ELTs serve as an aid in aircraft search and rescue operations.
Aircraft Emergency Locator Transmitters (ELTs) are used as an aid in locating downed aircraft. ELTs begin transmitting immediately upon impact. The Federal Aviation Administration establishes the requirements for aircraft to be equipped with Emergency Locator Transmitters. There are two basic kinds of ELTs: those that transmit on frequencies of 121.5 and 243.0 MHz, and those that transmit on a frequency of 406.0 MHz.
Federal Aviation Regulations
Federal Aviation Regulations (FARs) require aircraft to be equipped with an ELT. Specific requirements are detailed in FAR 91.207. ELTs are required for all aircraft having more than one seat, with some limited exceptions.
Either a 121.5/243.0 MHz or 406.0 MHz ELT satisfies the requirements of the Federal Aviation Regulations. Aircraft owners are not required to switch to the International Civil Aviation Organization (ICAO) requirement for a 406.0 MHz ELT for operations within the United States. Aircraft owners operating internationally, including flights into Mexico or Canada, need to have the ICAO standard 406.0 MHz ELT. There is no longer satellite monitoring of 121.5/243.0 MHz ELTs, and aircraft owners are advised to consider changing to 406.0 MHz ELT transmitters
Regulations require ELT batteries to be replaced after one hour of operation or after 50 percent of the battery’s useful life. The one-hour usage requirement is cumulative–if the ELT is used two times for half an hour each, then the transmitter has been used for a cumulative total of one hour and the battery must be replaced. Battery useful life, for the purpose of battery replacement, is determined by the battery manufacturer. The date of the next required battery replacement must be marked on the ELT and in the aircraft records.
The most common exceptions to the ELT requirements are for aircraft used in training within a 50-mile radius of their base of operations, aircraft used in aerial application (crop-dusters) and aircraft undergoing certification testing. Additionally, an exception is made for operation of an aircraft while the ELT is removed for service or replacement; the aircraft may then be operated without an ELT, providing appropriate entries have been made in the aircraft records and the aircraft is placarded noting that the ELT is not installed. This exception for operation during periods of service or replacement is only applicable for up to 90 days from the date the transmitter was removed for the aircraft.