Abstract: A communication system for an aircraft, comprising a plurality of radios including at least a first radio that is operable in an encrypted mode for transmitting/receiving encrypted audio signals, and a second radio that is operable in a clear mode for transmitting/receiving unencrypted audio signals; an intercom system that interconnects the plurality of radios, wherein the plurality of radios is connected to the intercom system via a plurality of communication lines; and a security module that is configured to connect or disconnect selected ones of the plurality of communication lines for inhibiting simultaneous transmission of an encrypted audio signal via the first radio and an unencrypted audio signal via the second radio.