GPS Feature of EPIRBs

Foundation Findings #39 - July 2004

In March 2003, the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Coast Guard organized a test to determine the answer to a very troubling question: why, in 66% of real-world activations of GPS-enabled emergency beacons, were the GPS coordinates not transmitted to search and rescue authorities as they should have been?

This test—referred to as the Key West Test—was requested by representatives of COSPAS-SARSAT, the international, satellite-based distress alerting system that monitors emergency transmissions around the world. Originally, the test was conceived to see if there was a weakness in their system of receiving distress alerts from mariners, pilots, and inland wilderness travelers in trouble, however once the Key West Test was completed, another issue surfaced.

While the core function of the EPIRB – the 406 MHz distress signal—was reliable and could provide an approximate location of the distressed vessel via Doppler, not all the beacons performed the additional function of transmitting their GPS coordinates, which would give rescuers exact coordinates. In other words, some of the beacons were not performing as advertised.

This discovery disturbed those involved with the test and those privy to the results. Essentially, consumers were paying a premium for EPIRBs they believed had capabilities that could increase their chance for survival in an emergency—and some models clearly weren’t meeting those claims. The problem was that emergency beacon manufacturers had allowed their units to be tested in the Key West Test with the understanding of anonymity.

To confirm the Key West Test and ensure the results were made public, a second set of tests was conducted by the nonprofit Equipped To Survive Foundation and sponsored in part by West Marine and the BoatU.S. Foundation for Boating Safety and Clean Water.

While the core function of the EPIRB – the 406 MHz distress signal—was reliable and could provide an approximate location via Doppler, not all the beacons performed the additional function of transmitting their GPS coordinates, which would give rescuers exact coordinates.

How They Work

Global Positioning System (GPS)-enabled Emergency Position Indicating Radio Beacons (EPIRBs) have been available for several years, often used by offshore boaters. Personal Locator Beacons (PLBs) have been available in the continental U.S. since 2003, but have been used elsewhere for some time. These can be clipped to the life jacket of an offshore mariner, or carried by a backpacker or a wilderness kayaker. We’ll only be discussing the marine applications here.

In a severe emergency, you would activate your EPIRB or PLB by flipping a switch. The beacon then transmits on the 406 MHz frequency a digital distress signal detected by the COSPAS-SARSAT Satellite Distress Alerting System. After processing the digital data from your signal, appropriate search and rescue authorities are notified. Provided you have registered your EPIRB with NOAA as required, authorities will also be able to access information about your vessel, emergency contacts, and how many are aboard.

There are two main advantages to using a GPS-enabled beacon over a “standard” 406 MHz beacon. First, search and rescue authorities will not only receive your distress signal, but they should receive your exact GPS coordinates. Without these GPS coordinates, the authorities can narrow your position down to a radius of about two nautical miles via Doppler. Combined with a GPS, the unit’s location can be pinpointed to within a half nautical mile or less. Second, your vessel’s position is transmitted much quicker when the GPS coordinates are available. It takes about three to five minutes for your location to register with authorities when you are using a properly-working GPS-enabled EPIRB. Depending on the position of satellites passing overhead, it could take up to 90 minutes for a standard 406 MHz EPIRB’s position to be reported.

Standard 406 MHz EPIRBs are highly-trusted as a safety tool, and are even rented through the BoatU.S. Foundation by the week. However, GPS-enabled EPIRBs are seen as an upgrade and can cost up to 50% more. With this comes the expectation that one’s rescue will be more likely and time spent in the water will decrease.

The Latest Tests

The second series of test were conducted in January 2004, on and off the coast of Santa Cruz, CA. Equipped To Survive Foundation conducted the testing and representatives from the BoatU.S. Foundation, West Marine, the U.S. Coast Guard and NOAA attended, as well as representatives from some beacon manufacturers and other companies and agencies.

Observers aid Equipped to Survive in testing by acting as distressed mariners during the life raft testing of the McMurdo Precision 406 EPIRB. The EPIRB is in the center of the raft, typical of where all the beacons were situated for the tests.

All beacons legal and available in the U.S. at the time of testing were included. Five were off-the-shelf models from ACR Electronics and McMurdo Ltd. The sixth was a Techtest GPS PLB not readily available to consumers, and the company paid for its inclusion in the testing. Two of the models tested required an external GPS to be plugged in (see chart). All others contained an internal GPS.

Baseline testing began with the beacons stationary on a jetty, with open, uninterrupted access to the sky and the GPS satellites. All beacons were activated using a test code so authorities would know it was not an actual emergency. On the jetty, all six activated beacons were able to lock on satellites (in other words, “acquire satellites”) and successfully transmit GPS coordinates with their distress alert.

