Definition

An underwater locating device (ULD) is an aircraft installation which is designed to survive the impact of a crash. The device may be attached to the cockpit voice recorder (CVR), the flight data recorder (FDR) as well as to the aircraft fuselage. The ULD are devices that emit acoustic pulses permitting authorities to locate aircraft wreckage when an accident happens in oceanic areas. ULDs were initially only attached to CVRs and FDRs (37.5 kHz ULDs) and now an additional ULD can be attached to the airframe (8.8 KHz ULDs).