View Full Version : Does ADS-B In require having ADS-B Out?

Ron Lee
11-14-2010, 05:28 PM
Can an aircraft system (TBD hardware...possibly handheld) receive TIS-B and FIS-B (especially weather) without having ADS-B Out working on that aircraft?

11-14-2010, 08:29 PM
Yes, it appears this is becoming the trend, at least for now. Some stations will not broadcast the TIS-B and FIS data unless it receives a request.

11-14-2010, 09:41 PM
Booo... if true

That is not what FAA advertizes:

"FAA Aviation Safety
ADS-B Frequently Asked Questions

Why is the FAA deploying ADS -B technology?

The Federal Aviation Administration (FAA) is transforming air traffic control from a ground-based network to a satellite-based system called ADS-B (Automatic Dependent Surveillance–Broadcast). As the cornerstone of the Next Generation Air Transportation System (NextGen), ADS-B will increase the safety and efficiency of the National Airspace System.

What is the difference between ADS -B Out and ADS -B In,and what will I need to equip?

ADS-B Out is the ability to transmit information out of the aircraft to ground stations and to other equipped aircraft. ADS-B In is the ability of the aircraft to receive information from other transmitting aircraft or the ground infrastructure. The proposed ADS-B rule would mandate ADS-B Out only in specific airspace (see #3). While the FAA wants the system to evolve to
its maximum potential, at this time, the FAA is not mandating ADS-B In. The ADS-B Traffic Information Service–Broadcast (TIS-B) and Flight Information Service–Broadcast (FIS-B) will be available free to anyone who chooses to equip with ADS-B In capability."

NavWorx has both receivers (in) and Transceivers (in&out).

11-14-2010, 10:45 PM
We have a NavWorxs ADS-B in box linked to AFS efis. Flying 2-6 times a week around Houston, x-countries to FL, MN, and lots of others.... I've never once gotten a traffic symbol. The simulator mode works perfect, which leads me to believe that if you aren't transmitting, you'll not receive.

Sucks really. Looks like I have to upgrade to a Mode S (GTX330) and a ADSB Transceiver to get real traffic.

11-15-2010, 12:35 AM
You do not need ADS-B out to recieve ADS-B in transmissions.

If you have an applicable reciever, you can plug the recieved signal into an applicable cockpit display, and voila!.

11-15-2010, 06:45 AM
Yeah, Ron. You need it.

The FAA wrote that into their mandate and it chaps my ***. They won't "broadcast" the ADS-B data openly. Your system has to transmit to them first, then they'll share data with you.

On a side note, I know that's how it works if you're the only airplane in the area. You have to transmit to open the faucet. But I don't know how it works with other aircraft in the area who do have a transmitter. It might be possible to leech their data signals for your own use.

But the correct answer is, yes. It's a requirement. The EAA and AOPA have been fighting to get that changed, but I don't think they're having much success.


Ron Lee
11-15-2010, 07:30 AM
This sounds shortsighted if true. With the inexpensive systems available today, if they could process the "IN" data (primarily traffic and weather), I suspect that many people would so equip. I was considering a certain unnamed system IF it did receive and process that data.

Yes I am still opposed to the ADS-B Out mandate, but FREE weather primarily and traffic secondarily would be great.

PS..the "if true" caveat does not impune the comments made above mine. Just a standard caveat.

11-15-2010, 07:48 AM
I had a discussion with Bill Moffit from Navworx about this. According to Bill, the way the FAA is operating the system, you will need to have ADS-B out to ensure you will receive traffic near you. Each ADS-B ground station controls a very large volume of airspace. FAA is not broadcasting all of the traffic in that airspace, they are only broadcasting the traffic within a small cylinder around those aircraft they receive a transmission from (something like +/- 3500 ft and 7 mile radius from the ADS-B out equipped aircraft).

So if there is only one target in the volume transmiting via ADS-B out, and he is far away from you, you will not receive any meaningful traffic info via ADS-B in. If he is near you, you WILL receive some relevant traffic info depending on how far he is. To me, the more appropriate term for this might be NARROWCAST rather than BROADCAST. Weather info is truly broadcast, so according to Bill, the only reason to buy the RECEIVER ONLY is to get weather, you need the TRANSCEIVER to get meaningful traffic info.

Oh and by the way, since ADS-B has GROUND stations rather than satellites, you need to be airborne in most places to receive the signal. No checking weather on the ground prior to launching on that long X-country and maybe no traffic at pattern altitude and below in many places. At least until all aircraft are equipped and aircraft to aircraft transmissions become the norm.

11-15-2010, 09:22 AM
In terms of avionics, ADS-B "In" is the ADS-B "Out" system with the added ability to support air-to-air ADS-B application like self-separation from other aircraft in terminal airspace or on instrument approaches.

