The Australian Civil Aviation Regulations currently require the carriage of an emergency locator transmitter (ELT) on most flights in Australian airspace. Changes are occurring to the requirements for the carriage of emergency locator transmitters (ELTs). From 1 February 2009, all ELTs must operate on frequencies 406 and 121.5 MHz. Many ELTs currently used in Australia operate on 121.5 and 243 MHz. These ELTs will become unusable after 1 February 2009.