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An emergency locator transmitter (ELT) is an independent battery powered transmitter activated by the excessive G-forces experienced during a crash. It transmits a digital signal every 50 seconds on a frequency of 406.025 MHz at 5 watts for at least 24 hours. The signal is received anywhere in the world by satellites in the COSPAS-SARSAT satellite system. Two types of satellites, low earth orbiting (LEOSATs) and geostationary satellites (GEOSATs) are used with different, complimentary capability. The signal is partially processed and stored in the satellites and then relayed to ground stations known as local user terminals (LUTs). Further deciphering of a signal takes place at the LUTs, and appropriate search and rescue operations are notified through mission control centers (MCCs) set up for this purpose. NOTE: Maritime vessel emergency locating beacons (EPIRBs) and personal locator beacons (PLBs) use the exact same system. The United States portion of the COSPAS-SARSAT system is maintained and operated by NOAA. Figure 1 illustrates the basic components in the COSPAS-SARSAT system. ELTs are required to be installed in aircraft according to FAR 91.207. This encompasses most general aviation aircraft not operating under Parts 135 or 121. ELTs must be inspected within 12 months of previous inspection for proper installation, battery corrosion, operation of the controls and crash sensor, and the presence of a sufficient signal at the antenna. Built-in test equipment facilitates testing without transmission of an emergency signal. The remainder of the inspection is visual. Technicians are cautioned to not activate the ELT and transmit an emergency distress signal. Inspection must be recorded in maintenance records including the new expiration date of the battery. This must also be recorded on the outside of the ELT. Use of Doppler technology enables the origin of the 406 MHz ELT signal to be calculated within 2 to 5 kilometers. Second generation 406 MHz ELT digital signals are loaded with GPS location coordinates from a receiver inside the ELT unit or integrated from an outside unit. This reduces the location accuracy of the crash site to within 100 meters. The digital signal is also loaded with unique registration information. It identifies the aircraft, the owner, and contact information, etc. When a signal is received, this is used to immediately research the validity of the alert to ensure it is a true emergency transmission so that rescue resources are not deployed needlessly. ELTs with automatic G-force activation mounted in aircraft are easily removable. They often contain a portable antenna so that crash victims may leave the site and carry the operating ELT with them. A flight deck mounted panel is required to alert the pilot if the ELT is activated. It also allows the ELT to be armed, tested, and manually activated if needed. [Figure 3] Modern ELTs may also transmit a signal on 121.5 MHz. This is an analog transmission that can be used for homing. Prior to 2009, 121.5 MHz was a worldwide emergency frequency monitored by the CORPAS-SARSAT satellites. However, it has been replaced by the 406 MHz standard. Transmission on 121.5 MHz are no longer received and relayed via satellite.The use of a 406 MHz ELT has not been mandated by the FAA. An older 121.5 MHz ELT satisfies the requirements of FAR Part 91.207 in all except new aircraft. Thousands of aircraft registered in the United States remain equipped with ELTs that transmit a .75 watt analog 121.5 MHz emergency signal when activated. The 121.5 MHz frequency is still an active emergency frequency and is monitored by over-flying aircraft and control towers.Technicians are required to perform an inspection/test of 121.5 MHz ELTs within 12 months of the previous one and inspect for the same integrity as required for the 406MHz ELTs mentioned above. However, older ELTs often lack the built-in test circuitry of modern ELTs certified to TSO C-126. Therefore, a true operational test may include activating the signal. This can be done by removing the antenna and installing a dummy load. Any activation of an ELT signal is required to only be done between the top of each hour and 5 minutes after the hour. The duration of activation must be no longer than three audible sweeps. Contact of the local control tower or flight service station before testing is recommended.It must be noted that older 121.5 MHz analog signal ELTs often also transmit an emergency signal on a frequency of 243.0 MHz. This has long been the military emergency frequency. Its use is being phased out in favor of digital ELT signals and satellite monitoring. Improvements in coverage, location accuracy, identification of false alerts, and shortened response times are so significant with 406 MHz ELTs, they are currently the service standard worldwide. RELATED POSTS ELTs are emergency transmitters that are carried aboard most general aviation aircraft in the U.S. In the event of an aircraft accident, these devices are designed to transmit a distress signal on 121.5 and 243.0 MHz frequencies, and for newer ELTs, on 406 MHz. ELTs are required to be installed in almost all U.S.-registered civil aircraft, including general aviation aircraft, as a result of a congressional mandate. The mandate resulted from the 1972 loss of U.S. Representative Hale Boggs and Nick Begich in Alaska after their aircraft crashed and was never found. When ELTs were mandated in 1973, most GA aircraft were equipped with an ELT that transmits on the 121.5 MHz frequency, the designated international distress frequency. The original ELTs were manufactured to the specifications of an FAA technical standard order (TSO-C91). Historically, these ELT’s have experienced an activation rate of less than 25 percent in actual crashes and a 97 percent false-alarm rate. In 1985, a new TSO-C91A ELT was developed, which substantially reduces or eliminates many problems with the earlier model. The TSO-C91A provides improved performance and reliability (with an activation rate of 73 percent in actual crashes) at a reasonable cost to users. Since then, an even more advanced model of ELT has been developed — the TSO-C126 ELT (406 MHz). This newest model activates 81-83 percent of the time and transmits a more accurate and near-instantaneous emergency signal by utilizing digital technology. This digital 406 MHz ELT also allows search and rescue personnel to have vital information specific to you and your aircraft.  