You probably know by now that most airplanes will have to be equipped with ADS-B Out by 2020 in order to meet the FAA mandate. Beyond that basic issue, though, there are still a lot of questions to consider. One of the first is 1090 vs. 978. That is, should you install an ADS-B Out transponder that works on the 1090 MHz frequency (sometimes called 1090ES) or the 978 MHz frequency (sometimes called a 978 UAT)?

There is no simple answer, and all ADS-B Out transponders perform the same basic function no matter what frequency they use. Both meet the 2020 requirement. But there are some important differences to consider, depending on the type of airplane you fly.

  • What is the total installed cost? The cost of ADS-B Out hardware is only one part of the equation – be sure to ask about the installation time and cost as well. 1090ES transponders are mounted in the avionics stack, in place of an existing Mode C transponder, so they don’t require the removal of the interior like most 978 installations (which are typically mounted in the tail of the airplane). In many cases, the installation cost is 30-50% less for a 1090 solution.
  • How old is your Mode C transponder? In addition to ADS-B Out, you’ll still need to have a traditional transponder after 2020. If your existing Mode C transponder is on its last legs, a 1090ES transponder is probably the right answer, since it checks both boxes. In addition to meeting the mandate, you’ll get the features of a new transponder, like a clear digital display, push-button code entry and a dedicated VFR button. 978 requires you to maintain your existing Mode C transponder, so if you already have a new one you may be able to save money with a UAT.
  • How integrated is each solution? Some 978 UAT transponders require separate control heads to synchronize the squawk code with your existing Mode C transponder – or even a separate panel-mounted indicator light. 1090ES solutions are integrated solutions: simply connect it to your existing transponder antenna and altitude encoder, then add a WAAS GPS antenna if a built-in GPS is included. The one exception is Garmin’s GDL88/84, 978 solutions that automatically sync with your Mode C transponder.
  • Do you fly internationally? 978 UAT transponders are limited to use in the United States, so pilots traveling to Canada, Mexico or the Caribbean should choose a 1090ES transponder.
  • Do you fly above 18,000 ft.? Aircraft equipped with 1090ES transponders are authorized to fly at all altitudes, whereas 978 UAT transponders are not permitted above 18,000 ft.
  • What multi-function display do you have? If you have a glass cockpit or a modern navigator, a 978 UAT can display subscription-free weather and traffic on those beautiful color screen (if your 978 solution is an ADS-B In model in addition to Out). If you already receive weather and traffic with a portable ADS-B receiver, you can probably save some money by just choosing Out.


Mac McClellan, writing in EAA Sport Aviation, sums it up well: “If you plan to keep your airplane much beyond 2020, I think the new transponder route makes a great deal more sense… the 1090ES transponder install requires half the new antennas, no new cockpit panel unit, and a fraction of the wires.” On the other hand, if you have a glass panel, a remote-mounted 978 unit may make a lot more sense – especially if it’s done as part of a larger avionics upgrade.

Whichever ADS-B Out solution you choose, be sure to focus on the total installed cost of your new avionics. Read the fine print and ask informed questions about labor costs to install your new transponder and any additional parts that may be required. The right answer for you is the package that meets the 2020 ADS-B mandate, offers the upgrades your airplane needs, and is affordable to install.

gdl 84 twoAffordable, Stand-alone ADS-B “Out/In” Solution

  • Dual-link solution meets U.S. ADS-B “Out” requirements
  • Displays subscription-free ADS-B weather and datalink traffic on your iPad® or other compatible products
  • Packaged with Flight Stream™ 110 or 210 device for wireless connectivity with tablets/mobile devices via Garmin Connext™
  • Built-in SBAS/WAAS GPS receiver
  • Supports patent-pending TargetTrend traffic and SURF display

For U.S. aircraft owners seeking an easy, cost-efficient way to meet the requirements for ADS-B “Out” equipage – while enjoying the “In” benefits of subscription-free weather and traffic – the Garmin GDL 84 offers the ideal solution.

This is Do-it-all ADS-B

Under the provisions for NextGen ATC implementation, all aircraft operating in controlled U.S. airspace will need to be equipped with Automatic Dependent Surveillance – Broadcast (ADS-B) “Out” technology before end-of-year 2019. The GDL 84 offers a smart, all-inclusive installed solution for the many GA pilots who operate below Class A airspace (18,000 feet) in the U.S.

