2872 Safety signal. Working hours serv- ice. Land stations. INTERNATIONAL RADIO CONVEXTION. NOYE.::\1BF.R 25, H)27. in which it is located; of a ship, aircraft, or other vehicle in sight; or finally, of the safety of any person on board or in sight therefrom. In the aircraft radio seryjce the indication PAN shall be used as an urg('nt signal, by radiotelephony and by radiotelegraphy, when an aircraft station wishes to give notice of damage which compels the aircraft to land without requiring immediate assistance. In the case of radiotelegraphy, the three letters must be well separar,ed in order that the signals AN be not transmitted as the signal P. (2) The urgent signal shall have priority over all other communica- tions except those of distress, and all mobile or land stations which hear it must avoid interfering with the transmission (f such urgent traffic. (3) As a general rule, the urgent signal may be employed only if the sending mobile station addresses it to a specific station. §23. (1) Mobile stations which hear the urgent signal must continue to listen for at least three minutes. At the expiration of this period and if no urgent message has been heard, mobile stations may resume their normal service. (2) Land and ship stations nevertheless, which are in communi- cation on authorized waves, other than that used for the transmission of the urgent signal and of the call which follows it, may continue their normal work without interruption. §24. The urgent signal shall be transmitted only with the author- ization from i.;he master or the person responsible for the ship, air- craft, or other mobile station. Safety signal §25. The safety signal shall consist of the transmission of the group TTT, with the letters well separated, followed by the word DE and by the call signal of the station sending it. It shall iildicate that this station is abO'ut to transmit a message concerning the safety of navigation or giving hnportant information relative to meteoro- logical warning messages. §26. The safety signal and the safety message shall be sent on the wave of 500 kc/s. (600 m.) and if necessary, on the normal listening wave of ship and aircraft stations. §27. The safety signal shall be sent once during the first silent period (Article 17, section 2) and near the end of that period. All stations hearing it must continue to listen on the normal calling wave (ship stations) or on the authorized wave (aircraft station) until the message preceded by the safety signal shall have ended. The transmission of this message shall begin immediately after the end of the silent period. ARTICLE 20 Working hour8 of 8tation8 in the mobile 8ervice Land 8tations §1. (1) The service of land stations is, so far as practicable, con- tinuous (day and night). Certain land stations, however, may have a service of limited duration. Each Administration or authorized private enterprise whose right so to do is recognized by the laws of its own country, shall fix the hours of service for land stations subject to its jurisdiction. (2) Land stations whose service is not continuous may not close before having: 1. Finished all operations resulting from a distress call; 2. Exchanged all radiotelegrams originating in, or destined to, mobile stations which are situated within their range of action and have indicated their presence before the actual cessation of work.
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