Answer:
The passengers on Flight 93 had learned from radio and phone calls that other planes had been hijacked, and that they had been used to perpetrate terrorist attacks.
For this reason, shortly after the plane was hijacked, the passengers decided to act, and revolted. Some of them struggled in the cockpit with the hijackers, which resulted in the lost of control of the airplane. The plane eventually crashed in an open field in Pennsylvania at around 10:00 am.
The passengers were very brave, and their actions prevented another terrorist attack, and even more deaths. It is widely believed that the Flight 93 was meant to crash the White House or the Capitol, something that would have been even more devastated for the United States.