Dual-link Means Complete Air-to-air Coverage

Using its built-in WAAS GPS receiver, the GDL 84 generates precise information about your aircraft’s position, track and ground speed. It then broadcasts this information to the ADS-B ground station network for relay to ATC and other ADS-B “In” equipped aircraft in the airspace. The dual-link (1090 MHz and 978 MHz) frequency reception capability of the GDL 84 enables it to receive air-to-air position reports directly from other aircraft, so you can always see those ADS-B broadcasting aircraft in your vicinity, regardless of which datalink frequency they’re using. Accessing both of the available ADS-B frequencies used in the U.S. system, your GDL 84 ensures a more complete situational picture – for added confidence in all phases of flight.

Stream Weather and Traffic to Your iPad

The GDL 84 package doesn’t depend on an installed display to provide the benefits of ADS-B “In” to your cockpit. With its included Flight Stream wireless gateway device, the GDL 84 works to keep your NextGen compliance costs low, while providing the means to uplink and display subscription-free U.S. ADS-B weather and traffic on your Garmin Pilot™ equipped iPad or other compatible mobile device. On the weather side, you can view animated NEXRAD imagery, METARs, TAFs, winds and temperatures aloft, PIREPs, NOTAMs and more. Plus, on the traffic side, your tablet can display moving target symbols and alerts to help you recognize any potential conflict scenarios in busy airspace.

Access More Advanced Capabilities

In addition to audible target alerts (“Traffic. Two o’clock. High. Two miles.”) the GDL 84 will also support the latest in ADS-B traffic display capabilities, which can be viewed with the Garmin Pilot app on your iPad or other compatible tablet. Our patent-pending TargetTrend relative motion tracking technology, for example, offers a faster, more intuitive way of judging aircraft trajectories and closure rates in relation to your aircraft’s flight path. Likewise, in the airport environment, Garmin SURF technology works with SafeTaxi® to support geo-referenced display of ADS-B-equipped targets, including taxiing aircraft and ground service vehicles, on the surface diagram.

Single-entry Squawk Code

The NextGen equipage rules require your ADS-B “Out” source must be able to squawk the same code as your transponder. The GDL 84 has the ability to automatically synchronize with your onboard transponder for its squawk code, and then transmit that data through its own datalink. Not only does this provide a single point of data entry for ADS-B “Out”, but it also allows you to meet the new regulations without the need for expensive control system or transponder upgrades. Thus, GDL 84 works in the background to make code entry fast and easy – while helping to make your path to ADS-B compliance as simple, straightforward and cost-effective as possible.

You Can Grow From Here

As the NextGen airspace system evolves, you may find that you want to add ADS-B weather and traffic interface capabilities to an MFD or other navigation display onboard your aircraft. While the GDL 84 is designed for use with compatible tablets and smart devices only, Garmin does offer an easy growth path to installed-system display capability. For a minimal cost, your GDL 84 can be returned to Garmin for factory upgrade to a GDL 88 configuration. With this upgrade, your receiver can bring all the graphical benefits of ADS-B to your in-panel Garmin flight displays.

You have questions. We have answers.

ads-b airspace requirementsBy now, you’ve probably heard of Automatic Dependent Surveillance-Broadcast (ADS-B) and the requirement for many airplanes to add an ADS-B Out transponder to the panel. But you may be confused about what exactly ADS-B is, why you should care and what you should do.

That’s where we come in. Count on Cincinnati Avionics to guide you through the process from start to finish. We’ll explain what ADS-B is all about and what it offers for pilots, so you can make a confident decision about your airplane’s avionics. We also offer a full complement of ADS-B avionics to suit almost any aircraft, from names you trust: Garmin, Appareo, Bendix/King and more.

Read our helpful resources below, and feel free to contact us anytime to talk one-on-one: call 513.735.9595 or email

Understanding ADS-B

At heart, ADS-B is a new way for Air Traffic Control to separate airplanes, but it can also offer free datalink weather and traffic. Here are 5 things to know before you upgrade to ADS-B:

  1. ADS-B Out avionics will be required by January 1, 2020 in most airspace where you need a Mode C transponder today.
  2. An approved WAAS GPS must be included in your ADS-B Out solution.
  3. ADS-B Out compliance must be with panel-installed equipment (no portables).
  4. ADS-B In equipage (for weather and traffic) is completely optional.
  5. Avionics are available from Garmin, Bendix/King, Appareo, Aspen and others, starting under $5,000.

Want to learn more about ADS-B?

Avionics Options

In just the past 18 months, a number of exciting ADS-B products have been announced. There has never been a better time to consider upgrading your panel. Below, find some of the more popular options. Request a quote or contact us for complete pricing and information.


