Emergency Locator Transmitters

Choosing a beacon to save your bacon.

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The other day I arrived at the hangar and heard a very faint, high-pitched buzzer tone. Could it be tinnitus? Further inspection implicated the buzzer for the emergency locator transmitter (ELT). My first thought was to turn on a handheld radio to verify that I wasn’t transmitting a distress signal, and fortunately I was not. Disconnecting the wiring from the Ameri-King AK-451 caused the tone to stop. Initiating a test from the panel-mounted remote yielded no result at all, except that the main ELT batteries were probably dead, meaning that I had several hours of research and installation ahead, along with an expensive parts order. Upon removal, the main ELT batteries measured less than a quarter of a volt each, fair to call them dead.

ELTs are a subject that builders have a wide range of opinions about. Similar to deciding whether to prime internal aluminum parts or selecting a welding process, there is not a single consensus about the best way to proceed.

One school of thought doesn’t place much stock in the permanently installed ELT, instead favoring other search and rescue (SAR) aids like a personal locator beacon (PLB). These builders often say that in a serious mishap, the ELT is likely to be damaged, especially its antenna system. The antenna might be removed from the exterior or the coax feed line may be separated. These builders will often install an ELT that will meet the minimum requirement of FAR Part 91.207, diverting the financial savings to consumer-oriented devices like PLBs and satellite trackers. ELTs that only operate on the older 121.5 MHz VHF band are available cheap (as little as $100 on the used market), and some operate on D-cell alkaline batteries, lowering the cost of upkeep to the point of insignificance.

Kannad Integra (left) and Compact. Both ELTs transmit on 406 MHz and 121.5 MHz, but the Integra has a built-in GPS and an internal 406 MHz antenna.

The other school of thought favors the features of a more advanced permanently installed ELT. The better ELTs contain transmitters for the 406 MHz band, and the best include a GPS data source, allowing the unit to transmit its location to SAR services. 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. Also, there are no ongoing subscription fees for an ELT, as there are for devices like the SPOT personal tracker, which can cost as much as $200 per year.

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If those are the main advantages of a good ELT, the biggest disadvantages are in the initial purchase price, more complicated installation, and ongoing battery cost. Regulations require that these ELTs include a remote panel that mounts in the pilot’s view, so installing these units is more intensive, especially in an aircraft that is already completed.

The transmitting power for 406 units is usually 5 watts, compared to 0.1 watts for the old 121.5 MHz ELTs. These power-hungry transmitters leave no option for using household D-cell alkaline batteries, which drives the cost of battery replacement to the range of $100-$200, depending on the model, with replacement being required every 5-6 years. The initial cost of the unit is also a big factor, with the most advanced ELTs ranging from $500 at the low end, to a few options around $1,000-$1,200 and, as one would expect, prices climbing from there.

It’s possible that new batteries might have fixed my AK-451 ELT. But it might have had a different problem. Because Ameri-King is no longer able to support or repair their ELTs, I decided to replace this unit with a new ELT from a different manufacturer.

What’s Required?

Airplane operators have a few obligations when it comes to ELTs. FAR Part 91.207 requires ELTs in most cases, with a few exceptions. For example, aircraft equipped to carry not more than one person are exempt. There are also exceptions for temporary conditions, like ferrying a recently acquired airplane to a place where the ELT will be installed. The same section also requires a yearly inspection of the ELT for proper installation, battery corrosion, operation of the controls and crash sensor, and the presence of a sufficient signal radiated from its antenna. Of note to those who do their own maintenance, this inspection must be documented specifically in the maintenance records.

Somewhat embarrassingly, I purchased the Kannad 406 AF Compact without realizing that it did not have a GPS receiver. Fortunately, the mounting bracket, panel remote, and wiring are all a direct swap for the Integra.

Homebuilders enjoy relative freedom when it comes to equipment installations, but are we allowed to mix and match equipment in the ELT system, such as using an antenna or panel remote from a different manufacturer? It is surprisingly common to hear E/A-B owners say that their ELTs need not comply with TSO requirements, though 91.207 requires an “approved” ELT. There are long debates about this point, but the conservative choice is to install an ELT as instructed by the manufacturer, which includes all of the ancillary accessories, too. FAR 91.207 implies that our first duty is to our passengers so that they may be found if we don’t return them safely. We also have a duty to SAR resources, since often those folks are risking their own well-being to find us. When 91.207 requires the ELT to be “approved,” it is hopefully increasing the odds that our ELTs will be of sufficient quality to function reliably and reduce the burden of SAR to narrow down our location. Approval doesn’t necessarily make things function better, but this is a case where it seems the regulators are expecting us to not stray from the documented recipe.

