Verifying Mode S ES ADS-B Out transponder setup - Can PilotAware help?

[SteveHutt]

Hi Lee,

You will be aware of the growing number of pilots looking to setup their aircraft to broadcast ADS-B Out from a Mode S ES transponder which is being fed with a position source from an uncertified GPS. Indeed, you have recently enabled NMEA0183 GPS position data feed out of PilotAware to facilitate this.

The current LAA approval process for ADS-B Out with an uncertified GPS position source is described below. This process is inconvenient for those living outside the Southern England NATS ADS-B ground receiver coverage area. I am therefore wondering whether PilotAware may be able to help?

The requirement of the LAA approval process is to verify that various settings in the ADS-B Out message are set correctly. E.g. SIL=0 and SDA=0. These settings will be in the ADS-B messages that PilotAware is already reading but for which PilotAware currently has no use.

Would it be possible in some fashion for PilotAware to make these setting values visible? It is not something that is needed ordinarily for traffic situational awareness while flying but could be helpful on the ground for checking/diagnosing ADS-B Out configurations. I wondered whether a slightly tweaked alternative version of PilotAware (i.e. not for use while flying, but in a different programme download) could capture and write a formatted log on the SD card. Subject to agreement by the LAA, pilots could generate a log showing their ADS-B message format and send off a copy to the LAA to prove their ADS-B configuration is correct. This would remove the reliance on NATS for setup verification.

I know there is existing sophisticated certified Avionics kit that can do this, but they are rather expensive. I am interested in a much more cost effective solution.

I would be grateful for your thoughts on this matter?

CURRENT LAA UNCERTIFIED GPS ADS-B OUT APPROVAL PROCESS
For LAA Permit to Fly aircraft, the current procedure to verify the setup (i.e. that the transponder is broadcasting the correct data) is detailed in the LAA TL3.03 and MOD 7 & MOD 14 documentation. Part of this requires getting an email from NATS confirming the data they received from the ADS-B Out broadcast was correct. This was the closest available mechanism equivalent to that used to verify new standard transponder setups via an RT exchange with a Radar Controller while flying in their area. To enable NATS to see your ADS-B broadcast means having to go flying within the coverage area of the NATS ADS-B ground receivers, which does not cover the whole of the UK.

Regards,
Steve Hutt
FASVIG Programme Coordinator

[scsirob]

Just a thought..

In PAW you already input your 24-bit ICAO code. So when PAW receives ADS-B, it will see its own ICAO code. Perhaps adding one or two lines to the web interface showing "This station: <flag A><flag B><flag C>", whichever flags need to be set correctly, and then making a screenshot to send to the LAA will allow you to self-certify?

[Moffrestorer]

Hi Steve,

I'm at a loss to know how to make the required setting for SIL and SDA. There is no mention in the installation and operation manual for the Becker BXP6401-2 transponder which we have in our EV97A.

I emailed Harry Mendlessohn technical dept. where we purchased it and they haven't been able to elicit any info from Becker. HM weren't aware any settings needed to be changed on these units.

Some different makes seem to apply these settings automatically, perhaps the same for Becker. Do you have any information on how to achieve these settings, or do you know of anyone who can help?

Sorry for misusing PAW forum in this way but didn't know how to contact you otherwise. Any reply you give might in any case, assist other PAW users.

[SteveHutt]

Just a thought..

In PAW you already input your 24-bit ICAO code. So when PAW receives ADS-B, it will see its own ICAO code. Perhaps adding one or two lines to the web interface showing "This station: <flag A><flag B><flag C>", whichever flags need to be set correctly, and then making a screenshot to send to the LAA will allow you to self-certify?

Hi Rob,
Possibly. To be honest I don't really want to define the solution, just the requirement.
I'd be happy with any way that achieves visibility of the required data that can be done in a way that would be acceptable to the LAA.
Thanks,
Steve

[SteveHutt]

Hi Steve,

I'm at a loss to know how to make the required setting for SIL and SDA. There is no mention in the installation and operation manual for the Becker BXP6401-2 transponder which we have in our EV97A.

I emailed Harry Mendlessohn technical dept. where we purchased it and they haven't been able to elicit any info from Becker. HM weren't aware any settings needed to be changed on these units.

Some different makes seem to apply these settings automatically, perhaps the same for Becker. Do you have any information on how to achieve these settings, or do you know of anyone who can help?

Sorry for misusing PAW forum in this way but didn't know how to contact you otherwise. Any reply you give might in any case, assist other PAW users.

Hi Moffrestorer,
You are correct. The Trig, Funke and Garrecht Mode S ES transponders set SIL/SDA/etc correctly for an uncertified GPS if fed with NMEA0183 data.
I am afraid I don't know about the Becker transponders. I would suggest contacting Becker directly yourself.

