An underwater locating device (ULD) is a crucial component in aircraft safety. Designed to withstand crash impacts, it can be attached to the cockpit voice recorder (CVR), flight data recorder (FDR), or the aircraft fuselage. ULDs emit acoustic pulses, helping authorities locate aircraft wreckage in ocean areas after an accident. Initially, these devices were only linked to CVRs and FDRs, using 37.5 kHz signals. However, newer models can also be installed on the airframe, utilizing an 8.8 kHz frequency.
Recent updates in European aviation regulations have brought important changes. As of January 1, 2020, ULDs connected to flight recorders must transmit signals for 90 days instead of the previous 30 days. Furthermore, by January 1, 2019, larger airplanes flying more than 180 nautical miles from shore were required to have additional low-frequency (8.8 kHz) ULDs. These devices must meet ETSO-C200 standards and should not be installed in wings or tail sections.
Low-frequency ULDs are particularly effective. They have an extended detection range, significantly reducing the time and cost involved in locating wreckage. These devices emit an 8.8 kHz acoustic signal (pinger) for at least 90 days, with a detection range four times greater than standard ULDs, reaching up to 13-22 km (7-12 NM). They can operate at depths of up to 6,000 meters (20,000 feet) and activate in both salt and fresh water. The battery is a single-cell type, lasting six years. The ULD includes a DK180 Beacon, a mounting kit, and an adapter plate.
To keep ULDs functioning properly, an aircraft maintenance program is essential. This program should include testing the ULD during battery replacement to ensure it still operates effectively. Regular maintenance must follow the manufacturer’s guidelines, addressing battery life limits and cleaning switch contacts. When installing the ULD on the flight recorder, care should be taken to position the switch contacts vertically or facing down to prevent debris buildup that could cause accidental shorting.
