Fate of the 4th 9/11 plane

I just read an article on AOL news that gave compelling evidence from the 9/11 hearings.

"Vice President Dick Cheney eventually issued an order to shoot down hijacked planes, but military pilots did not receive it until the last of the four planes - United Airlines Flight 93 - crashed in Pennsylvania after passengers fought back against the hijackers. Cheney said he received the authorization in an earlier phone call with President Bush."

I still think that it is possible that the 4th plane that crashed in Pennsylvania was shot down. Here is the link to the rest of the article:
9/11 Panel Criticized Military Response to Attacks