For some owners, an ADS-B upgrade could seriously blow the budget since it might also include buying a new transponder system. That’s because the requirements in FAR 91.215 still apply, even when the ADS-B mandate takes effect in 2020.
The good news is our recent market sweep uncovered a number of next-generation multifunction transponders that handle all ADS-B and transponder functions in one box, even serving as nifty weather and traffic displays. Better yet, a one-box solution eases concerns about long term cross-brand compatibility. Still, the buying decision is muddied by rapidly changing ADS-B solutions.
In this article, we’ll put a fresh eye on new models and interfaces, plus offer tips on evaluating an existing vintage model.
BASIC MODE A/C
With the ADS-B mandate roughly four years away, it’s time to evaluate the health, age and supportability of your existing transponder system. It should be addessed as a system because the supporting antenna, cabling and altitude encoder is just as important as the transponder.
As we describe in the sidebar on page 7, if you’ve neglected the required FAR 91.413 transponder inspection and certification (you do know it’s required every 24 calendar months, whether you fly IFR or VFR, don’t you?), now is the time get the aircraft to a shop for an evaluation.
If you haven’t replaced a transponder in a while, you might be surprised at the advances in even basic models. Few manufacturers still offer plain-vanilla Mode A/C transponders. Instead, the trend has shifted to Mode S technology with 1090ES (extended squitter) ADS-B output. And even the few models that don’t have ADS-B output sport advanced features, potentially reducing installation costs and increasing long-term reliability.
For instance, the Sandia Aerospace STX165 is not only designed for tight panels (it can drop into a standard 3-ATI instrument cutout), it also has an integral Mode C altitude encoder, which is certified to 35,000 feet. The encoder can feed pressure altitude data to other onboard systems over the STX165’s serial databus.
When installing an ADS-B system (which will likely require pressure altitude input), shops need to evaluate the health of the altitude encoder, as an aging model might not be up to the task. The STX165 solves the dilemma, while also simplifying the interface. It references pressure altitude by connecting directly to the aircraft’s static system.
This means the aging static lines that snake through the airframe to the old encoder can be removed. These lines are often a source of leakage, so reducing the number of lines and fittings is a good thing.
You can even advance the interface with Sandia’s $350 STP78 temperature probe. The sensor provides an input to the transponder for displaying density altitude, icing alerts and temperature readout.
The STX165 has a simple feature set that consists of dual rotary function knobs, a dedicated VFR squawk button, ident button, plus it has a sunlight-readable and backlit LED display. At $1850, we think the STX165 is a good value for an entry-level upgrade.
BendixKing still makes the KT76C (built to order), a digital model that made its debut when Cessna revived its single-engine airplane line in the late 1990s. The KT76C—which uses surface-mount circuit board technology—(it still uses a cavity tube, despite having a digital front end) is an easy replacement for the mechanical KT76A. It can use the existing wiring and the same mounting rack.
On a side note, the cavity tube in analog transponders is the high-cost component associated with the set’s power output. It generates heat, huge amounts of voltage and will inevitably fail. It pays to use caution when buying a used transponder. We suggest first sending it through a careful bench evaluation—paying close attention to the health of the cavity—by a shop you trust.
Garmin dropped its entry-level analog GTX320A transponder, but still offers the digital GTX327. We like that it has a short chassis, making it versatile in panels that have limited clearance behind the radio stack, or when mounting it outside of the center stack.
The GTX327’s reliability has been good, although we’re hearing of function key failures on units that have been in service for a long time. Flat-rate factory repair is around $600.
The GTX32 is the remote version of the GTX327. It can be channeled from the GTN750 touchscreen navigator, eliminating the need to mount the transponder in the radio stack.
With an RS232 serial data interface, the GTX327/32 interfaces with the GNS and GTN navigators, automatically going into airborne and ground mode, while automatically starting and stopping a flight timer on the takeoff and landing rollout.
But what we really like about the GTX327/32 is its enhanced compatibility with Garmin’s GDL88 and GDL84. These UAT ADS-B transceivers don’t require remote control panels because they interrogate the transponder and communicate with it through the serial databus, automatically keeping both the ADS-B and Mode A transponder codes in sync. Some other serial bus-equipped models will work with the GDL88 and GDL84, but you’ll need to check with your installer to ensure full compatibility.