Next, to test the beacon’s ability to “refresh” its position every 20 minutes, which would be useful if you were in a drifting life raft or disabled boat, the beacons were then hand-carried 400 yards and their GPS readings checked at the 20-minute update. Here was the first sign of trouble. The McMurdo Fastfind Plus PLB failed to update its position, even after it was allowed to remain on through a second 20-minute cycle. In the remainder of the baseline testing, all units except the McMurdo PLB performed as expected.

Next, during maritime testing, the six beacons were put through simulated boating emergencies in the Pacific Ocean. When activated out on the water, all the beacons reliably transmitted an emergency alert, however the McMurdo beacons—both the EPIRB and PLB—failed to transmit GPS coordinates when activated, even when the tester’s control GPS was showing ample satellites in view. In test after test, the McMurdo beacons could not lock on satellites within the first 30 minutes of operation—the COSPAS-SARSAT certification requirement.

The first failure occurred on a sailing vessel in eight foot swells, with clear and dry conditions and few obstructions to the horizon save for the mast overhead and the people sitting around the beacon. Neither McMurdo beacon could acquire satellites though all other beacons had no trouble. During the remainder of maritime tests, the McMurdo beacons continued to have difficulty acquiring satellites and failed to transmit GPS coordinates in every subsequent planned maritime testing scenario (see chart).

Concerned by the findings, the testers put the McMurdo Precision GPS EPIRB to an additional test not part of planned test protocol. In one to two foot, mirror-smooth seas, and in clear weather, it was allowed to float free, as opposed to being tethered, which causes additional jerky movement.

Here, in near perfect conditions, the McMurdo EPIRB was able to acquire satellites and transmit its GPS coordinates when activated.

There were two other instances of failure in the maritime testing. The ACR GlobalFix EPIRB failed to transmit coordinates when in the water tethered to the RIB and being sprayed with water. The Techtest PLB failed to transmit from the life raft with the canopy open.

Cause for Concern

Again, it’s important to note that all beacons reliably transmitted emergency signals; signals identical to those of a standard (non GPS-enabled) 406 MHz EPIRB. It was the repeated failure of the GPS feature in the McMurdo beacons in all but ideal conditions that concerned the testers.

Ideal situations, however, are really the only type of certification testing asked of GPS-enabled EPIRBs. COSPAS-SARSAT certification is made up of lab tests which do not reflect the unpredictable nature of the marine environment. We learned through maritime testing that a GPS signal is difficult to find and maintain in the presence of rain, saltwater, and obstructions like metal, rock—and even people. Movement only compounds the difficultly. So while McMurdo may have sold a product that did not perform as promised in all situations, they did meet what was required of them by COSPAS-SARSAT when the beacons performed flawlessly in minimally challenging situations. Could it be that COSPAS-SARSAT standards are simply not stringent enough?

What Now?

Above all, consumers should keep faith in the COSPAS-SARSAT Satellite Distress Alerting System and 406MHz beacons in general. It is specifically the failure of some to transmit additional GPS coordinates as promised that has brought attention industry wide. Before the Key West Test, as long as emergency beacons met COSPAS-SARSAT standards, they were approved by the Federal Communications Commission before being sold to the public. With the new results, the question is: who is responsible for making sure manufacturers meet their claims? And furthermore, are the testing standards—lab tests under ideal circumstances—rigorous enough? Equipped To Survive Foundation Executive Director Doug Ritter recommends that COSPAS-SARSAT standards “more accurately reflect and test for real-world operational performance” as the current GPS-related certification process is inadequate in light of their testing.

West Marine was quick to respond by removing the units in question from all West Marine and BoatU.S. stores and offering refunds to customers who wanted to return the product. Some other retailers are doing the same. In May, the Radio Technical Commission for Maritime Electronics added the issue to their annual conference agenda. This international nonprofit monitors maritime radio navigation and radio communication issues worldwide. At the time of printing there was no information yet on if they planned action in response to the results of this testing.

Representatives from McMurdo, Ltd. say they are puzzled by the results and plan to conduct their own series of tests. Additionally, they plan to offer owners of their GPS-enabled beacons a software and firmware upgrade. As this goes to print, details of the planned tests and how to upgrade the beacons were not yet available. Equipped To Survive Foundation has announced plans to conduct independent tests of these upgraded McMurdo beacons.

For the latest details of this developing story, or for the complete Equipped To Survive Foundation summary report, please visit Equiped to Survive.