GDL 82 – an all-in-one solution, including WAAS GPS, that retains your existing Mode C transponder. More info


GTX 335/345 – a 1090ES transponder (ADS-B Out), with internal GPS. 345 adds ADS-B In and a Bluetooth connection for tablets. More info

Already have a GTX 330 Mode S Transponder? In most cases, this can be upgraded to ES. Contact us for details.


Appareo Systems


Stratus ESG – a 1090ES transponder with certified WAAS GPS, an “all-in-one-box” product for compliance. The Stratus portable ADS-B In receiver can be connected to Appareo’s Out transponder for an amplified ADS-B In experience on ForeFlight. Also available without GPS (Stratus ES). More info


L3 Aviation

Lynx Traffic & NEXRAD


Lynx MultiLink Surveillance Systems is a simple transponder replacement packed full of ADS-B benefits. More info


Bendix/King by Honeywell

Bendix/King KT 74

KT 74 – a 1090ES (ADS-B Out) transponder that is a “plug and play” replacement for the KT 76A/C. More info

Many panel-mount ADS-B transponders, in addition to portable ADS-B receivers like the Garmin GDL 50 and the Appareo Stratus, can receive ADS-B traffic in addition to weather. But unlike weather, which is broadcast continuously, traffic is only transmitted in response to specific prompts. This can make ADS-B traffic very confusing–when does it work and when doesn’t it work?

To help, we’ve created this series of graphics, which shows three common scenarios:


Graphic 1: The most likely scenario, where you are flying with a portable ADS-B receiver, but do not have an ADS-B Out transponder installed in your panel. Here, you’ll receive any airplane that is transmitting ADS-B Out via air-to-air (no ground station required). Most airplanes do not have ADS-B Out, so this is fairly limited. You will not see regular, Mode C targets.



Graphic 2: In this case, you are still flying with a portable ADS-B receiver and no ADS-B Out in your airplane, but you are close to another aircraft that is ADS-B Out equipped. In this case, that ADS-B Out airplane is waking up the ground station and is receiving a custom traffic picture for a 30 mile “hockey puck” around that airplane. If you are close enough to that airplane, your portable receiver can listen in on that traffic message. While you won’t get a complete traffic picture, you will get a better one, since the ground station transmits Mode C targets in addition to ADS-B targets.



Graphic 3: This is the best possible case. You have an ADS-B Out transponder in your airplane, so you are transmitting out to the ground stations and creating your own “hockey puck” of traffic information. You’ll see all traffic within a 30 mile diameter and 3500 ft.

For more information on ADS-B and how to upgrade your airplane, visit our ADS-B page.

In an industry famous for its ridiculous acronyms, ADS-B stands out for being uniquely confusing. Lots of pilots use the term, but few really know what it means. And who can blame them–it’s incredibly complicated. Unlike WAAS or LORAN, you can’t even pronounce it!

So what is ADS-B? Why should you care about it? Can you just ignore it?

No. While ADS-B may be confusing, it’s probably the most important technological change you will have to deal with as a pilot over the next two decades. So it’s worth the effort to learn this new language.

ADS-B system diagram
ADS-B involves ground stations, GPS satellites and panel-installed avionics.

What is it?

At heart, ADS-B is really just a new way to manage air traffic. As such, it will eventually replace radar as Air Traffic Control’s (ATC) primary tool for separating aircraft. It’s different from radar in that it does not depend on controllers in a central location watching radar scopes. Instead, aircraft self-report their GPS position in a networked environment, so pilots can see the entire air traffic picture around them. There is also the added benefit of datalink weather and traffic available through ADS-B.

ADS-B stands for Automatic Dependent Surveillance-Broadcast. It’s a dreadful name that only an engineer could love, but it happens to be fairly descriptive. Let’s look at each part of it:

  • Automatic–properly-equipped aircraft automatically report their position, without need for a radar interrogation
  • Dependent–ADS-B depends on aircraft having an approved WAAS GPS on board and an ADS-B Out transmitter
  • Surveillance–it is a surveillance technology that allows ATC to watch airplanes move around
  • Broadcast–aircraft broadcast their position information to airplanes and ATC

This system doesn’t need radar to work properly, but it will depend on a network of ground stations to receive aircraft reports and send them back to ATC. These stations also transmit weather and traffic information back up to properly-equipped aircraft. This network currently consists of over 500 stations, and the initial phase is complete. So when you hear that ADS-B moves from a “ground-based” radar system to a “satellite-based” system, it’s only partially true.