Want ads-b with that?
If you do, the market is flooded with 1090ES ADS-B Out transponders. Check out the ADS-B buyer’s guide in the June 2015 issue of Aviation Consumer. The choices are overwhelming, although a choice may be easier when you consider which equipment will be interfaced with the transponder. Think long-term, in terms of software and brand compatibility.
The first step is to decide what you will use for an approved ADS-B WAAS position source. WAAS position is an important piece of ADS-B data required for a 1090ES transponder’s data output. That is, if the transponder doesn’t have its own GPS receiver. More on that evolving trend in a minute.
The software and databus configuration in Garmin’s GTX330ES (and remote GTX33) 1090ES ADS-B transponder is based on an architecture that includes its own GNS530W/430W and GTN-series WAAS navigators, although there is compatibility with Avidyne’s IFD540 and IFD440 GPS. These navigators are designed to drop into a GNS530W/430W installation, so it’s logical they can work with a GTX330ES.
For some owners, an ADS-B upgrade could seriously blow the budget since it might also include buying a new transponder system. That’s because the requirements in FAR 91.215 still apply, even when the ADS-B mandate takes effect in 2020.
The good news is our recent market sweep uncovered a number of next-generation multifunction transponders that handle all ADS-B and transponder functions in one box, even serving as nifty weather and traffic displays. Better yet, a one-box solution eases concerns about long term cross-brand compatibility. Still, the buying decision is muddied by rapidly changing ADS-B solutions.
In this article, we’ll put a fresh eye on new models and interfaces, plus offer tips on evaluating an existing vintage model.
BASIC MODE A/C
With the ADS-B mandate roughly four years away, it’s time to evaluate the health, age and supportability of your existing transponder system. It should be addessed as a system because the supporting antenna, cabling and altitude encoder is just as important as the transponder.
As we describe in the sidebar on page 7, if you’ve neglected the required FAR 91.413 transponder inspection and certification (you do know it’s required every 24 calendar months, whether you fly IFR or VFR, don’t you?), now is the time get the aircraft to a shop for an evaluation.
If you haven’t replaced a transponder in a while, you might be surprised at the advances in even basic models. Few manufacturers still offer plain-vanilla Mode A/C transponders. Instead, the trend has shifted to Mode S technology with 1090ES (extended squitter) ADS-B output. And even the few models that don’t have ADS-B output sport advanced features, potentially reducing installation costs and increasing long-term reliability.
For instance, the Sandia Aerospace STX165 is not only designed for tight panels (it can drop into a standard 3-ATI instrument cutout), it also has an integral Mode C altitude encoder, which is certified to 35,000 feet. The encoder can feed pressure altitude data to other onboard systems over the STX165’s serial databus.
When installing an ADS-B system (which will likely require pressure altitude input), shops need to evaluate the health of the altitude encoder, as an aging model might not be up to the task. The STX165 solves the dilemma, while also simplifying the interface. It references pressure altitude by connecting directly to the aircraft’s static system.
This means the aging static lines that snake through the airframe to the old encoder can be removed. These lines are often a source of leakage, so reducing the number of lines and fittings is a good thing.
You can even advance the interface with Sandia’s $350 STP78 temperature probe. The sensor provides an input to the transponder for displaying density altitude, icing alerts and temperature readout.
The STX165 has a simple feature set that consists of dual rotary function knobs, a dedicated VFR squawk button, ident button, plus it has a sunlight-readable and backlit LED display. At $1850, we think the STX165 is a good value for an entry-level upgrade.
BendixKing still makes the KT76C (built to order), a digital model that made its debut when Cessna revived its single-engine airplane line in the late 1990s. The KT76C—which uses surface-mount circuit board technology—(it still uses a cavity tube, despite having a digital front end) is an easy replacement for the mechanical KT76A. It can use the existing wiring and the same mounting rack.
On a side note, the cavity tube in analog transponders is the high-cost component associated with the set’s power output. It generates heat, huge amounts of voltage and will inevitably fail. It pays to use caution when buying a used transponder. We suggest first sending it through a careful bench evaluation—paying close attention to the health of the cavity—by a shop you trust.
