ADS-B and Experimental Aircraft

Is the future now?


An illustration by the FAA describing how ADS-B works. Note how each aircraft can receive information from another, and how both send information to satellites as well as ground stations where air traffic controllers can see the traffic on their screens.

The portable NavWorx ADS-B receiver can sit on the glareshield and be wired via the panel into several different multifunction displays. Here it is attached to a Chelton.

To all of you builders out there, if you haven’t already designed and constructed your instrument panels, please pause. Just give me 5 minutes of your time to explain an acronym that the FAA has been kicking around for a decade or so, because, finally, it looks like ADS-B has come to us, the Experimental aircraft crowd.

Automatic Dependent Systems-Broadcast (ADS-B) is a means of solving air traffic control separation issues in the U.S. and around the world in a manner that you’re probably going to like-persona a persona-airplane to airplane. Heres how it works. You have a box with a universal access transceiver (UAT). They have a box with a UAT (or a 1090 extended squitter [1090ES] if they routinely operate in the rarified air of Class A). The boxes talk to each other, telling each aircraft where the other is and displaying pertinent information including trajectories, apparent track and altitude. The pilots of the aircraft use this information and any other information that might come from other transponder-equipped aircraft in the vicinity to keep from swapping paint-while both airborne and on the ground.

An illustration by the FAA of ADS-B equipped traffic working a merge-and-space algorithm into the Louisville, Kentucky Airport.

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Another close-up illustration of how merge-and-space software can sequence traffic from different quadrants, all on constant power descents. The fuel savings, according to UPS, are significant.

The hardware necessary to turn existing Avidyne multifunction displays into ADS-B displays (note the top and bottom antenna array, which is also necessary for the Ryan active traffic display system).

Whither ATC?

Where are air traffic controllers in this perfect scenario? They get the 1090ES and the UAT signals through satellites and their series of ground stations. They also receive the Mode C or S transponders, and they can still separate traffic the old-fashioned way. But the hope is that at least on the VFR front there will be less need for ATC to be in the VFR advisory business, because pilots will be able to see and avoid their own traffic on the same level.

Why is this better than the TIS (traffic information system) you can get with a Garmin GTX 330 or Mode S transponder? Two words: coverage and weather. TIS only works where there is radar, and sometimes not even there. Plus, it comes up to us from the ground as a repeater of what ATC sees, with the resulting delay in display. Five-minute-old traffic information occasionally even paints a ghost image of your airplane as traffic right behind you at a similar altitude.

ADS-B doesn’t do that. You get the information right from the other airplane as the transceiver talks to other transceivers in the area, and from satellites. The ground sees what you see, and it doesn’t need line-of-sight limited radar to work.

The Garmin GTS 850 enables Garmin products to have ADS-B active and passive traffic surveillance.

All This and Weather, Too

A lot of readers may be considering (or may have already invested in) either a full TCAS alerting system, or the Zaon XRS or MRS passive traffic advisory systems, and these are good systems that don’t rely on radar coverage. But they are missing the second component that makes ADS-B attractive: weather. With ADS-B, ground stations broadcast FIS (Flight Information Service) including Nexrad imagery every 2.5 to 5 minutes, METARS every 1 minute, TAFs, AIRMETS, SIGMETS and Special Use airspace information as it becomes available-free. These ground stations now carpet the East Coast of the U.S., and are being rolled out to cover the U.S. completely from 5000 feet MSL up by 2013. In most areas aircraft will be able to receive FIS from 2000 feet AGL. Certain areas, such as the U.S. Gulf Coast, will receive FIS-B from as low as 500 feet to aid helicopter and seaplane traffic that routinely works at low levels as the aircraft transit the numerous oil rigs in the region.

The Garmin GTS 820 package includes a four-channel GPA 65 power amplifier/low noise amplifier (PA/LNA) to be remotely installed near the top directional antenna. Its purpose is to boost antenna performance while minimizing power consumption, thus enhancing system efficiency.

But don’t take my word for how well it works. Look at the stats. The Capstone 1 project, run by the FAA nearly a decade ago, equipped all Alaskan aircraft operators with ADS-B transceivers (the Garmin GDL 90) and either Chelton or MX200 PFD/MFDs. Accidents dropped by 40% during the study period. There is no question that the terrain avoidance software that came along with the MFDs contributed to the reduction in accidents, but there is also no question that mid-airs were reduced significantly, too.

UPS equipped its fleet and saw runway incursions decrease at its Louisville, Kentucky, operation. The company also used the ADS-B to help create Constant Descent Profiles, software that could be uploaded to the aircraft to help them merge and self-space while approaching Louisville on nightly runs. The Constant Descent software meant the throttles came back once, and then, at a steady rate, the aircraft were all neatly dovetailed into the pattern to land. The fuel savings? Try 30% out of the box. Even the air traffic controllers, who now hardly have to control traffic coming into Louisville at night, were amazed. Imagine how that would work for all the IFR traffic in the world. Wed increase efficiency and reduce both costs and noxious emissions all at once. The airlines are begging for this kind of technology right now, and Boeing, at least, is said to be delivering airplanes today that already have the technology on board, waiting to be turned on.

Embry-Riddle Aeronautical Universitys entire fleet of aircraft were equipped with the same transceiver in 2003/2004 and has been recently reaping the benefits of the added safety that newly activated ADS-B ground stations in Florida bring, with the advent of the FIS-B products.

