This part of ISO 22090 specifies general requirements, construction, performance, and testing of transmitting heading device using GNSS principle as required by chapter V, SOLAS 1974 (as amended). A transmitting heading device (THD) is an electric device that provides information about the ship's true heading. In addition to the general requirements contained in IMO Resolution A.694(17) to which IEC 60945 is associated and the relevant standard for the sensing part used, the THD equipment shall comply with the following minimum requirements. Where the IMO performance standards that apply to the sensing part do not specify a geographical operating area, the THD shall operate a) at a maximum rate of turn 20°/s and b) from 70° latitude south to 70° latitude north as minimum. The THDs complying with the requirements contained in this part of ISO 22090 can be used for heading information as contained in chapter V of the SOLAS Convention. In addition, such THDs should meet the dynamic requirements contained in the HSC Code, chapter 13 for the carriage of a suitable device providing heading information. NOTE 1 Several technologies can be used to detect and transmit heading information. It is illogical to standardize the detection of the heading separately from the transmission of the heading. Therefore, separate parts of this part of ISO 22090 refer to different technologies. The requirements of this part of ISO 22090 only apply to the principle of the GNSS. Other technologies are covered in other parts of ISO 22090. NOTE 2 All requirements that are extracted from the recommendation of IMO Resolution MSC. 116(73) on performance standards for transmitting heading devices are printed in italics. The main changes compared to the previous edition are as follows: — the normative references have been updated; — [TBD]bridge alert management requirements have been added in 5.6 and the test method in 7.10; — Annex A has been replaced with a new Annex on alerts definition, including alert identifiers; — added new Annex B on IEC 61162 interfaces overview.