Sec.  80.328   Urgency message.

   (a) The urgency signal and call, and the message following it, must be sent
   on one of the international distress frequencies. Stations which cannot
   transmit on a distress frequency may use any other available frequency on
   which attention might be attracted.

   (b) Mobile stations which hear the urgency signal must continue to listen
   for at least three minutes. At the end of this period, if no urgency message
   has been heard, they may resume their normal service. However, land and
   mobile stations which are in communication on frequencies other than those
   used for the transmission of the urgency signal and of the call which
   follows it may continue their normal work without interruption provided the
   urgency message is not addressed “to all stations”.

   (c) When the urgency signal has been sent before transmitting a message “to
   all stations” which calls for action by the stations receiving the message,
   the station responsible for its transmission must cancel it as soon as it
   knows that action is no longer necessary. This message of cancellation must
   likewise be addressed “to all stations”.