Equipped To Survive Foundation 406 MHz GPS Enabled Emergency Beacon Evaluation

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NOTE: The Equipped To Survive Foundation conducted a second evaluation of 406 MHz Location Protocol (GPS enabled) Emergency (Distress) Beacons (EPIRBs and PLBs) in July, 2005. Click here to go to the Second 406 MHz Location Protocol Distress Beacon Evlauation Report.

In December 2003 and January 2004 the Equipped To Survive Foundation conducted a series of laboratory and real-world performance tests of 406 MHz Location Protocol (GPS enabled) Emergency (Distress) Beacons (EPIRBs and PLBs) in an effort to determine how these beacons would perform in real-world conditions. This evaluation was primarily concerned with the self-locating performance of these beacons in real-world conditions, as well as other lesser issues, and not the beacons' performance vis-à-vis COSPAS-SARSAT or other regulatory standards, per se.

The conduct of this evaluation required considerable financial and equipment resources beyond that normally available to the Equipped To Survive Foundation. Sponsorship for the evaluation was solicited, both of financial assistance and of gifts in kind.

The two primary outside financial sponsors were:

BoatU.S. Foundation for Boating Safety & Clean Water (Alexandria, Virginia, USA), a non-profit 501(c)(3) organization that creates education and outreach campaigns, researches issues and products, and helps boaters and user groups learn specific actions they can take to be safer and better stewards of the environment while boating.

West Marine (Watsonville, California, USA), a major U.S. headquartered, publicly traded marine chandlery chain and purveyor of marine safety equipment, both wholesale and retail. In addition, West Marine hosted the testing logistics out of their headquarters building, provided added logistical support, provided boats and equipment necessary for the marine testing, and assigned two employees to assist for the duration of the testing, as well as additional support both prior to and after the actual field testing.

Click here for a complete list of sponsors and donors including contributors of equipment and assistance, without which this evaluation could not have been conducted.

Background to the Evaluation

Key West Test participants observing baseline testing of ACR GlobalFix EPIRB

NOAA (U.S. Department of Commerce's National Oceanic & Atmospheric Administration) and the U.S. Coast Guard organized a test of 406 MHz location protocol (GPS enabled) distress beacons in Key West, Florida, in March 2003, with a limited retest of one company's beacons in May 2003 in Hawaii. The testing was an effort to determine, at the request of COSPAS-SARSAT, why approximately 66% of all actual real-world alerts from GPS-enabled beacons (mostly EPIRBs) did not include the GPS-derived location coordinates, thus potentially slowing response to these emergencies. A report on this test was presented to COSPAS-SARSAT on June 11, 2003. (Link to report opens a new browser window. Download a free PDF Reader)

The bulk of the testing was based at U.S. Coast Guard Group Key West facilities and has come to be referred to as the "Key West Test." In addition to Coast Guard and NOAA representatives, also attending were representatives from NASA, U.S. Air Force Rescue Coordination Center (AFRCC), COSPAS-SARSAT Secretariat (from the U.K.), and five beacon manufacturers (ACR Electronics, Artex, McMurdo Ltd., Microwave Monolithics, and Techtest Ltd). Also present was Doug Ritter, executive director of the Equipped To Survive Foundation, which provided some logistical support to the organizers as well as serving as an independent observer. As part of the agreement to encourage participation by the manufacturers, all results of the testing have been deidentified and participants agreed not to publicly identify particular beacons or discuss the performance of other manufacturers'real world performance levels be achieved beacons.

Key West Test participants observing recording of baseline data for McMurdo FastFind Plus PLB

While conceived and conducted as a system test, the unexpected results of the testing showed that in other than ideal conditions, and in some cases even in ideal conditions, some beacons did not reliably provide location data within the first 30 minutes of operation. That was the testing limit established relating to the COSPAS-SARSAT certification requirements and beacon operating schemes. These beacons ostensibly meet all COSPAS-SARSAT requirements and have been so certified. In the case of the self-locating EPIRBs, the units have been for sale for a number of years. PLBs were first offered for sale in the continental U.S. in July of 2003, but have been available elsewhere in the world for some time.