ELTs were not always required, but like most regulations, a few high-profile crashes increased pressure to require the first 121.5 MHz ELTs, starting in the 1970s. Ross Nixon’s excellent book, Finding Carla: The Story that Forever Changed Aviation Search and Rescue, describes one such accident from 1967. At the risk of spoiling the story, sadly, it doesn’t end well for the surviving wife and daughter of the PIC.

From 121.5 to 406 MHz

In the early days of ELTs, overflying aircraft would report ELT signals. Eventually, satellites were developed to listen for distress transmissions and attempt to triangulate the source. In the early 1990s, the 406 MHz protocols were established, allowing a data link between the distressed transmitter and satellites. This data link was revolutionary because it could carry “who you are,” instead of the simple sweeping tone of the old ELTs. Nationwide use began in 2003, and since then, NOAA says that around one in nine of 406 MHz alerts are actual distress situations, compared to less than one in 500 for 121.5 MHz. This high rate of false alarms, combined with the increased adoption of 406 MHz units, led SAR agencies to discontinue monitoring 121.5 MHz signals by satellite, starting in February 2009.

The encoded message from 406 MHz units allows SAR organizations to start the search by calling the registered owner of the distress beacon. According to NOAA, this eliminates 70% of false alarms quickly. Their website lists the number of rescues per year, with 200-300 per year being typical in all uses, including those other than aviation. In 2016 there were 23 people rescued in aviation uses.

Systems can always fail, and sometimes ELTs or PLBs don’t operate as expected. One study found 121.5 ELTs to activate in only 12% of crashes. Even considering those odds, I think there is a good case for maximizing the available SAR tools when selecting emergency equipment. This places me in the camp of choosing a robust ELT for the airplane, even with the understanding that it might not work in a crash. I also carry a PLB and take SAR measures like letting a responsible party on the ground know where and when I’ll be flying. I also use amateur radio APRS beaconing on occasion, and use a Mode-S transponder that leaves a trail with “the government,” for better or worse.

Completed Kannad ELT installation in the tail cone of my Bearhawk.

This leads back to my failed ELT. Internet research points to a failure mode where the small battery in the remote dies prematurely. This can begin a process that drains the main ELT battery on the buzzer, which seems to have happened in my case. One option would be to replace the main and remote batteries at a cost of around $60-$100 and hope that would fix things. There was also a possibility that my unit had another problem, but since Ameri-King was recently subject to an airworthiness directive (AD) and a cease and desist order from the FAA, they are no longer able to support or repair the ELT. The AD does make provisions to repair the ELT, but since Ameri-King is unable to execute the repair, I’m not sure who is. Even in the best case of replacing the batteries and carrying on, having a failure mode like this was definitely sub-optimal. How long would it be before the same thing happened again?

Looking at the big supply houses like Aircraft Spruce and Wicks, there are a few different ELTs to choose from. Somewhat arbitrarily, my own search only considered 406 MHz-capable units, and I stopped looking when the price exceeded much more than $1,000. This led to the ACK E-04, ARTEX 345, Emerging Lifesaving Technologies 406, Kannad 406 AF Compact, Kannad Integra, and Pointer 8000. The Emergency Beacon Corp (EBC) units are in that price range without the panel-mounted remote, but adding the remote pushes the price over $1,200, similarly with the ARTEX ME406. Some of the factors in my shopping were the cost of battery replacement, ease of installation with my existing wiring (six conductors from the panel to the ELT), and GPS integration.

GPS Integration

There are two different strategies for GPS integration: serial GPS data relayed to the ELT from the airplane’s existing navigation system, and internal GPS capability within the ELT. The advantage of using serial GPS data is that the source is probably a good one, with its own external antenna. If it isn’t a good source, this will become evident as you try to navigate the aircraft. One disadvantage is the requirement to run two more wires back to the ELT for the serial data. Another is the possible failure point of that wiring, including the software settings of the serial output on the GPS. If the hardware or software of this link is broken, it may be not obvious in a test of the ELT, depending on the unit. An ELT with its own internal GPS doesn’t have the vulnerability of a link to the panel, but in airframes that block signals (aluminum and carbon fiber especially) it will require its own external antenna. The units with internal GPS receivers also cost more.

