There is no simple answer, but here are some questions to consider. Remember that all ADS-B Out transponders perform the same basic function no matter what frequency they use, and both 1090 and 978 options 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 solutions require you to maintain your existing Mode C transponder, so if you already have a solid 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 - their GDL 82 is a 978 solution that automatically syncs with your Mode C transponder.
  • Do you have a WAAS GPS? To meet the FAA requirements, an ADS-B Out package must include a WAAS GPS. If you already have a Garmin GNS 530W or GTN 750, you may be able to use that as a position source for ADS-B Out. If you do not have a WAAS GPS, make sure to purchase a solution that includes this.
  • 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 screens (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.

ADS-B Out comparison

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.


ADS-B Avionics

There are dozens of options for upgrading your panel with ADS-B. Here are the four most popular options.

Garmin GTX 335

1090 ADS-B Out with GPS

This is a great all-in-one solution for almost any airplane. The GTX 335 replaces your existing transponder, upgrading it to the latest digital features, and includes both a WAAS GPS and ADS-B Out.

Garmin GTX 335 - $2995


Garmin GDL 82

978 ADS-B Out with GPS

If you have a good Mode C transponder already, the GDL 82 is a low cost, easy-to-install option. It goes in between your transponder and your existing antenna, so the panel work is minimal. Includes WAAS GPS as well.

Garmin GDL 82 - $1795


Appareo Stratus ESG

1090 ADS-B Out with GPS

Upgrade your panel and meet the FAA mandate with this all-in-one solution. Includes 1090 ADS-B Out and a built-in WAAS GPS. Stratus ESG can also connect to your Stratus 2/2S/1S portable for ADS-B weather and traffic on your iPad.

Appareo Stratus ESG (certified) - $2995

Appareo Stratus ESG (experimental) - $2790


Appareo Stratus ES

1090 ADS-B Out without GPS

If you already have a WAAS GPS in your panel, Stratus ES is for you. It's a transponder replacement with ADS-B Out, but can connect to Garmin GNS/GTN and Avidyne IFD series navigators. Like Stratus ESG, it can also connect to a Stratus portable receiver.

Appareo Stratus ES (certified) - $2495

Appareo Stratus ES (experimental) - $2295


Cincinnati AvionicsCincinnati Avionics - Sporty's on-site avionics shop

Want to learn more about ADS-B or talk to an avionics pro about your airplane? Cincinnati Avionics, Sporty’s on-site avionics shop, are ADS-B experts. Whether it’s a basic transponder upgrade or an all-new glass panel, let us help you plan your next avionics upgrade.

Visit or call 513.735.9595