Retailers report that sales of GPS enabled EPIRBs and PLBs have been very strong, despite incurring a considerable price premium. In interviews they suggest that a significant factor in these sales is the expectation on the part of consumers, based on promotion by the beacon manufacturers, SAR organizations and others, including the Equipped To Survive Foundation, of quicker notification and rescue from their distress circumstances. If the beacons do provide the location data, this is a reasonable expectation. Consumers have been willing to pay a premium of up to 50% for beacons with internal GPS to gain advanced distress alerting capability, which it appeared from the Key West Test results they may not necessarily reliably receive nor receive equally from all manufacturers' beacons.

Key West Test maritime scenario testing of ACR GlobalFix EPIRB

The results of the Key West Test have not been able to be made public in a manner that provides the consumer easy access or understanding due in large part to the deidentification of the beacons required of the participants. In addition, the statistical analysis in the report is flawed in that it combined baseline tests with operational scenarios, artificially inflating the apparent success rate. It was also not specifically conducted as a test of the beacons, which opened it to some criticism and second-guessing regarding any assumptions made as a result of the performance witnessed. Moreover, the regulatory bodies have been unable or unwilling to take any remedial action due to the anonymity promise of the Key West tests, and the fact that the beacons have been certified by COSPAS-SARSAT and the FCC as meeting the regulatory requirements, which is the only statutory or regulatory obligation. One of the report's recommendations was, "Consider whether the 406 MHz Beacon Type Approval Standard (C/S T.007) adequately tests the acquisition of GPS location in operational conditions..." There is no indication that any such consideration is being treated as a priority or that it would result in a change to the standards in the near-term.

Meanwhile, absent any practical means to discriminate among beacons based on performance, consumers are purchasing these beacons that, if the results of the Key West Test were to be believed, do not appear to reliably provide the additional lifesaving benefits that consumers have been led to believe that they will provide, and which consumers have every right to expect to receive, especially so since they are paying a premium for them.

Key West Test participants observing inland scenario test with obscured sky view

Until the Key West Test, the assumption throughout the government entities regulating these devices, the Search and Rescue community, retailers, and consumers alike has been that COSPAS-SARSAT certification was assurance that the emergency beacons all performed adequately, and that there was not a significant difference in distress alerting and self-locating performance between beacons utilizing GPS to obtain location information.

In part this assumption may have been aided and abetted because it is so difficult and expensive to conduct independent consumer-driven testing. As a result, consumer reporting on distress beacons has been primarily focused on easily distinguished differences in physical design, ergonomics, size, weight, and price and the gross performance differences that have been assumed to exist between various modes of operation, external vs. integral GPS, but not actual tested performance as is the standard for most such reporting.

Assuming the results were valid, the Key West Test suggested that the COSPAS-SARSAT certification testing cannot be relied upon at this time to ensure a comparable minimum level of performance among the various beacons on the market. Again, assuming the results of the Key West testing were valid, neither did it appear that marketplace competition or concerns over liability have encouraged adequate or better real world performance levels to be achieved by all manufacturers.

These apparent performance deficits could have profound and potentially fatal consequences, as well as leaving the industry and COSPAS-SARSAT system open to potentially devastating negative publicity and liability, if a beacon's inadequate self-locating performance resulted in loss of life in circumstances where it would otherwise likely have resulted in a successful rescue due to the advantages that self-location would have been expected to provide.

The Equipped To Survive Foundation determined that there was a need to conduct an independent test of these beacons unrestricted by the limitations imposed upon the participants in the Key West Test, and with results that could be communicated to consumers. Consumers have an expectation that emergency lifesaving equipment will perform exceptionally reliably and to its maximum potential if needed to save their life. Consumers have a need for a means to determine if lifesaving equipment will meet these expectations, and the Equipped To Survive Foundation has a history of testing such equipment in order to provide this independent and unbiased information to consumers.

