Emergency Locator Transmitter

An Emergency Locator Transmitter (ELT) is a device that transmits a distress signal on the international emergency frequency (406 MHz for satellite detection, and 121.5 MHz for local homing) to aid search and rescue operations in locating an aircraft after an accident or forced landing.

Types of ELTs include:

• Automatic Fixed (AF): Permanently installed, activated automatically by G-forces upon impact
• Automatic Portable (AP): Removable, automatically activated on impact
• Survival (S): Manually activated by survivors after evacuation
• Automatic Deployable (AD): Ejected and activated automatically upon impact or immersion in water

Modern 406 MHz ELTs transmit a coded signal that is received by the Cospas-Sarsat satellite system, which can determine the transmitter's location to within approximately 5 km. GPS-equipped ELTs provide position accuracy to within 100 meters. ICAO requires ELTs on most aircraft, and the transition from older 121.5 MHz-only units to 406 MHz units is now largely complete worldwide.