking 7700
doesn't add anything to the situation. The 7700 stuff is for when you're
out of radio contact.

Au contraire. With a 7700 squawk then if the emergency situation wasn't
mentioned in the handoff (which it possibly wasn't) then the next controller
would still have known something was seriously wrong.

(Now possibly if AA had squawked 7700 he would have been asked to switch off
that code at some point, but we don't even know from the video whether he tried it.)