ADS-B and TIS-B traffic are depicted differently on an Apollo MX20 as the aircraft flies through the Anchorage Bowl in Alaska. The ADS-B targets display aircraft type and N-number as well as track, climb or descent and differential altitude.

ADS-B traffic displayed on a Garmin GPS 495 portable unit.

Ask the Man Who Owns One

Finally, lets hear from an early adopter, Tim Olson, an RV-10 builder and pilot who is now operating with NavWorx ADS600, a remote mount Universal Access Transceiver (UAT) designed to DO-282A standards. The product is non-TSOd and displays ADS-B and TIS-B traffic, as well as FIS-B weather products on compatible displays. Olson says, The ADS600 comes with a DB37 low density connector containing various interfaces, including RS232 for ADS-B data in and out, RS422 for a GPS time-mark signal for external WAAS GPS navigator connection (eliminates the need to use our internal GPS, and hence having to connect a separate GPS antenna), as well as an optional ARINC 429 interface for connecting to devices that display ARINC 735 TCAS traffic (namely the Garmin 430/530 and GNS 480).

After testing the NavWorx portable box in the fall of 2008 and discovering that it was practically plug-and-play with his Chelton system, Olson asked NavWorx to create a bit of software that would allow him the best of both worlds. Ive been flying the WSI weather and I enjoy it and find it a great system. I want to keep my satellite weather, he explained. So we worked out a special TIS pass-through so I could have both. We know that they [the FAA] is decommissioning TIS. NavWorx has figured out how to bring the TIS coverage through the box so you can have either ADS-B or TIS. But the ADS-B coverage available already is surprising. I was flying between Salt Lake City, Utah, and Oregon over remote areas of Idaho, and I was in ADS-B coverage. When near Salt Lake City I was in Mode-S coverage, so the TIS worked. And for the time being with the special interfacing NavWorx set up, I have the ADS-B as traffic only with the WSI for weather. It is the best of both worlds for now.

ADS-B traffic is displayed on a Garmin GNS 530 panel-mount unit.

Stein Bruch, principal of SteinAir, builder of custom panels for many Experimental aircraft, said he gets a lot of requests for information about ADS-B, but when there was only the GDL 90 box (which retails for just under $7000) and few ground stations around the country broadcasting FIS, he was hard-pressed to recommend it. Right now our feeling is that the ADS-B technology isn’t mature enough to offer it, he explained.

Still, hes impressed with the NavWorx box, especially at the roughly $1500 asking price. There are a couple of other EFISes that are ready for ADS-B, Bruch added. GRT Avionics in Michigan and Advanced Flight Systems in Oregon are both working with NavWorx to develop the software interface for the NavWorx boxes. And then certainly the Garmin boxes all have the interface to ADS-B with their own transmitters, and NavWorx interfaces with the portables as well. But all this counts on the FAA to put the ADS-B infrastructure together, and also keep the FIS free to make it a good deal.

Garmin has introduced its new GTS 800 series receivers for its G900X. The systems use Garmins patent-pending CLEAR CAS technology and correlate ADS-B and radar targets for Garmin technology users. The lower-end receivers (800/820) are designed to be traffic advisory services, whereas the high-end system is fully TCAS I qualified. The GTS 800 product receives replies to its interrogations and makes its computations. It then tweaks location data with data received from ADS-B Out-equipped targets, plots the traffic location, predicts collision threats and depicts the information on the traffic display or in synthetic-vision-equipped systems on the PFD. The system also puts out audio traffic alerts that are liable to belt out: Traffic, three oclock, low, less than 1 mile. If that doesn’t get your attention, I don’t know what will. The cost of upgrading a G900X system? The expected price is $9995, $19,995 and $23,495, depending on how powerful a system you want.

The low-level ADS-B relay stations put in place along the Gulf of Mexico to guarantee coverage for low-flying seaplanes and helicopters, as well as high-flying airliners. The real benefit is to those in the middle, who will get good traffic and weather coverage out into the Gulf.

Its About Time

The FAAs timeline for the ADS-B and NextGen projects is admittedly aggressive, but some, including the Aerospace Industries Association (AIA), would like to see even that timeline stepped up. The final rule on NextGen is due out in spring 2010, which is nearly upon us. At that point it will finally be clear which aircraft will be required to be equipped with which technology (UAT and 1090ES), and manufacturers should be quick to follow with transceivers that are more affordable. By 2020 well all be sporting some sort of ADS-B Out technology, and many believe the FAA will keep the FIS in to encourage operators to equip and take advantage of the free Nexrad, airspace and weather information it broadcasts.

If you haven’t committed to some kind of traffic and weather receiving system, it behooves you to at least consider ADS-B as you plan your instrument panel and capabilities. All you need is an EFIS and a transceiver that could cost less than a Mode S transponder. At these lower price points, and with an impending mandatory equipage ruling due out, ADS-B is beginning to make sense.

To read more about the final FAA rule on ADS-B, go to the rule-making docket web site at, under document identification number FAA-2007-29305-0221.1. To locate other documents and comments related to the NPRM, search for FAA-2007-29305.

FIS-B weather information scrolling on the Chelton MFD screen.

ADS-B targets on the Chelton display. ADS-B traffic has more information than standard TIS (terminal information service) targets.

This is the NavWorx ADS-B depicted on a Chelton screen that is installed in a Vans RV-10.


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