Garmin dropped its entry-level analog GTX320A transponder, but still offers the digital GTX327. We like that it has a short chassis, making it versatile in panels that have limited clearance behind the radio stack, or when mounting it outside of the center stack.
The GTX327’s reliability has been good, although we’re hearing of function key failures on units that have been in service for a long time. Flat-rate factory repair is around $600.
The GTX32 is the remote version of the GTX327. It can be channeled from the GTN750 touchscreen navigator, eliminating the need to mount the transponder in the radio stack.
With an RS232 serial data interface, the GTX327/32 interfaces with the GNS and GTN navigators, automatically going into airborne and ground mode, while automatically starting and stopping a flight timer on the takeoff and landing rollout.
But what we really like about the GTX327/32 is its enhanced compatibility with Garmin’s GDL88 and GDL84. These UAT ADS-B transceivers don’t require remote control panels because they interrogate the transponder and communicate with it through the serial databus, automatically keeping both the ADS-B and Mode A transponder codes in sync. Some other serial bus-equipped models will work with the GDL88 and GDL84, but you’ll need to check with your installer to ensure full compatibility.
Want ads-b with that?
If you do, the market is flooded with 1090ES ADS-B Out transponders. Check out the ADS-B buyer’s guide in the June 2015 issue of Aviation Consumer. The choices are overwhelming, although a choice may be easier when you consider which equipment will be interfaced with the transponder. Think long-term, in terms of software and brand compatibility.
The first step is to decide what you will use for an approved ADS-B WAAS position source. WAAS position is an important piece of ADS-B data required for a 1090ES transponder’s data output. That is, if the transponder doesn’t have its own GPS receiver. More on that evolving trend in a minute.
The software and databus configuration in Garmin’s GTX330ES (and remote GTX33) 1090ES ADS-B transponder is based on an architecture that includes its own GNS530W/430W and GTN-series WAAS navigators, although there is compatibility with Avidyne’s IFD540 and IFD440 GPS. These navigators are designed to drop into a GNS530W/430W installation, so it’s logical they can work with a GTX330ES.
Still, while cross-brand interfaces like this may work today, they are vulnerable to future software incompatibility. That makes a good argument for sticking to one brand.
In our estimation, Avidyne’s AXP340, BendixKing’s KT74 and the Trig Avionics TT-series ADS-B transponders could be moving targets when it comes to take-it-to-the-bank long-term compatibility with Garmin’s navigators. They work now, but should Garmin tweak its GNS software—leaving a void in the interface—it will be up the manufacturers to ensure continued compatibility.
Avidyne told us its AXP340 has an AML STC (approved model list supplemental type certificate) which includes the IFD540/440 and the GNS530W/430W as approved position sources, but it won’t work with the GTN750/650. Avidyne’s AXP322 remote ADS-B transponder will be added to that approval list in the near future. It is designed for display on and channeled by the IFD540/440 and is currently in the certification process.
Scotland-based Trig Avionics was an early player with its line of 1090ES models, including the space-saving TT22 and the FDL-1090-TX model it makes for FreeFlight Systems. These transponders are also compatible with Garmin GNS WAAS navigators for position sourcing. Like the KT74, the rack-mounted Trig TT31 transponder can work in an existing KT76A/C installation, but plan on additional wiring for piping in the GPS data—hardly plug-and-play—for which you’ll pay.
As we’ve recently reported, several new multifunction ADS-B products include transponder functionality as standard, plus built-in WAAS GPS and the ability to receiver and display ADS-B weather and traffic.
The first with the most complete and certified all-inclusive rack-mounted solution is L-3 Aviation with the Lynx NGT9000. This is a 1090ES model equipped with an internal WAAS GPS receiver, a dual-band ADS-B traffic and weather receiver, plus a color touchscreen multifunction display.
L-3 doesn’t like to label the Lynx 9000 as a transponder. Instead, it’s marketed as an ADS-B solution with multifunction capability, including a mandate-compliant 1090ES transponder. Still, the NGT9000 replaces the existing Mode A/C transponder in the radio stack (so we call it a transponder), and the system is available in no fewer than four configurations at different price points.