In addition, government regulators and standards-setting organizations have a need to determine if their regulations and standards designed to ensure minimum acceptable performance of lifesaving equipment in the real world are actually doing so. Such testing would also serve to determine if the performance witnessed in the Key West Test was an anomaly or if these results were reproducible, and therefore, the results validated.

The following 406 MHz beacon manufacturers who offer GPS enabled beacons were invited to participate on the basis that they either were currently offering their EPIRBs and PLBs for sale in the U.S. or were anticipated to do so in the near future:

• ACR Electronics, Inc. (Ft. Lauderdale, Florida, USA – a subsidiary of Chelton/Cobham PLC, United Kingdom)
• McMurdo Ltd. (Portsmouth, United Kingdom – a subsidiary of Chemring Group PLC, United Kingdom)
• Microwave Monolithics (Simi Valley, California, USA)
• SERPE-IESM sold under the brand name KANNAD (Guidel, France)

Techtest Ltd. (Herefordshire, United Kingdom - a subsidiary of HR Smith Group, United Kingdom), who offer their PLB as a Survival ELT (aviation Emergency Locator Transmitter) or as a military PLB in the U.S., not as an FCC-approved PLB, and were therefore not originally invited, requested to participate.

Microwave Monolithics and SERPE-IESM declined to participate and since their GPS-enabled PLBs were not yet available for sale in the U.S. and were unobtainable by the organizers, they were not tested.

Due to financial constraints and considering that Techtest was not a significant factor in the consumer marketplace due to its high price and limited distribution as a survival ELT, Techtest was advised that we would be unable to include their beacons in the evaluation. They countered with an offer to finance their inclusion in the testing. After consultation with the primary sponsors, it was agreed that they would be allowed to participate if they paid the pro rata portion of the anticipated added cost of testing their beacon. They agreed and were included in the evaluation. The Techtest GPS PLB is a derivative of their 500-12 non-GPS military derived PLB/ELT to their latest build standard and not off-the-shelf. This should be taken into account in any comparison. This beacon was unique in offering a 243 MHz military homing frequency and two-way voice communications on 121.5/243 MHz.

In order to ensure that the consumer beacons tested were representative of those being purchased by consumers, West Marine supplied ACR and McMurdo beacons from their stock for the test, but expected to either be reimbursed by the Foundation or for these beacons to be replaced. Due to the prohibitively high cost of the beacons, even at wholesale approximately $18,500 for the ACR beacons and $17,500 for the McMurdo beacons, the manufacturers were offered the opportunity to participate in the evaluation in exchange for their providing the beacons to be tested. No matter their response, it was the organizers' intention to test the ACR and McMurdo beacons, and initial fundraising goals were based on the presumption that they would not participate and the beacons would have to be paid for.

Those manufacturers who elected to participate would be required by agreement to either provide beacons for testing (9 EPIRBs and 15 PLBs of each model to be tested) in the case of those not readily available in the U.S., Techtest being the only one, or to replace beacons already obtained from West Marine and sequestered by the Foundation, the case with ACR and McMurdo. An agreement with the Foundation was signed by all participating manufacturers outlining requirements and responsibilities of the parties.

Quoting Chris Hoffman, Technical Director of McMurdo, "I believe that the biggest stumbling block is the Personal Liability Waiver, with the Confidentiality Agreement being a secondary issue. I have spoken to our parent company and they still will not let us sign the waiver, I guess that USA and UK laws and liabilities, which I don't for a minute purport to understand, are different enough to create the problems. So how does this sound as a way forward, we have very nearly agreed the Main Agreement between us and are almost in a position where we would be happy to sign this, if we could sort out the last outstanding minor legal issue. However nobody from McMurdo would attend the trials as a witness as I am sure that you already have enough 'experts' and independent witnesses to cover anything that needs doing anyway. This then removes the issues with the Personal Liability Waiver and Confidentiality Agreement." The Foundation agreed to this proposal and McMurdo did not have a representative present for the tests. ACR and Techtest did send representatives.

