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  #1  
Old 12-09-2016, 02:52 PM
tsneidin tsneidin is online now
 
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Default ADS-B TIS-B Client %

My last flight ads-b traffic worked just fine, today no traffic. I received the ads-b performance report for the flight and it shows that I transmitted ~9700 messages to them, no errors or RED flags on the report at all, SIL=3 etc. The TIS-B Client % field is 0.0%. According to the docs TIS-B Client % is:

TIS-B Client %: Percentage of operation time TIS-B data
was provided to the aircraft by the ADS-B ground
system.

So if everything was reporting correctly why didn't the ground stations provide any data? Traffic showed up for my previous flights and the reports shows TIS-B Client % around 100%.

This flight was in central Wisconsin 12/9/2016
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  #2  
Old 12-09-2016, 04:05 PM
BobTurner BobTurner is online now
 
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Well, if TIS-B was zero, either the ground station was malfunctioning, or there was no traffic to report. Remember they only send up traffic within the 15 nm radius, up/down 3500', hockey puck region. Did you see any traffic within that volume?
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  #3  
Old 12-09-2016, 04:15 PM
greghughespdx greghughespdx is offline
 
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Yes, assuming you didn't observe any traffic (with eyeballs), it's likely there was no traffic close enough to you to provide TIS-B data for.

Did you see any other aircraft while you were flying?
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  #4  
Old 12-09-2016, 04:29 PM
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Radomir Radomir is offline
 
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Post the report if you can.. What do you have for IN capabilities configured? It's listed on the report so you can check quickly.. If it's "none" then I suspect they won't send you any traffic data...
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  #5  
Old 12-10-2016, 08:27 AM
tsneidin tsneidin is online now
 
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I'm configured for Both for ads-b in. There was plenty of traffic that should have been showing up, MSN approach vectored me twice for traffic conflicts. Neither the 696 or garmin pilot app had the normal ads-b symbols lit up.

https://drive.google.com/file/d/0B8A...w?usp=drivesdk
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  #6  
Old 12-10-2016, 10:00 AM
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g3xpert g3xpert is offline
 
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Hello Todd,

First a clarification. Some postings above are saying that the presence of traffic in the area you are flying will affect the "TIS-B Client %" value being reported in this report from the FAA. This is entirely incorrect.

Whether or not the ground stations are providing you with TIS-B client services is strictly between your aircraft, ATC radar, and the ADS-B ground stations and has nothing to do with having traffic in the area. You must be in radar contact and must be a valid ADS-B Out aircraft with ADS-B In capability before the ground stations will declare you a TIS-B client and provide TIS-B traffic (Mode C) uplinks.

Notice that this also applies to whether or not you receive ADS-R uplinks, but since you have a GDL39 dual frequency receiver and don't need any help from the ground stations to see ALL ADS-B Out traffic on both 978/1090 Mhz directly (and they know this from your ADS-B Out messages), they don't provide ADS-R uplinks to you.

The meaning "valid ADS-B Out" aircraft has been a moving target. Aircraft transmitting SDA=0 with non FAR 91.227 compliant position sources used to be able to receive TIS-B client services, but early in 2016 the bar was raised to SDA > 0, which made little sense (prior to 2020 which requires SDA=2), but that is what they did. As you know, FAR 91.227 specifies SDA = 2 (and SIL=3), so raising the bar to provide TIS-B services to aircraft transmitting SDA=1 is only on a temporary condition.

Note that this doesn't have anything to do with you since you are transmitting SDA=3, SIL=3, but we bring this up as history since your SDA=3 is a little unusual. As mentioned above FAR 91.227 doesn't say SDA>= 2, it says SDA = 2.

I just looked at the most recent reports from the two G3X EAB aircraft we fly, and both are transmitting SDA=2, SIL=3. One of them has a GTX345R with built-in GPS position source and the other (our RV-7A) has a GTX 45R with GTN 750 external ADS-B position source.

I also looked at an older report with a GPS20A position source connected to a GTX23ES, and it also transmitted SDA=2, SIL=3.

I don't think think there is a problem with you transmitting SDA=3 and the report shows no problem with this, but it is unusual, so not sure if that is affecting whether or not the ground stations provide TIS-B client services to you.

You mention that your 696 and Garmin Pilot displays agree with this FAA report that you are not receiving TIS-B client services. Good to hear since the ground stations send out a list of ICAO addresses that are receiving TIS-B client services every 20 seconds and the GDL39 looks at this list to verify your aircraft address is in the list before telling the displays that your aircraft is receiving these services. At any point that 2 of these updates pass and your aircraft ICAO address is not in the TIS-B client list, the GDL39 tells the displays you are no longer a TIS-B client.

So, lots of words here to say that you "should" have been receiving TIS-B services as long as you were flying high enough on this 36 min. flight to be in radar contact. Was this the case? This is one of the protections in place to make sure there is little chance of someone spoofing the system. No radar contact, no TIS-B client services provided. You say that Madison was vectoring you for traffic, so it sure seems like you should have been in good radar contact, but since this might have been terminal radar approach control, I don't know if this satisfies the radar contact requirements for ADS-B TIS-B services.

In past years it wasn't uncommon to see "holes" in the system when handoffs between ground stations providing TIS-B services would sometimes fail, but the system seems pretty robust these days. On most of our flights the TIS-B Client % is close to 100%.

Thanks,
Steve
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Last edited by g3xpert : 12-10-2016 at 10:52 AM.
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  #7  
Old 12-10-2016, 11:13 AM
tsneidin tsneidin is online now
 
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Default Thank you Steve

Thank you for that helpful explanation. I was flying 2000agl, squawking a discrete transponder code while receiving vfr traffic advisories from MSN approach. At the end of the flight I specifically asked the controller if my transponder was dropping or weird in any way and he replied that it appeared to be working perfectly.

