Definition. ICAO defines an Emergency locator transmitter (ELT) as equipment which broadcasts distinctive signals on designated frequencies and, depending on application, may be automatically activated by impact or be manually activated.

An ELT (Emergency Locator Transmitter) is a critical piece of safety equipment required on almost all U.S.-registered civil aircraft. Its primary function is to transmit a distress signal in the event of an aviation accident, allowing search and rescue (SAR) teams to locate the wreckage quickly. In 2026, the aviation industry has almost entirely transitioned to 406 MHz digital ELTs, which are much more accurate than the legacy 121.5 MHz analog models. These modern units are often "automatically activated" by G-forces (impact) or water immersion, though they can also be triggered manually by the pilot. Once activated, the 406 MHz signal is picked up by the COSPAS-SARSAT satellite system, which transmits the aircraft's unique ID and, in most cases, its precise GPS coordinates to a Rescue Coordination Center. This technology has reduced the average search time from days to minutes, significantly increasing the "golden hour" survival rates for pilots and passengers involved in remote area accidents.