Pursuant to the agreements with the manufacturers as another inducement to participate, these manufacturers have also be given a preview of the draft report and were invited to offer a response if desired.

Invitations were also sent out to numerous Search and Rescue-related organizations to particpate or serve as independent observers. NOAA sent a technical representative. The AFRCC originally agreed to send a representative, but canceled at the last minute, reportedly due to a scheduling conflict. While U.S. Coast Guard headquarters and the Office of Search and Rescue declined to participate, the U.S. Coast Guard Office of Aviation Engineering authorized the Aviation Life Support Equipment Manager and Aviation Life Support Prime Unit Manager to participate. FAA sent a technical representative.

Evaluation Limitations and Considerations

ACR representative re-codes an ACR GlobalFix EPIRB to test protocol code onsite with other attendees as witnesses

As with many evaluations of lifesaving equipment, this one has been subject to limitations imposed by financial constraints, time and practical safety considerations.

Ideally, it would be desirable to test multiple distress beacons of each model in each scenario. The larger sample size would serve to mitigate the effects of a random failure that might not be typical. The high cost of the distress beacons, particularly in view of the uncertainty as to whether beacon manufacturers would participate, and thus mitigate the purchase of the beacons at significant expense, made this approach prohibitive.

By the same token, it is generally accepted that lifesaving equipment must be exceptionally reliable. Because failure can be fatal, consumers have a reasonable expectation that lifesaving equipment will work the first time, every time. Lifesaving equipment failure is not considered an option by the consumer. As such, any beacon failure must be considered unacceptable and this mitigates the potential adverse effects of testing only a single distress beacon of each model in each scenario.

The time necessary to conduct the testing also limited the number of beacons that could be tested, as well as the number and scope of the scenarios to be evaluated. Time available also impacted the actual conduct of the testing when failure to acquire location more often than expected required on-scene modification of the testing in order to ensure completion within the available time. Additional time also translates to additional financial costs, not only for the evaluators, but also for the support personnel and organizations and the manufacturers who participated. The full week spent testing was the practical limit, and even then some participants had to cut their attendance short.

Re-coding of McMurdo Precision GPS EPIRB to test protocol code at the McMurdo factory. McMurdo rejected doing the re-coding onsite, necessitating shipment to and from the U.K.

Real world testing introduces numerous variables beyond the control of the evaluator. In the case of this evaluation, significant potential variables included weather, sea conditions, and GPS satellite visibility. All the manufacturers of the beacons tested signed on as participants, implicitly acknowledging that these variables were within accepted norms, and would not adversely impact the results if the evaluation were to be conducted in substantial accordance with the draft test protocols provided to them.

These distress beacons are meant to be used in extremis, often under the least favorable conditions of weather and, in the case of marine use, extreme sea conditions, often the cause for their necessary use by survivors. This evaluation was, for both practical and safety reasons, limited as to what tested environmental conditions could be experienced. Weather conditions were mild. Rainfall or exposure to drenching amounts of water in a marine environment was simulated for some scenarios, but was moderate, at worst, compared to what might conceivably be experienced under real life-threatening circumstances. Sea conditions varied from moderate, but unchallenging, at their worst to virtually dead flat seas at times, as noted in the scenario reports. Any failures must be viewed in this light, but the ultimate value of success in these tests must also be tempered by these limitations.

When reviewing the results presented here, care must be taken not to compare performance without consideration for the manifest differences between some beacons. Those beacons relying upon an external GPS source are fundamentally different in both operation and packaging to those having an internal GPS source. These differences must be taken into consideration when evaluating the performance of the beacons (they will be enumerated later on in this report).

