This part of ISO 22090 specifies the construction, performance, and testing of gyro-compasses as transmitting heading device required by chapter V, SOLAS 1974 (as amended). A Transmitting heading device (THD) is an electronic 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 that the THD shall operate a) at 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. However, ships within a speed range of 30 kn to 70 kn should comply with the requirements of IMO Resolution A.821(19). In addition, such THD 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 gyroscopic technology. Other technologies are covered in other parts of ISO 22090. NOTE 2 All requirements that are extracted from the recommendations of IMO Resolution MSC. 116(73) on performance standards for transmitting heading devices are printed in italics. The main changes compared to the present edition are as follows; — Requirements related to bridge alert management (BAM) will be added to the clause of requirements and type test. — IEC 61162-450 will be added to the clause of interface as an option. — The normative references and bibliography will be updated. — Editorial revision of the standard in general according to the ISO/IEC Directives, Part 2 — Additionally, Annex will be added as alert definitions and IEC 61162 interface overviews for further explanation of the above.