PLB

PLB stands for Personal Locator Beacon: a portable personal distress beacon used to alert search and rescue services. Once manually activated, it sends a digital distress alert in the 406 MHz band through Cospas-Sarsat. The alert contains a beacon identification code and, on suitably equipped models, may also include the device's GNSS-derived position.

A personal distress beacon during isolation

A PLB is carried by an individual, for example on their body or in their survival equipment. It can send a distress alert without a mobile phone connection. It is not intended for routine position reports or ongoing communication within a group.

In military isolation, this search and rescue alert must be distinguished from a planned recovery procedure. A PLB's identification code does not provide military authentication of the person transmitting the alert. Nor does the alert automatically initiate a particular tactical recovery mission. Responsibility, available forces and agreed procedures remain central to Personnel Recovery.

How the alert reaches a rescue authority

Satellites in the Cospas-Sarsat system receive the distress alert and relay it through ground stations for processing. A Mission Control Centre processes and distributes the alert. It reaches the responsible rescue coordination centre or a national search and rescue point of contact. The responsible rescue coordination centre establishes the circumstances of the emergency and coordinates search and rescue efforts. The responsible authority is not necessarily the geographically nearest coordination centre; information can also be passed between countries.

The identification code distinguishes the individual beacon. Registration links it to details of its user and their contacts. Those contacts can help establish the planned activity, the number of people involved or a possible route. These personal details are held in the register; they are not all transmitted as part of the distress alert. Outdated contact details or an unrecorded change of ownership make it harder to establish the circumstances.

Registration authorities and requirements differ between countries. In the United States, NOAA handles registration of beacons assigned to that country; in Australia, AMSA is responsible.

GNSS position and homing

A built-in GNSS receiver can determine its position and make it available to the PLB for transmission. Determining a position and sending a distress alert are two different functions: an ordinary GPS receiver does not alert a rescue authority on its own. PLB models without an embedded GNSS receiver also transmit their 406 MHz distress alerts through the satellite system.

An additional homing signal, often on 121.5 MHz, helps suitably equipped rescuers approach the beacon within the search area. Its purpose differs from that of the digital 406 MHz distress alert. Whether a device provides additional signals, and which ones, must be checked for the specific model.

Some devices support a return link called the Return Link Service, or RLS. A corresponding indication can confirm that the alert has been detected and the beacon’s location independently determined. The system generates this response automatically; it does not confirm that a rescue operation has already been launched. The responsible rescue coordination centre plans and coordinates the operation. A conversation or free-text exchange requires an additional communications device.

Activation and safe use

A PLB is intended for a serious, life-threatening emergency. It is activated manually. Automatic activation, as provided by certain maritime or aircraft beacons, must therefore not be assumed. Other available means of communication can provide additional information about the situation.

Follow the manufacturer's instructions for activating the beacon, using its antenna and positioning the device. As clear a view of the sky as possible supports the radio link, but this should not involve moving to a dangerous location. Where there is no hostile threat, the activated beacon remains switched on until the rescue authority directs otherwise. Under hostile threat, an open beacon alert can also expose the transmitter's location to adversary receivers. Operation then follows the prepared military communications and recovery instructions. Switching off stops new transmissions and any homing signal provided; leaving the beacon on preserves those locating functions but continues the radio emissions.

Use the designated test procedure to check the device's operation, without triggering a real distress alert. If the beacon is activated accidentally, stop the false alert and inform the responsible rescue authority immediately so that it can identify the alert already received as a false alarm.

PLBs, EPIRBs, ELTs and satellite messengers

Sharing an alert frequency does not make PLBs, EPIRBs and ELTs freely interchangeable. They differ in their intended application, design and activation. Likewise, a satellite messenger with an emergency function is not a PLB simply because it can send a distress alert.

Obstructions affect the radio link; weather, terrain, access and available rescue resources affect the subsequent response.