Why did the passengers on flight 93 suspect they were part of a larger terrorist plot than that involving a single plane?

Passengers on Flight 93 suspected they were part of a larger terrorist plot when they learned that multiple hijackings had occurred on the same day, including those involving American Airlines Flight 11 and United Airlines Flight 175, which had struck the World Trade Center. Additionally, during their communications with loved ones and authorities, they gathered information about the unfolding situation, leading them to realize that their flight was not an isolated incident. This awareness prompted their courageous decision to fight back against the hijackers.