I did do a bit of googling and found this:
http://www.becker-avionics.com/download/Manuals%20and%20Specifications/BXP%206400_Family/BXP6401-X-(XX)%20Installation%20and%20Operation%20Issue3-ads-b.pdf

Don't know if you have read that doc but it does seem promising. In particular it says:

B. The equipment is capable to operate with following certified GPS receivers:
- FreeFlight System GPS/WAAS 1201 Sensor, part number 84100-02-XXXX
- NexNav miniGNSS/ GPS-SBAS Sensor/ Receiver.
The equipment is capable to operate with following non-certified GPS receivers:
- Garmin GNS 430
- Garmin GNS 530
The equipment is also capable to operate with GPS receivers which provide
EIA-232C or EIA-422 interface with serial asynchronous transmission parameters:
4800, n, 8, 1 and transmit data with NMEA-0183 protocol GGA and VTG
sentences.

The fact that it is even discussing "non-certified" GPS and NMEA I would take as very hopeful.
If your setup menu allows you to specify the type of connected GPS then there is a strong probability that is what dictates the SIL/SDA settings.
With an ADS-B diagnostic capability such as that which I posted about in the first post on this thread you would be able to see what effect the settings had.
Without that you will need to get confirmation from Becker I think.

I hope that helps. Do let me know how you get on. I suspect you will find it can be made to work.
However, I would also check the firmware levels (latest vs. the one in your transponder).
These sort of things (control over settings) can change from one firmware version to the next.
I am currently seeking confirmation on required firmware for uncert ADS-B Out with Trig.

Regards,
Steve

[SteveHutt]

Also found this, which might some may find helpful:
https://www.gliderpilotshop.com/adsb5
Steve

[Admin]

Hi Steve,

I will investigate whether this can be done, on the face of it, it sounds trivial, but with most things - the Devil is always in the detail

Thx
Lee

[Richard]

I'm Currently setting up with NATS for the ADS-B Trials..... I can only speak as a Trig User.  The SIL=0 and SDA=0 Levels are, I think, the levels that the NATS flight recording sees the aircraft. Level 6 been the highest ( Certified Traffic & GPS)

For Trigg you need the latest version update. Then set the transponder to "Uncertified GPS Source"  There is no setting within the GPS Source to set the SIL=0 and SDA=0 levels this is within the Transponder. The GPS just supplies the relevant GPS info.

This Is how I understand it but if I'm incorrect I apologize and wait to be corrected.

[SteveHutt]

Hi Lee,

Thanks very much. Yes, I would think that decoding the ADS-B message would indeed be trivial. It is the question of how best to/whether to integrate this functionality into your 'system' or to create a separate download that is the trickier bit. I will leave that to you.

Bottom line is that this 'ADS-B Message Analyser' is a really important and useful capability. It just needs to be implemented in a user-friendly manner and delivered such that the functionality can be relied upon on an ongoing/permanent basis (e.g. future support for any required updates) such that the output data format could potentially be built into an LAA ADS-B Out approval process.

Steve
(who many years ago used to be an IBM mainframe systems programmer/assembly language programmer so well understands programming concepts just haven't kept up to date with the likes of programming the RPi  )

[SteveHutt]

I'm Currently setting up with NATS for the ADS-B Trials..... I can only speak as a Trig User.  The SIL=0 and SDA=0 Levels are, I think, the levels that the NATS flight recording sees the aircraft. Level 6 been the highest ( Certified Traffic & GPS)

For Trigg you need the latest version update. Then set the transponder to "Uncertified GPS Source"  There is no setting within the GPS Source to set the SIL=0 and SDA=0 levels this is within the Transponder. The GPS just supplies the relevant GPS info.

This Is how I understand it but if I'm incorrect I apologize and wait to be corrected.

Hi Richard,
I'm guessing you were the Richard who was bcc'd on the email I received from NATS last week related to Trig firmware. I'm just getting Trig to confirm the minimum software version required to support ADS-B Out with uncert GPS to avoid bad advice that would cause people to send in their transponders for unnecessary upgrade. It's taking Trig a little while to make the checks to make absolutely sure. And yes, with the correct firmware the Trig TT21/TT22/TT31 transponders will set the SIL/SDA/etc values correctly for uncertified GPS if fed with NMEA 0183 format GPS data.

