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Emergency Locator Transmitters (ELTs)

Source: October 2000 Civil Air Patrol News

Mandatory ELT Laws Instituted in January 1968 –

A long article appeared in the Saturday Evening Post about the death of 16-year-old Carla Corbus. Shortly afterward on Capitol Hill, Colorado Sen. Peter Dominick talked about the diary she left in the margins of an airman's guide. She and her mother, badly injured, survived an airplane crash in the Trinity Alps of California in March 1967, only to starve to death after more than 54 days. For weeks, Carla heard search planes through the snow and rain. She heard up to 59 scheduled airliners fly overhead every day. The senator demanded a law mandating aircraft emergency beacons to save lives and reduce suffering by shortening search time. The next year, both houses of Congress passed a mandatory aviation emergency beacon law sponsored by Dominick, but it was inadvertently left out of the bill sent to the president for signing.

California had had enough long and unsuccessful searches, which had cost the lives of many searchers and crash victims waiting for a rescue. The winter 1969 search for the "Gamblers' Special" DC-3 in the Sierra Nevada Mountains had three search aircraft crashes, which claimed two lives and injured eight. The state was unwilling to wait for a federal ELT law. In autumn 1969, it passed a mandatory "downed aircraft locator" law with a two-year phase-in period for most aircraft based in California. Just before that, Washington had passed a similar law requiring "downed aircraft rescue transmitters" on air taxi and charter aircraft. New Hampshire, Colorado and New Mexico legislatures started to propose mandatory locator beacon state laws as well.

In summer 1970, Dominick, assisted by Washington Sen. Warren Magnuson, sponsored a mandatory ELT bill which was signed into law by President Nixon on Dec. 29, 1970, as a last-minute rider to the Occupational Safety and Health Act. It required most general aviation aircraft to install ELTs by Dec. 30, 1973, and it preempted all the state ELT laws. The federal ELT law left the matter of alerting vague, although the initial idea was alerting by over flying aircraft which could receive an ELT's 75-milliwatt signal from 50 nautical miles away. Many tried to get airlines to listen voluntarily for activated ELTs on 121.5 MHz, just as most seagoing vessels must monitor an emergency frequency and respond to mayday calls. Only two airlines, Air West and National Airlines, agreed to constant monitoring, while most agreed only to monitor, if requested, by air traffic control. The idea of constant airliner alerting died.

On Oct. 16, 1972, House majority leader Hale Boggs of Louisiana, Congressman Nick Begich of Alaska, pilot Don Jonz, and Russ Brown, a Begich aide, turned up missing on a flight from Anchorage to Juneau, Alaska, in a Cessna 310. Despite one of the longest searches in American history, they have never been found. The failed search cemented in Congress the value of a mandatory ELT law. As the mandatory installation date approached, the FAA and Congress realized there were not enough beacons for sale. The installation date was slipped to June 30, 1974. In 1975, aircraft owners appealed to Congress for relief from part of the ELT law since thousands of ELTs in use were found to be defective, replacement parts were scarce and the FAA interpreted the law such that an aircraft was not airworthy without a working ELT. About 20,000 aircraft were grounded waiting for a replacement ELT due to one manufacturer's design defect and another 15,000 were waiting up to a month for new ELT batteries for another defective model. Congress passed a law in 1977 allowing limited use of aircraft without a working ELT.

How Do ELTs Work?

ELTs are designed to activate automatically when a specific amount of gravity (5Gs) closes a switch after a very hard impact, compared to emergency position indicating radio beacons for boats which automatically activate when the EPIRB reaches a certain depth or contacts water. The FAA responded to the defective early ELTs by outlawing the installation of C-91 ELTs and certifying C­91a ELTs with an improved gravity switch, improved crash and fire-worthy casing, and batteries that work in colder temperatures. The FAA does not currently require that the already installed C-91 beacons be replaced with newer models, until they fail to operate correctly.

More False Alerts a Continuing Problem

In 1982, the Soviet Union launched the first satellite designed to repeat 121.5/243 MHz signals from ELTs and EPIRBs. The next year, the United States launched a similar satellite. In 1988, with enough search and rescue satellites in orbit, the United States, the Soviet Union, France and Canada signed the International Cospas-Sarsat Program Agreement to manage the satellite alerting system for emergency beacons. CAP members faced an increasing number of false alerts from the new satellite alerts. The problem was so bad that NOAA, which flies the American satellites with the 121.5/243 MHz repeaters, started a national advertising campaign to reduce false alerts. Posters advising, "Don't cry wolf” began appearing at many American airports. The Alaska Wing and the FAA ran a free ELT testing program and found a large number of defective and improperly installed ELTs.

