47 CFR § 80.324 - Transmission of distress message by station not itself in distress.
(1) When the station in distress cannot transmit the distress message.
(2) When the master or person responsible for the ship, aircraft, or other vehicle not in distress, or for the land station, believes that further help is necessary.
(3) When, although not in a position to assist, it has heard a distress message which has not been acknowledged. When a mobile station transmits such a distress message, it must notify the authorities who may be able to assist.
(b) Transmission must be made on the international distress frequencies or on any other available frequency on which attention might be attracted.
(c) Transmission of the distress message must always be preceded by the call indicated below, which must itself be preceded whenever possible by the radiotelegraph or radiotelephone alarm signal. This call consists of:
(1) When radiotelegraphy is used:
(i) The signal DDD SOS SOS SOS DDD:
(ii) The word DE;
(iii) The call sign of the transmitting station, sent three times.
(2) When radiotelephony is used:
(i) The signal MAYDAY RELAY, spoken three times;
(ii) The words THIS IS;
(iii) The call sign or other identification of the transmitting station, spoken three times.
(d) When the radiotelegraph alarm signal is used, an interval of two minutes must be allowed, whenever this is considered necessary, before the transmission of the call mentioned in paragraph (c)(1) of this section.