The position source for my Trig Tt-31 is the garmin GPS 20A that I recently installed. I have reports from previous flights where I received traffic perfectly and the SDA was equal 3.
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  #8  
Old 12-11-2016, 12:18 AM
maus92 maus92 is offline
 
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Quote:
Originally Posted by tsneidin View Post
Thank you for that helpful explanation. I was flying 2000agl, squawking a discrete transponder code while receiving vfr traffic advisories from MSN approach. At the end of the flight I specifically asked the controller if my transponder was dropping or weird in any way and he replied that it appeared to be working perfectly.

The position source for my Trig Tt-31 is the garmin GPS 20A that I recently installed. I have reports from previous flights where I received traffic perfectly and the SDA was equal 3.
When I run into intermittent problems, I usually go back through every configuration step, and check the mechanical / electrical connections. I looked at the Trig TT31 manual for compatible GPS sources, and noted that the GPS20A has not been tested (that doesn't mean it won't work.) The GPS20A operates at 9600, I'd check to verify that speed is configured in the Trig. I'm assuming you configured the protocol as Garmin ADSB+. Have you checked if the connectors are tight on each unit, and the pins are properly seated? Are you using an approved GPS antenna and the appropriate RG cable and length?

Also possibly relevant items to configure noted in the Trig manual:

6.1.9.1 GPS System Certification Level
Issue AP
An important metric for ADS-B ground system behaviour is the SDA or System Design Assurance level. It is intended to reflect the probability that the GPS position source is providing erroneous information, and is based on the certification standard that was used by the GPS vendor. This will be indicated in the form of a letter code (A to D) on the data plate or installation documentation for the GPS in accordance with the standards DO-178B and DO-254, for example “DO-178B level C”. If both standards are reported but at different levels, use the lower standard (higher letter).


6.1.9.5 ADS-B Receiver Options
In the USA there are two ADS-B channels, 1090ES and UAT, and there is an ADS-B based traffic information service called TIS-B. The ADS-B ground stations relay this information between the two channels so that suitably equipped aircraft can receive traffic information. To limit channel congestion these services are only provided to aircraft equipped to receive them.
The transponder reports what receivers are installed in a periodic status message; enter the receiver status here.

6.2.5 RS232InputCheck
The RS232 interface check provides a diagnostic that the RS232 input lines are configured correctly. It will display on screen the data each RS232 line is set up to receive. If valid data of the correct type is being received, the decoded data will be shown on the display.

Post Install test:

Where installed, verification of the GPS position source and ADS-B outputs. In an aircraft with a configured GPS, pressing the FUNC button on the transponder front panel in normal operation will display the ADS position monitor. With the aircraft outside the hangar (for good GPS reception) the aircraft position should be displayed on the transponder. If the position indications are all dashes then either the GPS position is not valid or the GPS interface is not correctly configured. Whenever a valid position is received by the transponder and the transponder is in any mode other than Standby, ADS-B Extended Squitters should be observed on the transponder test set.
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Last edited by maus92 : 12-11-2016 at 12:41 AM.
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  #9  
Old 12-12-2016, 03:37 PM
jwyatt jwyatt is offline
 
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Location: Goodhue, MN
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Quote:
Originally Posted by g3xpert View Post
This is one of the protections in place to make sure there is little chance of someone spoofing the system. No radar contact, no TIS-B client services provided.
This bit of info seems important. Does this also apply to ADS-R (so my 978-only receiver can see 1090ES targets and vice-versa), or just TIS-B (sourced from radar)? I'm often dropped from radar flying at 2k' AGL away from the larger airports, it would be a shame to lose the traffic picture at the same time, only receiving same-band air-to-air targets.

With many installations taking the 1090ES-Out route thanks to solutions like the GTX 45/345/etc, Dynon, and Trig, it seems that dual-band receive is perhaps more important than was predicted a few years back, when the expectation was that the "majority of light GA will use 978 UAT." Unfortunately the few solutions that will integrate with my older EFIS are not dual-band.
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  #10  
Old 12-12-2016, 04:48 PM
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g3xpert g3xpert is offline
 
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Quote:
Originally Posted by jwyatt View Post
This bit of info seems important. Does this also apply to ADS-R (so my 978-only receiver can see 1090ES targets and vice-versa), or just TIS-B (sourced from radar)? I'm often dropped from radar flying at 2k' AGL away from the larger airports, it would be a shame to lose the traffic picture at the same time, only receiving same-band air-to-air targets.

With many installations taking the 1090ES-Out route thanks to solutions like the GTX 45/345/etc, Dynon, and Trig, it seems that dual-band receive is perhaps more important than was predicted a few years back, when the expectation was that the "majority of light GA will use 978 UAT." Unfortunately the few solutions that will integrate with my older EFIS are not dual-band.
Hello Joshua,

Yes, to quote the FAA service change document "In the FAA system, ADS-R client status is identical to TIS-B client status", so the posting above could have referred to "TIS-B/ADS-R client status" in every place it refers to TIS-B client status.

Good or bad, the U.S. is a dual frequency country with some ADS-B Out aircraft transmitting on 978 Mhz and some on 1090 Mhz, which makes it important to have a dual frequency ADS-B receiver.

The latest FAA equipage report shows that more than 70% of the aircraft which have equipped for ADS-B Out have equipped with a 1090 Mhz transmitter and there is strong evidence this trend will hold or increase.

Thanks,
Steve
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