How many planes were hijacked 9 11?

Four planes were hijacked on September 11.

* American Airlines Flight 11 (Boston to LA, crashed into North Tower of World Trade Center) * United Airlines Flight 175 (Boston to LA, crashed into South Tower of World Trade Center) * American Airlines Flight 77 (Washington DC to LA, crashed into the Pentagon) * United Airlines Flight 93 (Newark to San Francisco, crashed into a field in Pennsylvania)