Emergency Locator Transmitters (2024)

Emergency Locator Transmitters (1)

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 experiencedan 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 are mounted aft in the airplane, and designed to be triggered upon impact or may be manually activated using the remote switch and control panel indicator in the co*ckpit. Activation of the ELT triggers an audio alert, and 406-MHz ELTs transmit GPS position for search and rescue.

Emergency Locator Transmitters (2)

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 detectthese 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 Alerts

The 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 inMexico 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.

False Alert

The Civil Air Patrol and other government agencies have been trying to increase aviator’s knowledge on how to prevent an ELT false alert.

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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 Mandate

AOPA 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 Solutions

While 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 Serviceprovides 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 Requirements

The 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.

Emergency Locator Transmitters (2024)


What is emergency locator transmitters? ›

Emergency Locator Transmitters (ELTs) are self-contained units which provide signals to alert Search and Rescue (SAR) and the Air Force Rescue Coordination Center or Coast Guard Rescue Coordination Center during emergency situations.

How does an emergency locator transmitter work? ›

When activated manually - or automatically by immersion in water or as a result of high 'g' forces on impact - ELTs transmit a distress signal which can be detected by non-geostationary satellites and then located precisely by either or both of GPS trilateration and doppler triangulation.

Is a 121.5 ELT still legal? ›

§ 87.195 121.5 MHz ELTs. ELTs that operate only on frequency 121.5 MHz will no longer be certified. The manufacture, importation, and sale of ELTs that operate only on frequency 121.5 MHz is prohibited beginning July 10, 2019.

When must the battery in an emergency locator transmitter be replaced? ›

Batteries are required to be changed on that date or when the transmitter has been in use for more than 1 cumulative hour. The date stamped on the replacement battery must also serve as the new expiration date marked on the outside of the ELT.

What triggers an ELT? ›

An ELT is designed to emit an audible radio signal on various radio frequencies if it experiences a certain amount of G forces. Activating a switch, a low battery and other phenomena may also cause an ELT to transmit its siren type tone.

What are the four types of ELT? ›

There are five basic types of ELTs: automatic fixed (ELT-AF), automatic portable (ELT-AP), survival (ELT-S), automatic deployable (ELT-AD), and distress triggered (ELT-DT).

How long will ELT transmit? ›

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.

How accurate is the emergency locator transmitter? ›

Modern ELTs operates on 406 MHz. The signal of the ELT is detected by the COSPAS-SARSAT satellite network anywhere in the world. The network passes the alert to the nearest rescue authority. The COSPAS-SARSAT satellite network can detect the location of the ELT with an accuracy of 2 to 5 km.

What are the advantages of emergency locator transmitter? ›

Compared to PLBs that also use the 406 MHz band, the biggest advantage of the ELT is automatic activation. Further, aviation ELTs almost always have a more robust battery than handheld consumer products.

Is 121.5 always monitored? ›

The NOTAM states that, 'all aircraft operating in the United States national airspace, if capable, shall maintain a listening watch on VHF guard 121.5 or UHF 243.0. ' The value of 121.5 is that someone is always listening—every ATC facility monitors it.

What is the difference between 121.5 and 406 MHz? ›

In addition, activation of a 406 MHz ELT is detected by satellites, whereas, a 121.5 MHz signal relies on the aircraft being within the range of an air traffic service (ATS) facility or on another aircraft passing by at high altitude.”

How far can you fly without an ELT? ›

Unless something has changed, you can fly without an ELT if you have a single seat airplane or if you stay within 50 miles of where the aircraft is based. If you don't like those limitations, you're legal if you install a 121.5 ELT.

Can you fly with an expired ELT battery? ›

Batteries must be replaced after one hour of cumulative use or when 50 percent of their usable life has expired. Expiration date for replacing (or recharging) the battery must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record. Must be inspected every 12 calendar months.

What happens if I don't code my battery? ›

If you decide to replace a battery and don't register it – assuming it has IBS – you'll likely have issues of some sort. First, it's possible you'll experience either an overcharging or undercharging condition. If it's undercharging, sulfation can occur that degrades the plates inside the battery.

Will I need the radio code if I disconnect the battery? ›

When do you need to enter a code to use a car radio? Any time that your radio is disconnected from a battery or thinks it's been disconnected because of a flat battery, you might be asked to enter a code to use it again.

What is the purpose of the ELT? ›

Emergency Locator Transmitters (ELTs) are required for most general aviation airplanes (14 CFR 91.52). ELTs of various types have been developed as a means of locating downed aircraft. These electronic, battery-operated transmitters emit a distinctive downward sweep audio tone on 121.5 MHz and 243.0 MHz.

Can you fly without ELT? ›

a. No person may operate the aircraft unless the aircraft records contain an entry that includes the date of initial removal, the make, model, serial number and reason for removing the transmitter, and a placard located in view of the pilot to show “ELT not installed.” b.

What is the emergency frequency and what is it used for ivao? ›

After declaring an emergency or distress call with a squawk of 7700, a pilot can use the emergency frequency 121.500MHz in order to communicate his intention only if he cannot join any active air traffic controllers in this airspace after several attempts.

How does emergency location service work? ›

With ELS, the device automatically sends location information when a user contacts a configured emergency number. This happens via a location request made to the Android Fused Location Provider.

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