Veritable Aviation

A Look at Emergency Locator Transmitters

Emergency locator transmitters, or ELTs, are carried on nearly all general aviation aircraft in the United States. Should an accident occur, the ELT is designed to transmit a distress signal on the 121.5 and 243.0 MHz frequencies. New ELTs can also transmit signals on the 406 MHz frequency. Per a congressional mandate from 1973, ELTs are required to be affixed on nearly all civil aircraft registered in the United States, including general aviation aircraft.

When ELTs were first mandated, most general aviation aircraft were equipped with an ELT that transmitted on the 121.5 MHz frequency, the designated international distress frequency. The original ELTs were manufactured to the specifications of TSO-C91, an FAA Technical Standard Order. ELTs of this type have historically experienced an activation rate of lower than 25% in actual crashes, and a false alarm rate of 97%. A new TSO was developed in 1985 which greatly reduced or eliminated the problems of the earlier model. A newer model has since been developed that further improved the reliability. This new model, using digital technology, activates accurately up to 83% of the time and transmits a more accurate and instantaneous emergency signal. It operates on the 406 MHz frequency and allows search & rescue personnel to have vital information specific to you and your aircraft.

The ELT is mounted aft in the aircraft and is designed to be triggered upon impact. It can also be manually activated by a remote switch indicator and control panel indicator in the cockpit. Activation of the ELT triggers an audio alert as well as transmission of your Global Positioning System (GPS). A problem of ELTs is that they can sometimes issue false alerts. A false alert is an accidental or non-distress activation of an emergency beacon. Accidental activation can be caused by testing, mishandling, improper installation, or familiarity with the beacon’s operation. When a false alert occurs, search and rescue personnel are deployed immediately. This response is only stopped once they have confirmed that the activation was a false alert. Therefore, not only do false alerts spend valuable resources, they put the lives of rescuers at risk.

To prevent false alerts, there are three steps you can take. The first is to ensure that you are conducting regular self-tests and annual tests in accordance with the manufacturer’s instructions. The majority of false alerts occur during testing and maintenance, so the manufacturer’s instructions should be closely followed. The next step is to register your beacon with the NOAA (National Oceanic and Atmospheric Administration). Registration makes it easier for search and rescue operators to confirm that a false alert was indeed false and there is no danger they need to respond to. If you are registered, the relevant authorities can simply call you to confirm whether or not the alert was legitimate. Finally, if you realize you have accidentally activated your beacon, you can call the Air Force Rescue Coordination Center or the nearest FAA Air Traffic Facility to cancel the alert. The faster you do this, the more likely you are to prevent search and rescue personnel from being deployed.

 For all types of emergency locator transmitters and much more, look no further than Veritable Aviation. Owned and operated by ASAP Semiconductor, we can help you find all types of parts for the aerospace, civil aviation, defense, electronics, industrial, and IT hardware markets. Our account managers are always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, email us at or call us at 1-503-374-0340. Let us show you why we consider ourselves the future of purchasing.


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