Back in February 2009, the Cospas-Sarsat System which is a satellite based search and rescue (SAR) distress alert detection and information distribution system, established by Canada, France, the United States, and the former Soviet Union in 1979, stopped processing signals from 121.5 MHz and 243 MHz beacons. Cospas-Sarsat is best known as the system that detects and locates emergency beacons activated by aircraft, ships and backcountry hikers in distress. Over the years many countries have joined the project, either as providers of ground segments or as user states. Cospas-Sarsat is based in Montréal, Québec, Canada.

At present Cospas-Sarsat only monitors signals from 406 MHz beacons. The idea was to reduce SAR resources on false alerts while simultaneously increasing the responsiveness of the system for real distress cases. As a result “the public interest” the Federal Communications Commission (FCC) proposed to prohibit the further certification, manufacture, importation, sale, or use of 121.5 MHz ELTs. The Commission acknowledged that aircraft owners and pilots still using 121.5 MHz ELTs would incur an expense, but concluded that the safety benefits outweighed the compliance cost, especially given that the aviation community had been on notice since 2000 that Cospas-Sarsat would cease monitoring the frequency.

Prior to the founding of Cospas-Sarsat, the civilian aviation community had already been using the 121.5 MHz frequency in the VHF band for distress, while the military aviation community utilized 243.0 MHz in the UHF band as the primary distress frequency with 121.5 MHz in the VHF band as the alternate.