The results presented here are for tests of particular beacons. Readers of this report are cautioned that due to the complex interactions involved, it can be potentially erroneous to extend the self-location results for any particular beacon to any beacons not tested. Any difference in GPS chip, software, GPS antenna and relationship between the GPS antenna and transmitting antenna could produce different results.

Summary of the Results

Doug Ritter (right), with FAA/CAMI representative Jerry McDown, sets up monitoring computers and receivers for Baseline phase of tests.

This evaluation of 406 MHz Location Protocol Beacons was limited in scope to three beacon manufacturers; ACR Electronics (Ft. Lauderdale, Florida, USA – a subsidiary of Chelton/Cobham PLC United Kingdom); McMurdo Ltd. (Portsmouth, United Kingdom – a subsidiary of Chemring Group PLC, United Kingdom); and Techtest Ltd. (Herefordshire, United Kingdom – a subsidiary of HR Smith Group, United Kingdom), who produce beacons approved for the U.S. market and which are also sold worldwide.

This evaluation was primarily concerned with the self-locating performance of these beacons in real-world conditions, as well as a limited specific set of other lesser issues, and not the beacons' performance vis-à-vis COSPAS-SARSAT or other regulatory standards, per se, nor for the most part any other specific performance parameters of the beacons except those few others specifically included.

Beacons were divided into types; EPIRB (Emergency Position Indicating Radio Beacon, a marine distress beacon) or PLB (Personal Locator Beacon for personal use on land or in the maritime environment), by whether they used an external GPS source or an internal GPS source for self-location, and by whether they were off-the-shelf consumer beacons or a military derived PLB/ELT (aviation Emergency Locator Transmitter). While no beacon tested performed flawlessly, there were clear distinctions in self-locating performance among beacons during the evaluations. All the beacons tested appear to provide the minimum acceptable level of distress alerting performance expected from conventional, non-location protocol 406 MHz emergency beacons.

Beacons for lab testing ready to go.

The following beacons were tested:

• ACR Electronics "RapidFix 406 MHz EPIRB" with GPS Interface, Model RLB-33 (external GPS), also sold by Northern Airborne Technology (NAT) under the brand name "GeoTrack 406 EPIRB"
• ACR Electronics "GlobalFix 406 MHz EPIRB" with Integral GPS, Model RLB-35 (internal GPS), also sold by Northern Airborne Technology (NAT) under the brand name "SatFind-406 Survival GEPIRB II"
• ACR Electronics "GyPSI 406 MHz PLB" with GPS Interface, Model PLB-100 (external GPS)
• McMurdo Ltd. "Precision 406 MHz GPS EPIRB" (internal GPS), also sold as the "G4 406 MHz GPS EPIRB"
• McMurdo Ltd. "Fastfind Plus 406 MHz Personal Location Beacon" or "Fastfind Plus 406 MHz PLB" (internal GPS)
• Techtest Ltd. Model 500-27 406 MHz GPS PLB with 121.5/243 MHz VHF 2-way voice communications (internal GPS)

Rainfall testing of McMurdo Fastfind Plus PLB in screen room during laboratory testing.

The beacons tested that do not have an internal GPS receiver are dependent upon an external GPS for self-location information. The reference GPS used for testing was a Garmin eTrex Legend, chosen because it is a WASS-enabled mid-range member of the most popular moderate priced portable handheld GPS line sold in the U.S. and because the manufacturer of the beacons tested, ACR Electronics, at various times has offered units from this line of handheld GPS as a package with their beacons, the ACR GyPSI 406 PLB and ACR SatFind 406 EPIRB. Our experience suggests that this GPS offers mediocre performance in comparison with better quality, and often more expensive, GPS receivers which were able to reliably acquire a location in circumstances when the Garmin eTrex did not.

