The flight was scheduled to depart at 08:00 for Los Angeles . Fifty-one passengers and the five hijackers boarded the 767 through Terminal C 's Gate 19 . The plane pushed back at 07:58 and took off at 08:14 from runway 9 , about the same time Flight 11 was hijacked . By 08:33 , the aircraft reached cruising altitude of 31,000 feet , which is the point when cabin service would normally begin . At 08:37 , air traffic controllers asked the pilots of Flight 175 whether they could see American Airlines Flight 11 . The crew responded that Flight 11 was at 29,000 feet , and controllers ordered Flight 175 to turn and avoid the aircraft . The pilots declared that they had heard a suspicious transmission from Flight 11 upon takeoff . " Sounds like someone keyed the mic and said everyone stay in your seats " , the flight crew reported . This was the last transmission from Flight 175
American Airlines Flight 11
American Airlines Flight 11
United Airlines Flight 175