Description

An underwater locator beacon (ULB), also called an underwater locating device (ULD) or underwater acoustic beacon is a device fitted to aviation flight recorders such as the cockpit voice recorder (CVR), the flight data recorder (FDR) as well as to the aircraft fuselage. Once activated by immersion in water, a ULB is designed to emit an ultrasonic pulse at 37.5 kHz every second for a duration of at least 30 days. ULBs attached to the airframe transmit at 8.8kHz and are called low frequency ULBs.

Note: The abbreviation ULD is also used for Unit Load Devices (ULD), which are containers for baggage and cargo carried in the holds of aircraft.