By the way, you’ll often hear the phrase NextGen used interchangeably with ADS-B. Technically, NextGen (or the Next Generation Air Transportation System) is the FAA’s omnibus plan for modernizing air traffic control. ADS-B is a critical part of NextGen, but it’s only one part of it.

Now that we know what ADS-B is, how does it work?

Out vs. In

ADS-B is made up of two main parts: ADS-B Out and ADS-B In. Out is of interest to controllers, while In is mostly of interest to pilots.

ADS-B coverage map
ADS-B coverage is excellent above 5000 ft. AGL.

ADS-B Out is a surveillance technology for tracking aircraft–it’s what ATC needs to manage traffic. It reports your aircraft’s position, velocity and altitude once per second. This transmission is received by ATC and nearby aircraft and this data makes up the equivalent of a radar display. Most aircraft will be required to have ADS-B Out by 2020 (see below).

ADS-B In allows an aircraft to receive transmissions from ADS-B ground stations and other aircraft. This is how pilots can get subscription-free weather and traffic in the cockpit. Adding ADS-B In is strictly optional. While it offers some great benefits, the FAA is only concerned about you equipping with ADS-B Out–the free weather and traffic is simply the carrot to get you to write a check.

Note that there are various combinations of these two: Out-only equipment that simply meets the FAA requirement, In-only portable devices that receive weather, and ADS-B In/Out products that do it all. One thing to keep in mind–there is no such thing as a portable ADS-B Out device. All Out equipment must be panel-installed.

1090 vs. 978

You would think that would be the end of the confusion with ADS-B, but unfortunately you would be wrong. Due to concerns about frequency congestion (and other issues too boring to detail here), there are two different datalink technologies that meet the ADS-B requirement: 1090 MHz ES and 978 MHz UAT. As the names imply, these are simply different frequencies used by the equipment to transmit and receive data.

Garmin GTX 335
1090ES transponders like Garmin’s GTX 335 are all-in-one ADS-B Out solutions.

1090 Extended Squitter (ES) is based on 1090 MHz, just like our Mode A/C/S transponders. In fact, some Mode S transponders (like Garmin’s GTX 330) can be upgraded to an ES transponder by upgrading the software and adding a WAAS GPS. This is the only technology accepted outside the US and above 18,000 feet, so it will be popular with turbine airplanes. ES receivers can detect other aircraft with ES transmitters air-to-air, and they can receive other traffic information uplinked from ADS-B ground stations. But there is no weather datalink on 1090.

978 products are sometimes called UAT, for Universal Access Transceiver. This is only available in the US, and only below 18,000 feet, so it is aimed mostly at piston aircraft. Like a 1090 ES receiver, UATs can detect other airplanes with transmitters on the same frequency (978 MHz) air-to-air and also receive the rest of the traffic picture from ADS-B ground stations. But weather is also transmitted over 978 MHz, an added bonus.

This ends up being a real mess. You can have all kinds of different equipment: 978 Out only, 978 Out/In, 1090ES Out only and even a combined 1090ES Out/978 In. At the end of the day, you should choose the Out frequency that matches your flying. If you fly above 18,000 feet or outside the US, 1090ES is your only option. If you don’t, a 978 UAT could work. After you’ve chosen your Out frequency, the only other decision is whether you want ADS-B weather; since that’s only available on 978, that’s a simpler decision (but remember that your 978 receiver could be a portable).

Weather and Traffic

Since weather and traffic come into play so much during any discussion of ADS-B, let’s define some terms: FIS-B and TIS-B. These are the two products that we can receive via ADS-B In.

Stratus 2S
Portable ADS-B receivers like the Stratus are great for use with an iPad, but they do not meet the ADS-B Out mandate.

Flight Information Services-Broadcast (FIS-B) is just a fancy name for datalink weather. Only available with a 978 MHz receiver, the end product is very similar to what we’re used to seeing with XM Weather. NEXRAD radar, METARs, TAFs, TFRs, AIRMETs and other information is continuously updated in flight, and all this can be displayed on either a panel-mount MFD or a portable device like an iPad. There is no monthly subscription fee with FIS-B (your tax dollars paid for it), which is a nice feature. But unlike XM Weather, ADS-B weather uses the network of ground stations, not satellites. That means coverage, while pretty good now and getting a lot better, is not as universal as XM.

