Emergency Locator Transmitter — Origin

• In 1972, two U.S. Congressmen were lost in an Alaskan snowstorm; search and rescue flew over 3,000 hours and found nothing.
• Congress responded with a law requiring aircraft to carry a beacon that automatically senses a crash and sends emergency signals on 121.5 MHz, the distress frequency.
• General Aviation (Part 91) was required to be equipped with an ELT; airlines (Part 121) required ELTs for extended flight over water and uninhabited areas.
• Flaws soon appeared: no guarantee a distress call would be heard, and false alarms rose so high that only a few percent resulted from actual crashes.