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Garmin ADS-B Academy

Common Questions about ADS-B

What is ADS-B?

ADS-B, or Automatic Dependent Surveillance-Broadcast, is a new technology that allows air traffic controllers to see traffic with more precision than ever before. Instead of relying on decades-old radar technology, ADS-B uses highly accurate GPS signals. As a result, ADS-B works where radar often doesn’t — even in remote areas or mountainous terrain. And because it can function at low altitudes and on the ground, it can also be used to monitor traffic on airport taxiways and runways. Air traffic controllers aren’t the only ones who will see the benefits of ADS-B, though. Aircraft with certain equipment can also receive ADS-B traffic and subscription-free weather information while in flight over the U.S.

How does ADS-B work?

Under the NextGen Air Transportation System and Single European Sky (SES), properly equipped aircraft will broadcast their identity, position, track, speed and other vital data via what’s called ADS-B “Out” technology. Air traffic control ground stations and ADS-B “In” equipped aircraft receive this information once every second. These ADS-B ground stations are broadcasting traffic information – and subscription-free weather in the U.S. – back up to properly equipped aircraft in the service area for display in the cockpit.

What are the benefits?

Air traffic controllers will be able to reduce congestion, noise, emission and fuel consumption through more efficient routing and resource management. Because the system has the ability to provide pilots access to detailed traffic information, ADS-B also represents a leap forward in pilot situational awareness and will greatly enhance the safety of all those in the air.

With optional ADS-B “In” equipment, like the GDL® 88 series for certified aircraft and GDL 39 portable ADS-B receiver, properly equipped aircraft can also receive highly accurate traffic information directly from other aircraft and ADS-B signal corrections. In the U.S., they can also access graphical NEXRAD radar information, as well as METARs, TAFs and other subscription-free aviation weather information.

When should I equip for ADS-B?

In the U.S., if you operate in airspace that currently requires a Mode C or Mode S transponder, you’ll need to be equipped with ADS-B “Out” by 2020.

In the U.S., if you operate in airspace that currently requires a Mode C or Mode S transponder, you’ll need to be equipped with ADS-B “Out” by 2020. This includes Class A, B, or C airspaces, Class E airspace at and above 10,000 ft MSL over the 48 contiguous United States and the District of Columbia, and Class E airspace over the Gulf of Mexico from the coastline of the U.S. out to 12 nm and above 3,000 ft MSL. Even if you don’t fall into one of these categories, you’ll still need an ADS-B “Out” solution if you find yourself flying from the surface up to 10,000 ft MSL within 30 miles of most primary Class B airports.

Australia — All Australian aircraft operating at or above FL 290 must be equipped with 1090 ES ADS-B “Out” functionality by Dec. 12, 2013. All aircraft that operate in Class A, C, or E airspaces extending 500 nm to the north and east of Perth Airport must be ADS-B “Out” capable by Feb. 4, 2016. Any IFR-capable aircraft placed on the Australian aircraft register on or after Jan. 1, 2014 will need to be compliant by Feb. 6, 2014, and any aircraft placed on the Australian aircraft register before Feb. 6, 2014 will need to be compliant by Feb. 2, 2017.

Europe — All aircraft operating in European airspace must be equipped with 1090 ES ADS-B “Out” with a Diversity Mode-S transponder by Jan. 8, 2015, for new aircraft, and Dec. 7, 2017, for existing aircraft. This only applies to aircraft>12,500 lbs or max cruise>250 kts TAS.

Hong Kong — Beginning December 12, 2013, all aircraft flying along PBN routes L642 or M771 at or above FL290 and within the Hong Kong FIR need to be installed with a complaint 1090 ES ADS-B "Out" solution.

Singapore — Beginning December 12, 2013, aircraft that operate on on select airways and within a select region of the Singapore FIR at FL290 or above will need to have a compliant 1090 ES ADS-B "Out" solution and operational approval from the State of Registry. For details on these requirements visit the CAAS website.

What equipment do I need for compliance?

First and foremost, you’ll need a WAAS position source, such as a GNS 430W/530W or GTN series avionics. This calculates your required position, track, altitude and speed information from signals it gathers from GPS satellites and WAAS signal corrections.

First and foremost, you’ll need a WAAS position source...Next, you’ll need a way to broadcast this information to ADS-B ground stations.

Next, you’ll need a way to broadcast this information to ADS-B ground stations. If your aircraft flies at or above 18,000 ft over the U.S., or anywhere internationally, you will be required to use the 1090 MHz frequency using a Mode S Extended Squitter (ES) transponder — such as the GTX 330 ES.