(Please note that the terms "success" and "fail" in these tables refers to the acquisition of a GPS-derived location and is not indicative of the 406 MHz alerting performance of the beacons.)

Summary of Baseline Testing

Summary of Maritime Testing

Summary of Inland Testing

Recording number of satellites in view, signal strength and location just prior to activating the McMurdo Precision GPS EPIRB in the baseline tests.

The ACR and McMurdo beacons were literally off-the-shelf beacons from West Marine stock, taken from their warehouse and store shelves.

The beacons tested that do not have an internal GPS receiver are dependent upon an external GPS for self-location information. The reference GPS used for testing was a Garmin eTrex Legend, chosen because it is a WASS-enabled mid-range member of the most popular moderate priced portable handheld GPS line sold in the U.S. and because the manufacturer of the beacons tested, ACR Electronics, at various times has offered units from this line of handheld GPS as a package with their beacons, the ACR GyPSI 406 PLB and ACR SatFind 406 EPIRB. Our experience suggests that this GPS offers mediocre performance in comparison with better quality, and often more expensive, GPS receivers which were able to reliably acquire a location in circumstances when the Garmin eTrex did not. In these instances, had the beacons been interfaced with the better performing GPS, they would have been able to transmit a location. The self-locating performance of these beacons is entirely dependent upon the quality of the GPS chosen by the user for the interface.

In the case of beacons using an external GPS source, the external GPS was turned off and the activation sequence initiated by turning on the GPS co-located with the beacon. It was logistically impracticable to achieve a full cold start of the GPS, but this ensured that the GPS was not transmitting a location achieved under more favorable conditions than those of the beacons with integral GPS. The warm start would be a likely scenario for PLB use in the wilderness, as the GPS would be expected to have been used for navigation within a short period of time of its use to interface with the beacon. For external GPS EPIRBs mounted on a boat and permanently interfaced with the boat's GPS this would not be a factor at all. For a cold start using an external GPS, the typical cold start time to location acquisition can be derived experimentally or from the manufacturer. In the case of the Garmin eTrex Legend reference GPS used in this evaluation, this would add "up to 5 minutes" according the manufacturer's literature.

Coast Guard Rescue Swimmer uses fire hose to simulate rainfall on Techtest 500-27 GPS PLB

The evaluation revealed a marked difference in self-locating performance among the integral GPS beacons tested. The ACR GlobalFix 406 EPIRB and Techtest Model 500-27 PLB generally provided location information within a few minutes from activation under all but the most onerous scenarios tested, with a few exceptions.

By contrast, the McMurdo Fastfind 406 PLB and McMurdo Precision 406 GPS EPIRB generally failed to provide location information except under ideal conditions. Even in scenarios where there were strong signals from 4 or more GPS satellites, and often 6 or more, as shown on the Garmin eTrex GPS, these beacons failed to provide a location unless the sky view was virtually unimpeded over the full hemisphere and there was little or no movement of the beacon due to the motion of the water, in the case of the testing on and in the water. (In theory, a GPS receiver is capable of deriving a longitude and latitude with 3 satellites in view and locked on and all commercial units that the authors are familiar with will do so reliably.)

In the maritime testing, the McMurdo beacons failed to acquire a location in any of the planned test scenarios, effectively a total failure in the marine environment. The only acquisition, by the McMurdo Precision 406 GPS EPIRB, occurred when it was specially provided a unique opportunity under virtually ideal conditions with only the slightest swells and a glassy water surface.

In the baseline testing, the McMurdo Fastfind Plus PLB was the only integral GPS beacon that failed to acquire a new location after being moved, despite being provided an extra opportunity -- two 20-minute update cycles.

Measuring McMurdo Fastfind Plus PLB 121.5 MHz homing signal attenuation with base of antenna submerged

The self-locating performance of these McMurdo beacons during the evaluation appears to contrast sharply with expected performance based upon the advertising and promotion by the company for its products, although it does not necessarily follow that these beacons do not meet required regulatory specifications which may not have any relation to real-world use with regards to self-location performance. This issue of ineffective international standards with regards to self-location performance has been previously identified by U.S. government sponsored testing and is confirmed by the results of this evaluation.

