121.5 Phase-Out

Switch to 406!

The International Cospas-Sarsat System has ceased satellite processing of 121.5/243 MHz beacons on 1 February 2009. All beacon owners and users should replace their 121.5/243 MHz beacons with 406 MHz beacons as soon as possible.

Only 406 MHz beacons are now detected by the Cospas-Sarsat satellite system. This affects all maritime beacons (EPIRBs), all aviation beacons (ELTs) and all personal beacons (PLBs). However, other devices (such as man overboard systems and homing transmitters) that operate at 121.5 MHz and do not rely on satellite detection are not affected by the phase-out of satellite processing at 121.5 MHz.

The decision to terminate 121.5/243 MHz processing was made in October 2000 at the 25th Session of the Cospas-Sarsat Council (CSC-25).


Why Switch?

Cospas-Sarsat made the decision to cease satellite processing at 121.5/243 MHz in response to guidance from the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO). These United Nations organizations mandate safety requirements for aircraft and maritime vessels and have recognised the limitations of the 121.5/243 MHz beacons and the superior capabilities of the 406 MHz alerting system.

The digital 406 MHz beacons offer many advantages over analog 121.5/243 MHz beacons. With a 406 MHz beacon, the position of the distress can be relayed to rescue services more quickly, more reliably and with greater accuracy.

  406 MHz Beacon 121.5/243 MHz Beacon
Signal Digital: unique identification, registration data provides information on the owner/vessel or aircraft Analog: no data encoded, higher false alert rate
Signal Power 5 Watts pulse 0.1 Watts continuous (typical)
Coverage Global Regional
Position Accuracy Within 5 km (Doppler), 100m if GNSS (GPS) position is encoded in message Within 20 km (Doppler only)
Alert Time GEO alert within 5 minutes Waiting time for LEO satellite pass 45 minutes average
Doppler Position Ambiguity Resolution possible at first satellite pass Two passes required to resolve position ambiguity

With a 121.5/243 MHz beacon, only one alert out of every 50 alerts was a genuine distress situation. This had a significant effect on the resources of search and rescue (SAR) services. With 406 MHz beacons, false alerts have been considerably reduced (about one alert in 17 is genuine) and when properly registered can normally be resolved with a telephone call to the beacon owner using the encoded beacon identification. Consequently, real alerts can receive the attention they deserve.

When a 406 MHz beacon signal is received, SAR authorities can retrieve information from a registration database. This includes beacon owner contact information, emergency contact information, and vessel/aircraft identifying characteristics. Having this information allows SAR services to respond appropriately. Make sure your 406 MHz beacon is properly and accurately registered! 


For more information

For the detailed Cospas-Sarsat Phase Out Plan for 121.5/243 MHz Satellite Alerting Service, please see document
C/S R.010 "Cospas-Sarsat Phase-Out Plan for 121.5/243 MHz Satellite Alerting.


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