ARRLWeb: ARRL NEWS: Distress Beacons at 121.5 and 243 MHz Phased Out

This graphic gives an overview of how the Cospas-Sarsat system works. First, a beacon is activated due to grave or imminent danger (1). Next, the Cospas-Sarsat satellite systems receives the distress signal (2). The alert is re-transmitted to automated ground stations called Local User Terminals (LUTs) (3). Mission Control Centers (MCCs) receive the alerts from the LUTs and process the signals and them forward them to the Rescue Coordination Center (RCC) (4). The RCC verifies the distress and alerts the nearest Search and Rescue unit (5). The Search and Rescue unit goes to the distress scene (6).

As of February 1, the Cospas-Sarsat (Search and Rescue Satellite Aided Tracking) satellites are no longer monitoring distress beacons at 121.5 and 243 MHz. All mariners, aviators and individuals who use emergency beacons on those frequencies will need to switch to the newer, digital 406 MHz frequency if they want to be detected by the monitoring satellites. The National Oceanic and Atmospheric Administration (NOAA) claims that in 2008, beacons monitored by the Cospas-Sarsat worldwide system were responsible for almost 300 lives saved, including 203 people rescued in 65 in at-sea incidents and 12 people rescued in 7 aviation incidents.

"Over the years, many amateurs have played vital roles by monitoring frequencies that the satellites have stopped tracking," said ARRL Emergency Preparedness and Response Manager Dennis Dura, K2DCD. "While the switchover to 406 MHz just occurred, there is still 'older' equipment out in the world, so amateurs may want to continue monitoring, as they may save a person's life who doesn't have the latest gear, but is in distress and needs to be found."

According to NOAA's National Environmental Satellite, Data and Information Service (NESDIS), NOAA, the US Coast Guard, the US Air Force and NASA monitored these emergency beacons. According to NESDIS, problems in the frequency band that inundated search and rescue authorities with poor accuracy, as well as numerous false alerts that adversely impacted the effectiveness of lifesaving services, were some of the deciding factors to stop the monitoring of 121.5 and 243 MHz. The agency also acknowledged that two United Nations agencies -- the International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO) -- recommended the switchover to the 406 MHz digital frequency, even though the beacons for this frequency will cost more.

Cospas-Sarsat provides a satellite based worldwide monitoring system that detects and locates distress signals transmitted by 406 MHz Emergency Locator Transmitters (ELTs, used in aviation), Emergency Position Indicating Radio Beacons (EPIRBs, used for maritime) and Personal Locator Beacons (PLBs, used by individuals). The system includes space and ground segments that process the signals received from the beacon source and forwards the distress alert data to the appropriate Rescue Coordination Center (RCC) for action.

NOAA said that the 406 MHz emergency beacons have "superior performance capabilities" as compared to the 121.5 and 243 MHz beacons, as they "transmit a stronger signal and are more accurate, verifiable and traceable," and that the 406 MHz distress signals can be "easily detected within a matter of minutes. Each 406 MHz beacon has a unique ID encoded within its signal. As long as the beacon has been registered (required by law), RCCs can quickly confirm that the distress is real, who they are looking for and where they should look. This means that a search can be launched even before a final distress location has been determined. Position accuracy means the search area is less than 2 nautical miles in radius, which decreases the amount of time SAR teams must search."