47 CFR 80.325 - Control of distress traffic.
(a) Distress traffic consists of all messages relating to the immediate assistance required by the mobile station in distress. In distress traffic, the distress signal must be sent before the call and at the beginning of the preamble of any radiotelegram.
(b) The control of distress traffic is the responsibility of the mobile station in distress or of the station which has sent the distress message. These stations may delegate the control of the distress traffic to another station.
(c) The station in distress or the station in control of distress traffic may impose silence either on all stations of the mobile service in the area or on any station which interferes with the distress traffic. It must address these instructions “to all stations” or to one station only, according to circumstances. In either case, it must use one of the following signals which are reserved for use by the mobile station in distress and for the station controlling distress traffic:
(1) In radiotelegraphy, the abbreviation QRT, followed by the distress signal SOS.
(2) In radiotelephony, the signal SEELONCE MAYDAY.
(d) If essential, any station of the mobile service near the ship, aircraft, or other vehicle in distress may also impose silence. It must use for this purpose:
(1) In radiotelegraphy, the abbreviation QRT, followed by the word DISTRESS and its own call sign;
(2) In radiotelephony, the word SEELONCE, followed by the word DISTRESS and its own call sign or other identification.