GPS input to the ELT allows the ELT to include the “where you are” along with the “who you are” in its encoded distress message. There are 406 MHz units that do not have GPS capability, but this is not ideal, and here’s why: There are three different types of satellites that receive the distress signal, and all require line of sight to the beacon. If the distress signal does not include location, it takes two low earth orbit (LEO) satellites hearing (thus, “seeing”) the transmission in order to determine the location. These satellites move relative to the ground, which allows them to use Doppler location processing to determine the location of the beacon. This may take an hour or more, and certain terrain features may preclude contact with the satellite at all. There are geostationary satellites that also listen for distress signals. The geostationary satellites orbit higher and are more likely to see you in the bottom of a canyon. And because they are stationary, they are able to receive the signal immediately and pass along the identity of the beacon, allowing SAR resources to start the telephone calls. But since they are not moving relative to the ELT, the geostationary satellites are not able to triangulate position. If the ELT is GPS-enabled and transmits its location, then the geostationary satellite will not need to wait for the LEO satellites to triangulate, and SAR resources will know the beacon’s position nearly immediately. Also, an onboard GPS solution is more accurate than the Doppler-derived position, comparing 1-3 nautical miles to less than 100 yards. Recently, the satellites powering the GPS system have started launching with equipment to also detect 406 MHz distress signals. As the constellation is gradually replaced, these systems will further enhance and expedite location sensing by Doppler techniques.

One nice feature of the ARTEX 345 is that it doesn’t require a battery for the buzzer or the panel remote. Although it doesn’t have an internal GPS, the ARTEX 345 can accept serial GPS data.

Decision Time

Getting back to the catalogs, it was time to decide on a new ELT. For my installation, I eliminated the Emerging Lifesaving Technologies unit because it does not transmit on 121.5 MHz. Satellites no longer monitor 121.5 MHz, but lots of other folks still do. Most SAR crews can still use it for homing to narrow down the location of the ELT, and from a purely functional standpoint, my panel-mounted and handheld VHF radios allow me to tune 121.5 to verify that I am not transmitting a distress signal. I’m not equipped to do this with the UHF 243 or 406 MHz bands.

The ACK E-04 was a very tempting choice, in part because it costs much less than the Kannad. According to the installation manual, the ACK requires a battery in the panel remote and a battery in the remote buzzer. These batteries are not the same as each other, nor are they a common size that I’m likely to find in a non-specialized store. The ACK uses an external GPS source with a serial connection, which can be an advantage or disadvantage, depending on the preference of the installer. On the plus side, the panel remote is a direct swap for the Ameri-King remote, and replacing the primary battery is a little bit less expensive than the Kannad or ARTEX.

The ARTEX 345 is priced similarly to the ACK, and on the plus side, it does not require a battery for the buzzer or the panel remote. It weighs a little less than the others, and it does not have its own internal GPS, but can accept serial GPS data like the ACK. I ruled out the Pointer 8000 because it did not include a GPS sensor, though it was priced like the ones that did.

In the end, I chose the Kannad Integra. It costs a little more than the ACK and ARTEX, but I appreciated that it had its own internal GPS, and that it only required three conductors between the main unit and the panel remote. Kannad provides a kit specific to Ameri-King replacement, including a panel remote that fits the same footprint as the Ameri-King (part number RC102), but the pricing is much more favorable on pre-packaged kits that include the ELT and Kannad’s RC200 remote. It would have been nice if the RC200 remote was large enough to cover the footprint of the old Ameri-King remote, but this is remedied with a little filling work in the panel. Kannad also offers the Compact model, which has the same external dimensions as the Integra, but does not have a GPS sensor or an internal 406 MHz antenna. The Integra can operate with a separate external antenna, but its internal antenna provides a nice backup in case the external antenna is compromised. The Kannad warranty is 10 years, compared to 2 years for most others. Also, the Kannad does not require a separate buzzer, reducing the parts count.

I completed the ELT swap with a few mornings in the hangar and registered the ELT with NOAA. As they frequently point out, many of the benefits of a 406 MHz beacon are lost if the owner does not register it. It is equally important to deregister any 406 beacons that you transfer or get rid of. If the registration website is not working, a toll-free telephone number is staffed to help with the process. The experience of researching and replacing the ELT has given me a much better understanding of the SAR system and the need for periodic tests of the unit. It’s not pleasant to remind ourselves that all flights do not end well, but we owe it to our passengers and families to ensure our equipment is up to its job in such rare situations.

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