The field test portion of the evaluation was divided into three distinct phases: Baseline, Maritime, and Inland, with the results summarized in the tables that follow:

Lab testing of battery life at the PLBs' minimum operating temperatures, -20°C/-4°F for the McMurdo Fastfind Plus and Techtest 500-27 and -40°C/-40°F for the ACR GyPSI exceeded the minimum required 24 hours by a notable margin.

Doug Ritter prepares to activate Techtest 500-27 GPS PLB on aft deck of SV Willow

In November of 2003 the U.S. Coast Guard issued a report reviewing issues raised about the McMurdo Fastfind PEPIRBs they had purchased for use by Coast Guard boat crewmembers. (PEPIRB stands for Personal EPIRB, the designation given their version of the Fastfind PLB, which is coded as an EPIRB, not a PLB, and which is functionally the same as the Fastfind PLB, including the design of its antenna and antenna storage. It is not equipped with an integral GPS receiver) While the general contents of this report have been widely known, it was not until shortly prior to publication of this report that a copy of the Coast Guard's test plan and report was secured by the Foundation via a Freedom Of Information Act request. (Link to report opens a new browser window. Download a free PDF Reader)

The Coast Guard noted in its test plan that their studies "indicated that the beacons radiated power is extremely degraded by the presence of water in the antenna well." This conforms to our laboratory test findings in this regard. They conducted field tests to ascertain if this impacted the effectiveness of the beacons to provide an alert and Doppler derived location under operational conditions. Among the "lessons learned" presented in their report was that "when any amount of water is allowed to collect in the antenna storage well the signal is degraded and may prevent the COSPAS/SARSAT system from receiving the transmitted signal. After activation, boat crew members shall make every effort to keep the PEPIRB out of the water, the antenna and antenna storage well as dry as possible and the PEPIRB oriented so that the antenna has an unobstructed view of the sky." This conforms to our Conclusions and Recommendations in this regard (see Conclusion #7 and Recommendation #12).

Conclusions

BoatU.S. Foundation President Ruth Woods looks on as Coast Guard Rescue Swimmers simulate rainfall/ocean spray on ACR GlobalFix EPIRB

The authors of this evaluation are of the opinion that the following conclusions can be drawn from the data and experience collected during this evaluation, and general observations of the use of these beacons during this evaluation:

1. The self-locating performance deficits of some location protocol distress beacons that this evaluation has documented should not be interpreted as an indictment in any manner of the COSPAS-SARSAT Satellite Distress Alerting System or 406 MHz distress beacons in general. This system has proven to be an extremely reliable and effective means of distress alerting that has saved thousands of lives worldwide since its inception. Even if some of the beacons evaluated in this report have not reliably provided self-location data, they appear to provide the minimum acceptable level of distress alerting and Doppler locating performance expected from conventional, non-location protocol 406 MHz emergency beacons.
    
   
2. Assuming that all the beacons in this evaluation conformed to COSPAS-SARSAT specifications as represented, it appears self-evident that the COSPAS-SARSAT standards covering location performance of location protocol beacons with integral location means do not adequately predict the performance of these location protocol beacons in the real world.
    
   

3. Inland testing in "small" forest clearing

   Based on the test results, which proved to be consistent with previous de-identified testing conducted by the U.S. government at which the principal author was present, users of the McMurdo self-locating beacons tested may expect to find that GPS-derived location may not be transmitted unless environmental conditions are generally benign and the beacon is stable, and unless there is a largely uninterrupted sky view covering most of 180 degrees above and 360 degrees around the beacon location. This level of performance appears to be inconsistent with that portrayed in McMurdo's advertising and product literature and consumers' reasonable expectations.
    