Aircraft that only fly below 18,000 ft and only in the U.S. can opt instead for a dedicated 978 MHz Universal Access Transceiver (UAT). The 978 MHz UAT frequency will allow you to keep an existing Mode C or Mode S transponder that you may already have. Installing a 978 MHz UAT with ADS-B “In” technology such as the GDL 88 series allows you to view Traffic Information Service-Broadcast (TIS-B) and Flight Information Service-Broadcast (FIS-B) information on a compatible flight display.

Why should I pay for ADS-B “In” if I’m only required to have “Out”?

If you only equip for ADS-B “Out,” you’re investing a lot of money without seeing any real benefit in the cockpit. You’re simply transmitting your position to ATC and other aircraft in your vicinity. But by adding an ADS-B “In” datalink receiver and a compatible cockpit display, you’d also be able to view highly accurate traffic data from other aircraft and ADS-B ground stations, as well as subscription-free weather information (U.S. only). You’d gain valuable situational awareness and safety with minimal investment versus what you’d need for ADS-B compliance anyway.

Where are ADS-B ground stations operational?

In the U.S., nearly 400 ADS-B ground stations were completed and operational by mid-2012, with most of the rest — totaling more than 700 planned stations — expected to be up and running by early 2014. The graphic below illustrates where ADS-B is up and running. In the areas highlighted in blue, you can already start taking advantage of ADS-B’s datalink traffic and subscription-free weather services if you’re equipped with an ADS-B “In” solution.

Why should I consider a dual (diversity) antenna installation for my ADS-B solution?

Antenna diversity technology configures your aircraft with both top- and bottom-mount antennas to reduce the potential for antenna “shading,” which helps prevent target drop out during turns and maneuvers. An optional top-mounted antenna also comes in handy during ground operations, when a bottom-mount mount antenna might not have clear line-of-sight to receive ADS-B ground station signals or transmissions from other participating aircraft.

I already have an active traffic system, how will this work with ADS-B?

For those who fly outside of the U.S., an active traffic system will still be the only source of traffic information you can receive. In the U.S., adding ADS-B datalink traffic capability can provide you with the most comprehensive traffic picture possible. Our GDL 88 series integrates with active traffic systems. It takes in traffic data from ADS-B sources and active traffic systems (TCAS/TAS/TCAD) then correlates the data. If a single target is being provided by multiple sources then the source with the best integrity is used to display the target. Having an active traffic system will give you traffic data when operating in uncontrolled airspace.

If I am receiving and displaying ADS-B “In” datalink traffic, why do I need an active traffic system?

When paired with an ADS-B “In” solution like the GDL 88 series, an active traffic system like the GTS 800 series provides the most complete traffic picture possible.

During the transition to ADS-B, those that haven’t yet equipped will not be transmitting their information via ADS-B “Out.” In the U.S, when you’re flying outside the range of a TIS-B ground station uplink, you will not see these targets on your flight display. Thus, you’re not getting the entire picture until everyone becomes equipped in 2020. When paired with an ADS-B “In” solution like the GDL 88 series, an active traffic system like the GTS 800 series provides the most complete traffic picture possible.

How can I tell if I have an appropriate high-integrity WAAS/SBAS position source?

Both the GNS 430W/530W and GTN series have the WAAS/SBAS GPS technology capable of meeting the requirements of an ADS-B “Out” position source. Older, non-WAAS/SBAS GNS 430/530 navigators can be upgraded to the WAAS/SBAS version that has the technology. In addition to helping you reach ADS-B “Out” compliance, WAAS/SBAS navigation offers additional benefits like being able to fly GPS-guided LPV glidepath instrument approaches down to as low as 200 ft where approved. If you’re unsure whether your GNS is equipped with WAAS/SBAS, just watch the initial splash screen during the start up. If a “W” is displayed after the model number, it is in fact a WAAS/SBAS version.

GNS 430 Non-WAAS

GNS 430 with WAAS

How can I tell if my GTX 330, GTX 33 or GTX 23 is an Extended Squitter (ES) transponder and/or meets the current requirements for ADS-B “Out”?

To understand if your GTX 330 is an Extended Squitter version, pay attention to the splash screen when your avionics are being powered on. You'll see either "GTX 330" or "GTX 330 ES." This should make it clear which version you have. The same is true of the remote GTX 33. It should be noted that the GTX 23 is only available with an Extended Squitter.

