Approximately thirty minutes into the flight , the hijackers forcibly breached the cockpit and overpowered the pilot and first officer , allowing lead hijacker and trained pilot Marwan al-Shehhi to take over the controls . Unlike Flight 11 , which turned its transponder off , the aircraft 's transponder was visible on New York Center 's radar , and the aircraft deviated from the assigned flight path for four minutes before air traffic controllers noticed these changes at 08:51 EDT . They made several unsuccessful attempts to contact the cockpit . Unknown to the hijackers , several passengers and crew aboard made phone calls from the plane to family members and provided information about the hijackers and injuries suffered by passengers and crew
Flight 11
American Airlines Flight 11
United Airlines Flight 175