The $8300 base model has a dual-band ADS-B receiver for displaying FIS-B weather, plus ADS-B traffic. There is also a Diversity model (interfacing with top and bottom antennas), plus a model with an integral active traffic alert processor, or TAS. Starting at $10,651, the NGT9000+ can use an existing L-3 Skywatch TAS antenna (the L-3 product has been sold off and is no longer available through L-3), eliminating the need for a remote Skywatch TAS processor. In our trials, we found that the NGT9000 has an easy to manage feature set and a good display.
The flagship NGT9000D+ has TAS and Diversity, plus an eye-widening $13,384 price tag. All of these features could make good sense for higher-end aircraft, but the high price is questionable for basic ones, in our view. We covered the Lynx product line in detail in the April 2015 issue of Aviation Consumer.
Future models
There could be good reason to hold off on a transponder upgrade, given the recent announcements from Appareo and Sandia—both with ADS-B transponder solutions catering to the lower end of the market.
First, Appareo, with the $3500 WAAS-equipped Stratus ESG rack-mounted 1090ES transponder. Currently undergoing FAA certification, the ESG solution is targeted at federated panels (with a mix of brands) that might not have a mandate-approved WAAS GPS. Additionally, Appareo says the ESG will come with mostly everything a shop will need to complete a mandate-compliant retrofit, including a WAAS GPS antenna—no hidden costs.
We hoped the ESG would have an integrated altitude encoder, but it doesn’t. It will, however, accept both Gray code and serialized pressure altitude from a variety of altitude encoders. We’ll look at that market in an upcoming issue.
The ESG is also designed to interface with the popular Stratus and Stratus 2 portable ADS-B receivers, piggybacking with the transponder for receiving power and its GPS signal. This means the Stratus receiver can be remotely mounted, rather than placed on the glareshield.
The ESG doesn’t have a lot of gee-whiz functionality, but instead brings a more utilitarian feature set, including an LED display, push-button squawk code entry and an automatic VFR button.
Sandia is also working on an all-inclusive model—the STX360. Unlike every other ADS-B transponder, the STX360 has a built-in 978 MHz UAT transceiver, rather than 1090ES. This means it isn’t a player for high-flyers. It can display textual FIS-B data and ADS-B traffic targets on its OLED screen. The transponder will also be equipped with a wireless output for displaying weather graphics on tablet computers. The downside? It lacks an internal WAAS GPS receiver, although Sandia said it is planning on a future GPS solution and a remote model to interface with third-party EFIS. Pricing is expected to be below $3500 when the STX360 is released early next year.
Decision time
When it comes to transponders, one size does not fit all. Our advice is to carefully consider the transponder as you plan your ADS-B upgrade. That’s easy if you plan to fly above 18,000 feet because you’ll have no choice but to buy a 1090ES ADS-B model. For basic, non-ADS-B Mode A/C functions, we favor Sandia’s STX165 for its generous features and low price. Shops we spoke with report a straight-forward installation process and good reliability.
When planning a 1090ES transponder upgrade, we think the existing WAAS GPS navigator should have some influence in the decision. Are you comfortable that a third-party transponder will have long-term compatibility with the market-dominant Garmin navigators? While we have confidence that long-established and proven companies like Trig Avionics and Avidyne have the know-how to keep up with changing compatibilities, Garmin has made it clear that it designs products to work primarily in its own architecture. Shops know this and the ones we talked with reiterated that they don’t want to be left holding the money bag should an interface it installs today is abandoned down the road.
If you already have a Garmin GTN750 or 650, our top pick is the GTX330ES (or remote GTX33 if you’re out of panel space). For G1000 (WAAS) panels, the GTX33 is perhaps the only choice, and only if the OEM has approval in place for your specific model.
Just invested in an Avidyne IFD540 navigator? We think Avidyne’s own AXP340 model is the best choice.
For specialty applications with limited panel space—including some gliders and even helicopters—consider a solution from German-manufacturer Becker Avionics. It makes a line of power-saving comm and transponder models designed to fit in 2-inch instrument cutouts.
Last, the safest solution for sure-thing long-term compatibility is a transponder that has standalone ADS-B compatibility, with its own WAAS GPS. If you don’t want to drop the big bucks on L-3’s feature-rich NGT9000, we think the self-contained and budget-focused Appareo ESG transponder is a solution worth waiting for.
