...acknowledged navigational instructions from the FAA’s air traffic control (ATC) center in Boston. Sixteen seconds after that transmis- sion,ATC instru... ... was abnormal on United 175 came at 8:47, when the aircraft changed beacon codes twice within a minute.At 8:51, the flight deviated from its assigned ... ...ican 11 said “we have planes.”At the same time, New Y ork Center declared “ATC zero”—meaning that aircraft were not permitted to depart from, arrive a... ... Agency, which intercepts and analyzes foreign com- munications and breaks codes.The NSA also creates codes and ciphers to pro- tect government inform... ...o perform “traffic analysis”—studying technical communications systems and codes as well as foreign organizational structures, including those of terr... ..., Sept. 11, 2001;AAL tran- script, telephone call from Bill Halleck to BOS ATC, Sept. 11, 2001.The Air Carrier Standard Security Program required airl... ...tor, we could find no evidence that a nationwide warning was issued by the ATC system. 68. Ellen King interview (Apr. 5, 2004). FAA air traffic contro... ...thus his attempts to communicate with the passengers were broadcast on the ATC channel. See FBI report,“CVR from UA Flight #93,” Dec. 4, 2003.Also, by... ...hin 1 second, are airplane- and crash-site specific, and are based on time codes automatically recorded in the ATC audiotapes for the FAA centers and ...