It's true that UAT TIS-B systems will only broadcast traffic to aircraft that are transmitting their position over UAT. It's filtered to only provide targets within a certain range and altitude of aircraft transmitting their position via UAT. As of now just about all of that traffic comes from ATC radar, and if TIS-B sent every target seen by the radar, the link would get clogged - hence the filtering.


Dave S
(former DOT ADS-B engineer)

Ron Lee
11-15-2010, 10:29 AM
OK, I will give up on traffic info. I suspect that it will hardly be close to 100% for two reasons:

1) Many people will not equip with ADS-B Out
2) A major reason for ADS-B Out is to save the FAA money by getting rid of radars. With no skin paint info, there will be lots of planes that will be around that you won't see on your ADS-B In screen.

Conclusion: ADS-B traffic will not be a reliable traffic alerting system for GA.

So my real need for ADS-B In is free weather. If that is broadcast, why not get it without needing ADS-B Out?

11-15-2010, 05:38 PM
It sounds like you chaps are discussing TIS-B not ADS-B. You do not need to transmit your ADS-B position to get ADSB data. Once the ADS-B transmission leaves the antenna on the aircraft, it can be picked up by anyone with an applicable reciever.

11-15-2010, 07:16 PM
It sounds like you chaps are discussing TIS-B not ADS-B. You do not need to transmit your ADS-B position to get ADS-B.
I believe the Australian implementation of ADS-B is quite a bit more straightforward than what the FAA's plan.

In the States TIS-B is a part of the initial ADS-B program partially to be an incentive to equip early and get non-ADS-B traffic from ATC radar, and partially because we're fielding two separate datalinks - UAT and Mode S. We'll need TIS-B or ADS-R to see traffic operating on the other datalink.


11-18-2010, 11:51 PM
It sounds like you chaps are discussing TIS-B not ADS-B. You do not need to transmit your ADS-B position to get ADSB data. Once the ADS-B transmission leaves the antenna on the aircraft, it can be picked up by anyone with an applicable reciever.

True except here in the US the TIS-B will not go "out" from the ADS-R (ground station) unless it picks up a transmission from a UAT "out" (one of two types of ADS-B signals the other being a 1090 MHz ADS-B signal). The ADS-R will send a signal to your ADS-B "in" receiver if there is someone with an ADS-B "out" signal in the area. My understanding is that the "out" signal has to be a UAT signal not a signal from a 1090 MHz ADS-B transmitter. The NavWorx is a UAT. UAT is serviceable up to 18,000' but it is also the only one that gets weather. The 1090 MHz ADS-B does not have weather capability but is what the airlines have to use go into the "above 18,000' altitudes." Go figure, the least universal of the two has the most features. The UAT gives traffic and weather here in the USA. The system the airlines use (1090 MHz ADS-B) only gives traffic but is usable at all altitudes of flight and in all countries that use ADS-B.

I have the UAT "in" and "out" and fly around Houston. I have seen a wee bit of traffic from it but most of what I see is from my GTX 330. I am yet to see any weather even when there is weather in the vicinity. That MAY be a result of the EFIS not recognizing the weather signal from the UAT. It is a topic that is "under investigation." :D

11-19-2010, 01:43 PM
From discussions with the FAA last week:

Different answer for traffic and weather.

The Weather picture is likely going to be available to anybody with a receiver. The FAA seems to recognize that this is such a safety benefit they do not want to make it "conditionally" available. Also, unlike traffic, there are no safety implications to receiving weather without being an ADS-B system "Client".

For traffic, the answer is different. In the current version of the ADS-B ground system anybody who is transmitting an ADS-B out signal with some integrity data included will get a traffic picture. This is to accommodate people who equipped to earlier standards that no longer meet the rule). If the system you are using is uncertified it should be transmitting integrity data at "zero" and the ground system reserves this as a "faulty ADS-B code" and you will be ignored.

In the next software version of the ground system (probably mid 2011) they will only transmit traffic to a an aircraft that is transmitting valid ADS-B integrity and design assurance data (certified radio and certified WAAS GPS). The data they send is centered around the position you reported (15 miles diameter, 3500 feet above and below your reported position). They need to make sure you are not using a bad GPS position (either in your position report to them, which could pose a danger to you or other traffic that would get a report of your position) or in your display of the report they send you. If your GPS position is "off" the traffic display will be "off" by the same amount. Not Good.

If you rely on a properly equipped aircraft to trigger the traffic message for you, you have two real risks:

1 Whatever GPS you are using to display the traffic may be off by a bit so your own-ship position relative to the traffic display will be off by the same amount

2 The system sends a 15 mile radius picture centered around the other guy. If you are (say) 15 miles away form him, you will see traffic that is between you and him, but no other. This is really bad - you are seeing traffic so you think you are getting a full picture but you are not.

This is all about integrity and accuracy of position determination for your own aircraft. Not all GPS's are created equal - this is why the FAA wants certified position sources. Certification is the only way for them to know that you have a good enough GPS.