ELTs were originally intended for use on the 121.5 MHz frequency to alert air traffic control and aircraft monitoring the frequency. In 1982, a satellite-based monitoring system was implemented, COSPAS-SARSAT, to provide a better way to detect these distress signals. In 2009, the international COSPAS-SARSAT satellite system discontinued satellite-based monitoring of the 121.5/243 MHz frequencies, in part because of a high number of false signals attributed with these frequencies. Satellite monitoring today utilizes the 406 MHz frequency only. While there's no requirement in the United States to replace the first- and second-generation 121.5 MHz ELTs, since 2009, 121.5 and 243 MHz distress signals transmitted from ELTs operating on the lower frequency have only been able to be detected by ground-based receivers, such as local airport facilities and air traffic control facilities, or by overflying aircraft. Pilots should be aware that existing 121.5 MHz ELTs, although still legal from the FAA's perspective, will provide extremely limited assistance if an aircraft crashes, especially in a remote location. In 2019, the manufacture, importation, or sale of 121.5 MHz ELTs became prohibited in the United States per an FCC final rule, but the new rule does not prohibit aircraft operators from continuing to use 121.5-MHz ELTs now installed in aircraft, nor does it cut off the availability of batteries or other replacement parts. Impact of False AlertsThe Air Force Rescue Coordination Center (AFRCC) is responsible for coordinating search and rescue activities in the 48 contiguous United States and will support search and rescue operations for American citizens in Mexico and Canada. This agency is alerted to an ELT activation and determines an appropriate response, sometimes resulting in Civil Air Patrol, United States Coast Guard, and other first responders initiating a search. The AFRCC can be reached at 1-800-851-3051. In 2017, there were 8,898 406 MHz ELT activations in the AFRCC area of responsibility and about 98% of those alerts were false alarms. Just 122 of the alerts in 2017 were actual distress cases. For each false alert, AFRCC specialists put in considerable research and manhours to track down the ELT and owner. Each activation is treated as an emergency so each false alert is a distraction and negatively affects other search and rescue missions. About 90% of false alerts occur because of beacon mishandling during the testing and maintenance of these systems. Whether utilizing a 121.5 MHz or 406 MHz ELT, owners should be familiar with the guidance in the Aeronautical Information Manual and the ELT Advisory Circular as far as preventing false alerts and conducting ELT testing in a responsible way. It is also a legal requirement for owners of a 406 MHz ELT to register their ELT to allow a faster response to an ELT activation. Additional information can be found in a July 2, 2018, Information for Operators notice from the FAA. Good practice for all pilots is to monitor 121.5 MHz when flying and prior to shutting down the aircraft as any activation of a 121.5 MHz ELT, such as due to a hard landing, will be immediately evident. AOPA's Position on 406 MHz MandateAOPA supports the installation of these more advanced ELTs on a voluntary basis. General aviation is an industry already struggling under the weight of increased regulation and mandated equipage, and the decisions to replace an existing ELT should be left to the discretion of the aircraft owner. Therefore, AOPA does not support any attempt to mandate or otherwise require the replacement of existing 121.5/243 MHz ELTs with 406 MHz units. However, the association does support the education of pilots and aircraft owners as to the limits of 121.5/243 MHz ELTs and the benefits of 406 MHz units. The benefits of advanced ELTs must be balanced against cost and the needs of the individual aircraft owner. An individual owner may opt to invest in accident prevention technology, such as Non Required Safety Enhancing Equipment (NORSEE) versus spending the same money on a 406 MHz ELT, which is only effective once an accident has occurred. New Technologies offer Alternate SolutionsWhile ELT technology and certification has evolved slowly over the years, new technologies that utilize satellite communication networks have made products available that are designed for both tracking and distress alerting. Devices such as SPOT and Garmin Inreach provide tracking and distress alerting, but must be manually activated. Other systems, such as Spidertracks, provide automated alerting which is triggered if the tracking signal stops without proper shut-down notification. In the latter case, the loss of signal from an aircraft crash or mishap would trigger the distress call, rendering the issues of the system’s post-crash survivability and activation a moot point. While these devices are not certified by the FAA, or replace the legal requirement for an ELT, aircraft owners may want to investigate them as a safety enhancement in place of equipping with a 406 MHz ELT. The FAA has developed programs, such as the Enhanced Special Reporting Service (eSRS) which links certain devices to Flight Plans in Alaska. Adverse Condition Alerting Service (ACAS) offered by Leidos Flight Service provides a slightly different set of services, based on satellite tracking devices. AOPA continues to monitor these technologies and services, which someday may lead to additional options for aircraft owners to meet FAA requirements, in the most cost effective manner possible. International RequirementsThe International Civil Aviation Organization (ICAO) standard is the 406 MHz ELT, which is mandatory in many countries for general and commercial aviation. Pilots should check the ELT requirement for any country they will be flying to or over. At this time, Canada requires an ELT that can transmit a signal on 121.5 MHz, and they highly recommend an ELT that can transmit over 121.5 MHz and 406 MHz. Mexico’s deadline for 406 Mhz ELTs on piston-powered private aircraft with a maximum takeoff weight of less than 12,566 lbs is June 30, 2018. |
When activated an emergency locator transmitter ELT transmits on a 118.0 MHz B 123.0 MHz C 406 MHz?
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