   
4. Based on the test results, users of the ACR and Techtest self-locating beacons tested may expect to find that under most moderate environmental conditions a GPS-derived location will be reliably transmitted.
    
   
5. Consumer expectations regarding the performance of integral GPS beacons may be shaped by their personal experience with handheld GPS receivers, which can prove to be an unreliable comparison. Users of the popular-priced Garmin eTtrex class of GPS receivers can expect the ACR beacons to perform comparably, meeting their experiential expectations. They can expect that the Techtest beacon will perform comparably in all but the most challenging circumstances. However, McMurdo beacons are likely to fail to acquire a location in circumstances where the Garmin eTrex class GPS typically provides a location, but with only a minimum number of satellites in view and locked on (3 or 4 satellites). None of the beacons tested are likely to reliably acquire a location when a higher performance GPS receiver, such as the Garmin 12 or Garmin V, acquires a location with only 3 satellites in view and locked on. A consumer's experience using this class of handheld GPS is less likely to be indicative of a beacon's acquisition performance.
    
   

6. Inland testing in large meadow, self-test of McMurdo Fastfind Plus PLB.

   Location performance of beacons relying upon an external GPS source is entirely dependent upon the performance of that external source. With these beacons, if the external GPS gains a location, it will be transmitted. The evaluation showed marked differences in performance between handheld GPS receivers. In every instance where the standard reference external Garmin eTrex GPS source failed to acquire a location, had the beacon been interfaced with the better GPS on hand, they would have been able to transmit a location.
    
   
7. PLBs with blade antennas appear to provide significantly compromised 121.5 MHz performance when the base of the antenna is submerged in water. In situations where this occurs for an extended period of time while a direction finding (DF) search is in process, the beacon may not provide a useable signal for homing purposes under such circumstances.
    
   
8. On the basis of the laboratory tests, submerging the base of the PLBs' antenna in water appears to result in orders of magnitude attenuation of the 406 MHz signal. This could compromise the ability of the PLB to reach the COSPAS-SARSAT geostationary satellite. In the maritime field test of this condition, only the Techtest with its conventional 50 ohm telescoping antenna transmitted an alert to the COSPAS-SARSAT geostationary satellite (no GPS location was acquired nor was one expected because the GPS antenna was submerged). It is postulated that this attenuation under these conditions could potentially be a factor in preventing transmission to the COSPAS-SARSAT geostationary satellites and especially so in circumstances where environmental conditions are more detrimental to RF transmissions. It is postulated that this would not be expected to prevent transmission to the low earth orbit satellites under any likely circumstances where they would otherwise be successfully received.
    
   

9. McMurdo Fastfind PLB antenna storage well with retained water

   A design such as that used in the McMurdo Fastfind that can retain water at the base of the antenna appears to compromise the performance of the antenna when that occurs, but based on the limited capability laboratory tests conducted it does not appear to attenuate the performance to the extent that complete submersion does, provided the beacon is otherwise kept dry. In the maritime field tests under these conditions, (antenna well filled) the Fastfind was able to communicate an alert to the COSPAS-SARSAT geostationary satellite (no location was acquired in this test). It is postulated that this attenuation under these conditions (antenna well filled) could potentially be a factor in preventing transmission to the COSPAS-SARSAT geostationary satellites in circumstances where environmental conditions are more detrimental to RF transmissions. It is postulated that this would not be expected to prevent transmission to the low earth orbit satellites under any likely circumstances where they would otherwise be successfully received.
    
   
10. Results from the gorge test suggests that Doppler location can be achieved even with a very limited sky view, though it may take multiple LEO satellite passes. Further investigation to establish practical limits is worthy of consideration.
     
    
11. Should the PLB be tipped over such that the antenna is oriented in an abnormal position instead of the nominal vertical position, there appears to be minimal impact on the capability of the beacon to communicate with the COSPAS-SARSAT geostationary satellite.