How many planes were involved in 9/11?

There were four planes involved in 9/11.

-American Airlines Flight 11 - World Trade Center - North Tower

-United Airlines Flight 175 - Two World Trade Center

-American Airlines Flight 77 - Pentagon

-United Airlines Flight 93

4 1 in Pennsylvania, 1 hit the pentagon, and 2 at the World Trade Center 1 hit each tower.