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Your Obsolete ELT May Reduce Your Chances Of Accident Survival

Did you know that by using your 121.5 MHz ELT, you could be risking up to 6 extra hours of search and rescue time, no satellite reception, and a low 15 nautical mile accuracy? Here's what you need to know about different kinds of ELTs and how they'll work to save your life.

John Chroston

How Your ELT Activates

According to NASA, "the vast majority of emergency locator transmitters (ELTs) are passive-sensing systems relying on internal battery power and utilizing a mechanical g-switch to activate the system when a crash event is detected. The performance characteristic of the crash sensor is established by RTCA-approved regulations (Radio Technical Commission for Aeronautics) and essentially requires the system to activate due to a change in velocity greater than 5 feet/second opposite the direction of flight, but not less than 2 times the force of gravity or 10 milliseconds of force application." Here's how NASA recently tested ELTs:

Alerting Search And Rescue

Cospas-Sarsat, the international satellite system for search and rescue, is an international coalition of over 40 nations. Their objective is "to reduce, as far as possible, delays in the provision of distress alerts to SAR services, and the time required to locate a person in distress at sea or on land and provide assistance to that person, all of which have a direct impact on the probability of survival." Participating nations provide satellite monitoring in addition to search and rescue services.

Paula Dobbyn - KTUU

In 2009, the Cospas-Sarsat system ended satellite based monitoring of 121.5/243-MHz frequencies after years of use. But why? According to NOAA, "They (121.5 MHz ELTs) have a 97% false alarm rate, activating properly in only 12% of crashes, and provide no identification data." Instead, Cospas-Sarsat satellites now monitor for 406 MHz ELTs. "These 406 MHz beacons dramatically reduce the false alert impact on SAR resources, have a higher accident survivability success rate, and decrease the time required to reach accident victims by an average of 6 hours."

It's still important during cruise flight that you always monitor 121.5 on the radio. Many ELTs designed to transmit over 406 MHz also transmit over 121.5. If you hear an ELT or distress signal, your help could be vital in search and rescue operations.

121.5 MHz vs 406 MHz ELTs

If you have a 121.5 MHz based ELT, satellites will no longer pick up your signal. It can only be picked up by ground stations within 1,800 nautical miles, ATC for instance, or planes monitoring 121.5 from overhead. Since 121.5 MHz beacons transmit anonymously, the only way to get information from the situation is to dispatch resources for investigation, which is both costly and time-inefficient. The real benefit? 121.5 MHz ELTs are relatively cheap as compared to their 406 MHz counterparts and still fulfill FAA requirements. You'll find them on many older general aviation aircraft.

The more costly 406 MHz ELTs offer some strong advantages. Beacon unique coding and registration to specific owners means that 70% of false alerts are resolved by phone and radio calls. Search and rescue groups are afforded first-alert response to 406 MHz ELTs, which means that they'll dispatch and locate a crash site anywhere from 3 to 6 hours sooner (depending on location) than for 121.5 ELTs. This is because 406 MHz success and accuracy levels are far greater than those on 121.5, for which authorities need to first verify that a 121.5 MHz alert was not false. Also, 406 MHz ELTs offer a 1 to 3 nautical mile accuracy, as compared to 12 to 15 nautical mile accuracy for those only utilizing 121.5 MHz. Many new aircraft come installed with these more capable ELTs.

For a full list of comparisons from NOAA, click here.

Regulatory Requirements For Your Airplane

Surprisingly, the Federal Aviation Administration doesn't require anything more accurate than a 121.5 Mhz ELT to be onboard your aircraft. According to NOAA, "the FAA has studied the issue of mandating carriage of 406 MHz ELTs. The study indicates that 134 extra lives and millions of dollars in SAR resources could be saved per year. The only problem is that 406 MHz ELTs are more costly to the consumer than their 121.5 MHz counterparts." In the past, AOPA lobbied against the implementation of a 406 MHz ELT mandate because of its expense. (Read here to find out about it.) But in the future, beacons with similar capabilities as those operating on 406 MHz may become mandatory, especially as their overall cost is reduced.


For a full listing of Federal Air Regulations about ELTs, check out 91.207. There are a few exceptions for when you don't have to carry an operable ELT onboard, like when your airplane is used for flight training solely within 50nm of its beginning airport.

ELTs have their own inspection criteria, including:

  • Every 12 calendar months after the last inspection for proper installation, battery corrosion, operation of the controls/crash sensor, and sufficient signal strength.
  • Battery replacement when the transmitter has been in use for more than 1 cumulative hour.
  • Battery replacement when 50 percent of their useful life (or, for rechargeable batteries, 50 percent of their useful life of charge) has expired.

Today, ELTs operating on 406MHz are much more affordable than when AOPA originally lobbied against their mandate. You can buy one today for roughly $500. No solution is perfect. In fact, there have been many cases where 406 MHz ELTs suffer failures or poor reception due to obstructions on the ground, technical faults, or user error. But for the most immediate and accurate search and rescue in the event you're in an accident, consider investing in a 406 MHz ELT if your airplane doesn't already have one. It's a small price to pay for something that could save hours of life-critical search time.

Jim Raeder

What do you think? Should 406 MHz ELTs be made mandatory on all aircraft? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at, and follow his flying adventures on his YouTube Channel.

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