47 CFR § 80.1117 - Procedure for receipt and acknowledgement of distress alerts.
(a) Normally, distress calls received using digital selective calling are only acknowledged using a DSC acknowledgement by a coast station. Ships should delay any acknowledgement in order to give sufficient time for a coast station to acknowledge the call. In cases where no acknowledgement has been heard and no distress traffic has been heard, the ship should transmit a distress alert relay to the coast station. Upon advice from the Rescue Coordination Center, the ship may transmit a DSC acknowledgement call to stop it from being repeated. Acknowledgement by digital selective calling of receipt of a distress alert in the terrestrial services must comply with ITU-R M.541-9 (incorporated by reference, see § 80.7).
(b) Acknowledgement through a satellite of receipt of a distress alert from a ship earth station must be sent immediately (see § 80.1119).
(c) Acknowledgement by radiotelephony of receipt of a distress alert from a ship station or a ship earth station must be given in the following form:
(1) The distress signal MAYDAY;
(2) The call sign or other identification of the station sending the distress message, spoken three times;
(3) The words THIS IS (or DE spoken as DELTA ECHO in case of language difficulties);
(4) The call sign or other identification of the station acknowledging receipt, spoken three times;
(5) The word RECEIVED (or RRR spoken as ROMEO ROMEO ROMEO in case of language difficulties);
(6) The distress signal MAYDAY.
(d) The acknowledgement by direct-printing telegraphy of receipt of a distress alert from a ship station must be given in the following form:
(1) The distress signal MAYDAY;
(2) The call sign or other identification of the station sending the distress alert;
(3) The word DE;
(4) The call sign or other identification of the station acknowledging receipt of the distress alert;
(5) The signal RRR;
(6) The distress signal MAYDAY.
(e) The acknowledgement by direct-printing telegraphy of receipt of a distress alert from a ship earth station must be given by the coast earth station receiving the distress alert by retransmitting the ship station identity of the ship transmitting the distress alert.