A distress beacon is an emergency transmitter that sends radio signals for alerting and locating after manual or automatic activation. The umbrella term includes personal beacons, maritime beacons and aircraft emergency locator transmitters. For isolated personnel, a beacon can provide the first indication of distress and a starting point for a search. The location obtained is the transmitter's: a beacon left at a wreck, lost or drifting separately indicates a different place from a person who has since moved away.
Alert, identification and position
A digital 406 MHz distress beacon includes a beacon identification code in its alert message. Registration links that code to information about the owner, associated aircraft or vessel, and nominated emergency contacts. These details are held in a registry; the beacon does not transmit a complete account of the current situation with every alert. A registered device helps the receiving authority assess the alert and obtain further information. It does not report how many people remain together, their injuries or a new enemy threat.
The Cospas-Sarsat satellites receive the signal and relay it to a ground receiving station, the local user terminal. The processed alert data then go to a mission control centre, which combines messages and distributes them to the responsible search and rescue authorities. A rescue coordination centre handles the alert and coordinates available resources. This path connects the beacon to an alerting organisation. It does not establish a voice link to the person's unit or a recovery vehicle.
An integrated global navigation satellite system receiver, or GNSS receiver, can calculate position from received satellite signals; the beacon then adds those data to its alert message. An ordinary navigation receiver calculates its own location but does not thereby send it to search forces. Transmission requires the distress transmitter or another communications device. The satellite system can also locate the transmitter from its signals without an encoded navigation position. Receiving an alert and obtaining a usable location are separate processes. Where an aircraft position has been supplied only once, the transmitted coordinate may also predate the crash or subsequent movement.
An additional homing signal helps suitably equipped search forces approach the beacon by air or on the ground. It leads them to the transmitter even if its carrier is no longer there. Older devices that provide only an analogue homing signal require a receiver within range; that signal does not generate a Cospas-Sarsat satellite alert.
Which beacon remains with the person?
| Type | Purpose and activation | Significance during isolation |
|---|---|---|
| PLB | Personal, portable distress beacon; manually activated. | It must be carried within reach and activated by the user. If it remains on the person, the transmitter's location moves with them; loss or equipment left behind separates the two. |
| EPIRB | Maritime distress beacon; manual or automatic release and activation, depending on design. | A released, floating beacon can drift separately from survivors. Securing it as designed to a person or life raft keeps its location associated with the group. |
| ELT | Aircraft emergency locator transmitter; fixed, removable or automatically deployed designs. | A fixed transmitter provides a starting point at the aircraft. Only a device designed for portable use and actually available to the survivors can remain with them after they leave. |
An EPIRB's flotation characteristics do not mean that a PLB will also transmit upright in water. Similarly, an automatically activated aircraft ELT does not provide a personal beacon after a parachute escape. Before a mission, the person must know which device stays with the vehicle, which is accessible during emergency escape, and which antenna is needed for operation away from the vehicle. Dismantling a fixed transmitter does not substitute for a version designed for portable use.
Preparation and operation by the person
Preparation includes the correct beacon code in the responsible registry, current contact and associated vessel or aircraft details, a serviceable battery and the specified self-test. Registry details need updating after loss or a change of associated vessel or owner. The self-test checks the device functions intended for that test; activating a normal distress alert as a trial can trigger a real alert. The test procedure and permitted frequency depend on the device, since testing also consumes battery power. After actual use, battery depletion and damage may require servicing.
During isolation, the equipment decision begins with what actually remains: beacon, appropriate antenna, power supply and, if available, another radio. For a manually operated beacon, the intended release mechanism, antenna deployment, activation and meaning of its indicators matter. An operating indicator shows the local device status. Only a suitably equipped device can receive confirmation of alert reception and forwarding through the Return Link Service; that indication does not confirm that a rescue operation has been launched.
A portable beacon needs its intended antenna position and as unobstructed a view of the sky as possible. The body, vehicle components, buildings and steep terrain can obstruct the radio paths. Covering the antenna or navigation receiver with the body further worsens reception conditions. On water, a PLB must remain above the surface; an EPIRB designed for the purpose floats in its transmitting orientation and is secured to something that will not sink. Under enemy threat, positioning also requires considering whether deploying the beacon exposes the person to observation. An open high point with the best sky view can therefore be an unsuitable place to remain.
A broken antenna or depleted battery can prevent transmission; a beacon left behind is unavailable to the person for further position reports. If the person must leave a dangerous wreck or transmitter location and an active beacon stays behind, further alert or homing signals come from that device. Location information derived from them concerns the beacon rather than the person's continuing movement. A movement intention recorded beforehand, for example in an evasion plan of action, provides an additional lead for search forces; it does not transmit continuing position changes. Those require a transmitting device actually carried by the person and a reachable receiver.
Alerting and military recovery
An open distress beacon alert can also expose the transmitter's location to an adversary; its digital identification code does not protect the alert data from reception by others. Military multifunction devices may provide additional links: CSEL has protected two-way data communications and separately unsecured SARSAT data modes. The protection of one data link therefore cannot be applied to every mode of the same device. Signal type and switching times depend on the issued device and prepared instructions for the specific recipient and threat. Switching off also stops new transmissions and any active homing signal.
With an established two-way link, the person can report a current location with its time reference, injuries, number of people, movement and hazards, and answer questions. This enables search forces to handle the situation with more information than a beacon alert supplies. Before military recovery, the agreed personnel authentication procedure remains necessary: a recognised beacon may have been lost, found or separated from its user. The prepared information and procedures for verifying the person's identity serve a different purpose from technically identifying the beacon code.
The alerting organisation depends on the area concerned and participating national authorities. In the United States, the mission control centre links the code to the NOAA registry; distribution to Air Force or Coast Guard rescue coordination centres depends on the type and location of distress. For an Australian-registered beacon activated abroad, AMSA provides available registry and emergency contact information while the responsible authority in the area conducts the search. Within NATO, equipping isolated personnel is also a national responsibility. Prepared forwarding arrangements must therefore connect the actual beacon alert with the military personnel recovery organisation. Weather, terrain, enemy threat and reachable forces then determine which support or recovery is feasible.