Emergency Locator Transmitters (ELTs) are emergency transmitters required to be installed on most U.S. aircraft. These transmitters are intented to assist search and rescue personnel find aircraft in the event of an accident. They are automatically activated in an accident by a “G” switch. A hard landing, and sometimes a not so hard landing, can also activate the ELT, so you should always monitor 121.5 before shut down.
ELTs were mandated in 1973. All early ELTs transmitted an analog emergency signal on 121.5 MHz frequency. Use of this frequency and technology had significant drawbacks in terms of facilitating the location and rescue of downed airman, and in recent years, ELTs which operate on the 406MHz frequency have become available. These improved ELTs transmit a more powerful digital signal and provide a much more accurate location. They also still include a 121.5 MHz signal for homing purposes since most Search and Rescue DF equipment still operate on 121.5 MHz.
For a comparison of 121.5 and 406 MHz ELTs, see: http://www.equipped.org/406_vs_1215.htm
406 MHz ELTs are expected to gain wider acceptance as both OEM and retrofit equipment in general aviation aircraft. The SR-22 G3 now includes a 406 MHz ELT as standard equipment.
The monitoring of 121.5 MHz frequencies by the COSPAS-SARSAT satellite system will be discontinued as of February 1, 2009. Once the satellite monitoring of 121.5 MHz frequencies is discontinued, ELTs operating on the 121.5 MHz frequency will provide little value to accident aircraft or survivors. Simply put, there is a good chance no one will hear the signal and it will need to be reported by a passing aircraft or a nearby ATC facility that monitors 121.5 MHz. Even then, the location is not provided and a time consuming search will need to be conducted.
Some aviators are electing to replace their 121.5 MHz ELTs with an upgraded 406 MHz ELT. Generally, an upgrade to a 406 MHz ELT costs between $1,500 and $2,500 depending on the unit selected and installation costs. An alternative to this is to carry a 406 MHz Personal Locator Beacon (PLB). While A PLB does not have the automatic activation feature of an ELT, it is far more reliable.
You can register your U.S. ELT at http://www.beaconregistration.noaa.gov NOAA is discontinuing sending out a Registration Decal after you register your ELT as it served no useful purpose. If you happen to receive one of these decals as they phase them out, you can just throw it away.