GTX 330

GTX 330, Extended Squitter version

If you do not have an Extended Squitter version, an upgrade is available starting at $1,200. For customers with an existing Extended Squitter transponder, an update to meet the ADS-B requirements will be free of charge. However, some labor and handling charges may apply. Your Garmin dealer can make arrangements for this upgrade.

How does the GTX ES Upgrade Process work?

Existing GTX ES transponders need to have their software updated before they are ADS-B compliant. You can get this upgrade right from your authorized Garmin dealer. Upgrades from a non-ES transponder to an ES transponder will require your dealer to ship the unit back to Garmin for the upgrade.

Can the GPS position from the GDL 39 feed other apps?

Other apps on your phone or tablet can use the GPS position from your GDL 39, which is often more accurate and reliable than the GPS data derived from built-in GPS receivers.

Yes. Other apps on your phone or tablet can use the GPS position from your GDL 39, which is often more accurate and reliable than the GPS data derived from built-in GPS receivers.

What is the status of ADS-B “In” for countries outside of the U.S.?

At this time, ADS-B “In” is only a service provided in the U.S.

What are the display compatibilities with ADS-B “In”?

Please consult the “Compatible Devices” tab on our GDL 88 and GDL 39 product pages.

Can I use the GDL 39 outside of the U.S.?

The the GDL 39 will act as an enhanced GPS position source for your compatible device outside of the U.S. However, ADS-B “In” services like subscription-free weather and datalink traffic are not available outside of the U.S.

Will the GTX 330 ES, GTX 33 ES, or GTX 23 ES transponders display traffic via the FAA’s TIS-B ADS-B uplink?

The ES transponders currently have the capability to uplink the FAA’s TIS-A traffic (consult the question below regarding differences between TIS-A and TIS-B traffic). There are currently no plans to update the transponder to uplink from TIS-B.

How does my transponder interact with the GDL 88?

ADS-B requires that both your Mode-C or Mode-S transponder and your GDL 88 output the same Mode 3/A “squawk” code and SPI (ident) code. With certain installations, this could mean that you have to enter the squawk code in two different places. Garmin mitigates the need for this using several methods. First, if the transponder has a compatible interface, the GDL 88 will retrieve the correct squawk code from the transponder. If the transponder doesn’t have a compatible interface our patent-pending technology allows the GDL 88 to automatically detect and synchronize with the transponder’s Mode 3/A “squawk” code and SPI. In most cases you’ll be able to retain an older transponder that may not have any wired interfaces at all.

Are advanced features like TargetTrend available for display on the GNS 430W/530W series?

Because of its advanced nature, TargetTrend requires a higher-speed speed connection and more processing power than the GNS series is capable. You can find a complete listing of display compatibilities on the “Compatible Devices” tab of the GDL 88 product page.

Will the GDL 88 receive TIS-A traffic like a GTX 330 ES transponder?

The GDL 88 receives TIS-B traffic service and does not receive TIS-A traffic.

Will the GDL 39 receive TIS-A traffic like a GTX 330 ES transponder?

The GDL 39 receives TIS-B traffic service and does not receive TIS-A traffic.

What’s the difference between TIS-A and TIS-B?

TIS stands for Traffic Information Service. With TIS-A, ATC radar information is collected on the ground and then uplinked to equipped aircraft nearby (known as “Clients”) via ground radar uplinks. Uplinks can occur only when the radar is pointed at the aircraft, so the amount of information transmitted is necessarily limited. TIS-A is currently available in the U.S. at over 100 Terminal Area Secondary Radar Surveillance Areas and is slowly being phased out in favor of ADS-B.

When the ADS-B ground infrastructure build out is complete in the US, there will be close to 800 ground stations broadcasting TIS-B data.

With TIS-B, ATC radar information is collected on the ground and then ADS-B ground stations uplink this information to equipped aircraft with an ADS-B “In” receiver capable of receiving ADS-B data on 1090MHz. When the ADS-B ground infrastructure build out is complete in the US, there will be close to 800 ground stations broadcasting TIS-B data.

What happens if I have weather from both ADS-B and a datalink provider like SiriusXM onboard?

The interface in our avionics allows you to view weather data from both sources individually via the weather menus. In parts of the menu where only METARs and TAFs are displayed (like the waypoint information pages), the data source that is the most recent is displayed and the source denoted for reference.

Will the GDL 39 meet ADS-B “Out” requirements?

It does not meet ADS-B “Out” requirements, but can be used as a convenient and affordable way to increase situational awareness in the cockpit.

How many antennas are required with a GDL 88D (diversity) and GTX 330D ES (diversity) installation?

This specific installation requires 2 antennas on the top of your aircraft and 2 antennas on the bottom.