Traffic Information Services-Broadcast (TIS-B) is what the name suggests–datalink traffic. But leave it to the FAA to make this complicated. Unlike ADS-B weather, which is broadcast to anyone in range of the ground stations, ADS-B traffic is a custom report that is only sent to aircraft with ADS-B Out. If you’re flying with an ADS-B Out transmitter in your airplane, you’ll get an excellent picture of all traffic within roughly 30 miles of you. But if you’re not flying with an ADS-B Out transmitter (say, with a portable ADS-B In receiver), TIS-B is fairly unreliable. Read this article for complete details on this confusing subject.

Changes for ATC

Remember that, while datalink weather and traffic are nice, the whole point of ADS-B is for ATC. And the FAA has some grand plans for how ADS-B will transform the way it does business, claiming it will reduce aviation’s environmental impact, improve safety and increase capacity at airports. A lot of this seems awfully optimistic, and will not be a reality for many years (if ever).

But there are some more realistic improvements that will probably come to pass sooner. Since ADS-B is so much more accurate than radar, separation minimums can be reduced. This should lead to at least a little more direct routing and some increased capacity. Because ADS-B does not require radar, air traffic control will be available in many remote areas that cannot be served by radar. ADS-B will also impact ground operations, giving controllers the ability to prevent runway incursions and ground traffic conflicts.

But of course this won’t come free.


Final ADS-B Out rules were finalized in 2011. Those rules say that by 2020, all aircraft will be required to have ADS-B Out equipment to fly in Class A, B and C airspace, plus Class E airspace above 10,000 feet but not below 2,500 feet. You’ll also need it within the 30nm “Mode C Veil” around Class B airports. So in general you’ll need ADS-B Out most of the places you need a Mode C transponder today–and you’ll need to keep that Mode C transponder if you install 978, because radar will be the backup for ADS-B.

ADS-B airspace
ADS-B Out will be required by 2020 for flight in most controlled airspace.

That does mean some pilots will not have to upgrade to ADS-B Out. If you fly a Cub on sunny Saturdays away from major airports, you’ll be exempt. But if you use your airplane for any type of transportation flying, plan on equipping with ADS-B Out by 2020.

This ADS-B Out transmitter must be a panel-installed, certified solution (again, no portable ADS-B Out option). An approved WAAS GPS source is also required, to make sure your reported position is accurate. Remember, though, there is no mandate for ADS-B In equipment.

There are a number of products available now to satisfy this requirement, from major avionics manufacturers like Garmin, Appareo and others. Prices vary significantly, but average about $5000 (including installation).

What should I do?

This may all sound overwhelming, and the FAA certainly has made things complicated. But the end result is pretty simple: by 2020, you will most likely need to install an ADS-B Out transmitter in your panel (or upgrade your Mode S transponder if you have one). The only questions are what solution to install and when to do it.

The market for ADS-B products is pretty mature now, with features going up and prices coming down. Garmin’s GTX 335/345 announcement in early 2016 showed that the avionics giant is serious about owning the ADS-B market, but there are a number of other companies shipping ADS-B boxes of their own. Some of these are Out-only, in an attempt to check the box for 2020 compliance as cheaply as possible. Others are full-featured Out/In products that can connect to a variety of MFDs. (see all the options here)

Of course there is already a red hot market in portable ADS-B receivers, like the Stratus, Garmin GDL 50 and Dual XGPS 190. These are easy and inexpensive ways to get subscription-free weather on your iPad or portable GPS, and have become quite popular over the past year. But they do not address the 2020 mandate for ADS-B Out, and traffic is unreliable.

One option that could become more appealing is to combine these two products: install an ADS-B Out transponder in the panel, but use a portable receiver for ADS-B In. That would comply with the 2020 rule at a fairly low cost, but give you complete weather and traffic datalink. The only major drawback here is that your weather and traffic would not be displayed on the panel, but rather on an iPad or other portable device. And remember that you’ll need an approved GPS source for your ADS-B Out box–either a WAAS GPS or a GPS receiver built-in to your transponder.

When to purchase an ADS-B Out solution is a tougher decision. If your transponder quits, it’s probably sensible to replace it with a full ADS-B Out unit instead of spending the money on a soon-to-be-outdated Mode C transponder. If you want free in-flight weather and a reliable traffic picture, an ADS-B Out transponder is a good investment. While you certainly shouldn’t feel like you have to upgrade to ADS-B Out today, it’s probably not wise to wait until the last minute.

No matter what decision you make, it seems clear that ADS-B is coming to US airspace. In time, it might even be a good thing.

Want to learn more? Contact Cincinnati Avionics: 513.735.9595 or