• How does a PLB work?

• How does GPS work with a PLB?

• How do they know where I am?

• How quick will Search and Rescue respond after I turn on my PLB?

• Who will respond when I turn on my PLB?

• Are there any limitations as to where I can use a PLB?

• Why must a PLB be registered?

• Do I need a PLB if I already have a Cell Phone or a Satellite Phone?

• Does a PLB really work? Will it save my life?

Q: How does a PLB work?

The PLB transmits a coded radio signal that is received by an orbiting satellite. The satellite then re-transmits the signal to a ground station that passes it on to an appropriate Mission Control Center, determined in part by the national code included in the signal. Through the use of sophisticated technology it is possible to determine the location of the source of the distress signal. In the case of some beacons that also transmit location information derived from GPS, the location information is already known. From there, the distress information is passed to the appropriate search and rescue authority for action.

Q: How does GPS work with a PLB?

Whether the PLB receives the GPS location information from an external GPS or an integral GPS chip, the longitude and latitude coordinates are included in the digital data stream sent to the satellite.

This location information is updated once every 20 minutes for beacons with internal GPS. Those with external GPS do not update GPS information unless the beacon is switched off and then on again. Authorities are working to eliminate this from the international specifications, a leftover solution to a situation that is no longer a concern.

Q: How do they know where I am?

Two means are used to determine location.

The basic process involves Doppler shift measurement techniques that allow the low-earth orbiting (LEO) satellites passing overhead to determine a location. The location is determined from the Doppler shift in the carrier frequency. The Doppler effect is the perceived change in frequency resulting from the relative movement of the source, the PLB, and the receiver, the LEO satellite.  As the satellite approaches the PLB, the frequency received by the instruments on board the satellite will be higher than the actual transmitted frequency; as the satellite passes by the source of the signal the transmitted frequency will become lower than the transmitted frequency.

At the point on the Doppler curve that the received and transmitted frequencies are equal, the position of the transmitter will be perpendicular to the satellite ground track. The strong 5 watt 406 MHz signal makes this process easier and more accurate than the older, low-powered 121.5 MHz signal; sufficiently better that a reliable and accurate location can usually be determined on the first pass, not the case with the weaker 121.5 MHz signal which require multiple passes.

Q: How quick will Search and Rescue respond after I turn on my PLB?

If your PLB sends out a GPS location that is received by the geostationary satellites, then search and rescue will often be dispatched within minutes, depending on available resources and your location. 

Even without location information in the coded signal, if initial contact with the Emergency Contacts listed on the Registration Form provides useful location information, response can begin as soon as that information is received, again, often within minutes. 

If location information must waited to be received from the satellite's Doppler location mechanism, it may take up to 90 minutes, though that is more likely 45 minutes or less in the U.S.  If a satellite passes overhead sooner, it will be quicker.

Q: Who will respond when I turn on my PLB?

That will depend upon your location.

Typically, the Coast Guard responds to marine distress, but they may also utilize appropriate local or state assets if available and closer.

Inland distress is generally the responsibility of local law enforcement, typically a county sheriff in much of the U.S. often with the assistance of local volunteer search and rescue teams.  These may call upon federal or state assets if available. 

The Civil Air Patrol generally responds to an aviation distress signal in most states in the U.S., and historically this has been primarily because generally extensive air search is necessary to locate the inaccurate 121.5 MHz beacon. In most cases of a 406 MHz PLB alert they will not be activated unless indications are that it comes from a downed aircraft and that local SAR resources cannot locate and take care of it in short order. That downed aircraft indication will come from providing that data in the Additional Data section, or from the Emergency Contacts listed on the registration form.

In most cases these days where the PLB alert is a remote location, the first assets to arrive will be airborne, typically a helicopter from the closest SAR resource, regardless of who operates it.

Q: Are there any limitations as to where I can use a PLB?

Geographically, a PLB may be used anywhere on the globe, there are no physical or legal restrictions in that regard. PLB activation is prohibited anywhere that radio transmissions are prohibited, including on commercial airlines in flight, in explosives storage and blasting areas, etc.

Q: Why must a PLB be registered?

It could save your life and it can also save taxpayer money and avoid putting rescuers' lives at risk unnecessarily. Time is often the critical difference between a successful rescue and retrieval of bodies.  Having spent the money for a PLB, it would be foolish to shortchange yourself on one of its most important capabilities by not registering.

One of the major advantages of the 406 MHz beacons is the digital coding and registration. This allows for instant identification of who is in distress.   Using the information in the registration, authorities can often determine with a quick phone call if it is a false alert or if it is likely a real alert. Further detective work can often yield the likely location of the distress call before satellite location is determined (for those without GPS location information), allowing search planning to begin immediately, and in some cases, allow the immediate launch of a rescue effort.

Q: Do I need a PLB if I already have a Cell Phone or a Satellite Phone?

While cell phones have often been used to summon aid in emergencies, even from offshore or in wilderness areas, their reliability for such use is the real issue. Cell phones often do not work in remote areas, as well as not working reliably in even not so remote areas where there is physical terrain interference. For a variety of reasons in an emergency you may not be able to change location to a mountain or hilltop where you might be able to connect.

Even with a cell phone, you will need some means to provide accurate location information in order for someone to come rescue you.

A satellite phone makes a very nice adjutant to a PLB. However, satellite phones have coverage limitations, no matter what their maps show, are easily blocked by even a moderate forest canopy or high terrain, are not very abuse resistant and are not waterproof (unless packed inside a waterproof container). All have only rechargeable batteries with very limited life.

Q: Does a PLB really work? Will it save my life?

Yes, they work. A test program conducted in Alaska since 1994 has about 400 persons saved to its credit with 378 PLBs registered (many are rentals/loaners used by multiple persons). In 2002 there were 27 rescued in 18 events. Worldwide, where the PLBs have been available for years, numerous rescues have resulted from PLB use.

Like all distress signaling devices, PLBs have limitations. However, when operated properly in accordance with their design criteria and the inherent technical limitations of any radio signaling device, in most cases a PLB will significantly improve your chances of surviving whatever peril you might find yourself in. There are no guarantees and carrying a PLB is not a substitute for using common sense and abiding by good safety practices, but a PLB will generally tilt the odds in your favor. 

Fire & Safety Group does not warrant or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process presented here.