By the early 1990s, it was clear the education campaign to reduce ELT false alerts was not working. The FAA impaneled a group of experts from federal agencies, CAP, AOPA and EAA to draft new ELT regulations. The panel did a large amount of work to agree on specifications for the new digital TSO C-126 406 MHz ELTs. However, in February 1995, it deadlocked on the issue of when, if ever, to mandate the replacement of the C-91 ELTs, with the agencies voting for a mandatory retrofit to TSO C-126, while all the others voted for a choice of C-91a or C-126 retrofit. About the same time, Cospas-Sarsat's 32-nation membership began discussing the problem that C-91 and C-91a beacons were never intended for satellite alerting, and their false alerts were overwhelming search forces. For example, the United States now receives more than 100,000 satellite alerts every year and thus cannot possibly respond to them all.

It is official U.S. Coast Guard and Air Force policy to wait to react to a 121.5 MHz emergency signal until there have been at least two to three polar satellite passes over a signal, which usually takes two or more hours, unless there has been a report of a missing aircraft, vessel or a person with a personal locator beacon, in which case search forces are alerted quicker to satellite alerts. This search-response delay is the exact opposite of the SAR response Dominick had intended when he sponsored the mandatory ELT law. His intent was to reduce the suffering of crash victims and to save lives with quicker searches. 121.5/243 MHz Phase-out Over the past three years, the many nations and international organizations which influence search and rescue matters have been deciding what to do with the false alert issue. Russia decided unilaterally to stop launching satellites with 121.5/243 MHz repeaters by 2006.

Recommendation to “Phase Out” 121.5/243 MHz

In June 2000, all the Cospas­-Sarsat nations recommended the "phase-out" of 121.5/243 MHz satellite alerting by Feb. 1, 2009. This recommendation was expected to be formally adopted by the Cospas-Sarsat Council in October 2000. "Phase-out" means 121.5/243 MHz beacons will no longer be detected by satellites, but it does not mean ELTs and EPIRBs will no longer use either frequency. Some countries, such as Venezuela, already do not respond to 121.5 MHz signals unless there is a report of a missing aircraft or vessel. The FCC, at the request of the U.S. Coast Guard this year, is implementing regulations that will remove the certification for the manufacture and sale of 121.5 MHz EPIRBs in the United States by 2004, and by the end of 2006 forbid their use. The FAA's current policy on 406 MHz ELTs is their use will not become mandatory.406 MHz Beacons Key parts of the phase-out are the new 406 MHz ELTs and EPIRBs. These beacons are designed for satellite alerting. When activated, they transmit a 5-watt digital burst every 50 seconds. The burst has an encoded individual beacon identifier used by national authorities to track down the beacon owner by telephone to avoid alerting and launching search forces for false alerts. American aircraft and boat owners with 406 MHz beacons who fail to register them or fail to affix a current NOAA registry decal to their beacons can face penalties from the FCC, FAA and/or U.S. Coast Guard, but to date no fines have been assessed. The encoded burst also prevents the problem of 121.5 MHz non-beacon alerts triggered by non-beacon devices such as pizza ovens, printer networks, and copiers, since those things cannot produce the digital burst. If a 406 MHz beacon has an internal GPS receiver or has a "nav interface," the digital burst includes the latitude and longitude of the beacon, which provides instant distress-location information. In addition to the digital burst, all 406 MHz beacons transmit continuously on 121.5 MHz for close-in homing by search forces. Therefore, search forces like CAP can continue to use 121.5 or 243 MHz direction-finding equipment and techniques. Instead of the current satellite alerting for the strictly 121.51/243 MHz beacons by the polar orbiting constellation, which may take hours to have its first satellite pass over a broadcasting beacon, satellite alerting with 406 MHz beacons is instantaneous.

The Cospas-Sarsat constellation started to include geostationary satellites with 406 MHz repeaters about 6 years ago. Unless a beacon has a "nav interface," polar satellites are still needed to determine a 406 MHz beacon position after an alert from a geostationary satellite. With one polar satellite pass, due to the greater frequency stability and power of the 406 MHz signals compared to the 121.5/243 MHz signals, the average satellite positioning accuracy for 406 MHz signals is less than 100 yards with "nav interface", or 1-3 nautical miles without the interface, compared to 12-16 nautical miles for C-91 and C-91a beacons.


By 2006, search forces should notice they no longer get daily missions to look for 121.5/ 243 MHz EPIRBs from satellite alerting, and by 2009 the same will be true for strictly 121.5/243 MHz ELTs. It is uncertain now what will happen after 2009 for C-91 and C-91a ELT search responses. Perhaps in a fittingly ironic reaction to the alerting phase out, CAP members may soon be dusting off their search skills from the 1970s to locate beacons from vague pilot reports which were common before the Cospas-Sarsat satellites were launched, if the FAA does not mandate a retrofit or removal of all old ELTs.