Re: SIL/SDA/etc and ADS-B message specs, this is a useful reference (so long as you ignore the U.S. only info, e.g. regarding UAT):
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2020-165.pdf

SIL = Source Integrity Level (basically SIL=0 means "Unknown")
SDA=System Design Assurance (again, 0 means "Unknown")

Thanks & Regards,
Steve

[scsirob]

Re: SIL/SDA/etc and ADS-B message specs, this is a useful reference (so long as you ignore the U.S. only info, e.g. regarding UAT):
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2020-165.pdf

SIL = Source Integrity Level (basically SIL=0 means "Unknown")
SDA=System Design Assurance (again, 0 means "Unknown")

Thanks & Regards,
Steve

Reading this document, it appears that SDA is a hard-coded firmware value that the transponder manufacturer has to set. SIL is something that should be set at installation. A fully certified solution can have a SIL>0. Neither seem to be a function of the GPS data source.

I assume the LAA test wants to verify that simple installations with non-certified GPS sources do not confuse any transponders into transmitting bogus information. It would be kinda bad if a flawed ADS-B transmission inadvertantly projects you in the path of an airliner. Having SIL and SDA at zero will flag your information as unreliable or even 'to be ignored' for daily operations.

For PAW this probably means that sending $GPRMC strings over a serial port is the only thing that's required for this to work. It's up to the transponder firmware to handle things properly after that.

[SteveHutt]

Hi Rob,

Neither seem to be a function of the GPS data source.

Setting SIL is not a function 'performed' by the GPS device but it is a function 'of', as in 'should be dependent on' the GPS device.

SIL is based solely on the position source’s probability of exceeding the reported integrity value and should be set based on design data from the position source equipment manufacturer.

It wouldn't generally be applicable to the type of a/c we are talking about, but AC 20-165 describes far more sophisticated scenarios such as dynamically selecting GPS data feeds from one of many installed GPS devices where the SIL setting might need to be dynamically changed based on the GPS data source selected at any given time.

I assume the LAA test wants to verify that simple installations with non-certified GPS sources do not confuse any transponders into transmitting bogus information. It would be kinda bad if a flawed ADS-B transmission inadvertantly projects you in the path of an airliner. Having SIL and SDA at zero will flag your information as unreliable or even 'to be ignored' for daily operations.

For PAW this probably means that sending $GPRMC strings over a serial port is the only thing that's required for this to work. It's up to the transponder firmware to handle things properly after that.

Yes, correct, plus the installer ensuring the right settings are configured in the transponder's setup menu.
Current regs stipulate that airliner TCAS systems should ignore ADS-B messages with SIL=0.

Steve

[Richard]

I'm Currently setting up with NATS for the ADS-B Trials..... I can only speak as a Trig User.  The SIL=0 and SDA=0 Levels are, I think, the levels that the NATS flight recording sees the aircraft. Level 6 been the highest ( Certified Traffic & GPS)

For Trigg you need the latest version update. Then set the transponder to "Uncertified GPS Source"  There is no setting within the GPS Source to set the SIL=0 and SDA=0 levels this is within the Transponder. The GPS just supplies the relevant GPS info.

This Is how I understand it but if I'm incorrect I apologize and wait to be corrected.

Hi Richard,
I'm guessing you were the Richard who was bcc'd on the email I received from NATS last week related to Trig firmware. I'm just getting Trig to confirm the minimum software version required to support ADS-B Out with uncert GPS to avoid bad advice that would cause people to send in their transponders for unnecessary upgrade. It's taking Trig a little while to make the checks to make absolutely sure. And yes, with the correct firmware the Trig TT21/TT22/TT31 transponders will set the SIL/SDA/etc values correctly for uncertified GPS if fed with NMEA 0183 format GPS data.

Re: SIL/SDA/etc and ADS-B message specs, this is a useful reference (so long as you ignore the U.S. only info, e.g. regarding UAT):
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC%2020-165.pdf

SIL = Source Integrity Level (basically SIL=0 means "Unknown")
SDA=System Design Assurance (again, 0 means "Unknown")

Thanks & Regards,
Steve

Steve,
   Thank you for your reply above.  I'm not sure the NATS Email was referring to my self or not, I have been chatting with NATS via email for a little time now, trying to get it right first time.

OK... the conclusion so far is my TT21 was in need of an update. The firmware that was installed was 1.4 in the unit. This version only allowed me to set the SIL option to "Low" (VFR or uncertified) which with the confirmation of my LAA Inspector was what was required. But sadly this is not the case. It reported on the NATS System as Level 6 which is the same as the big boys/Girls transmit.

Now contacting Trig in Scotland by phone, a good chat with support, came to the conclusion the TT21 was in need of a firmware update. who very promptly returned the unit in just 3 days. It is now running version 2.7 which allows the control head to displays the GPS reference so you know it is working.

GPS Certification......  Uncertified
GPS NAC Velocity......  Unknown

I already have a GPS source in the aircraft but using setting NMEA from the PilotAwre would now work perfectly.

I still need to do the test flight again to get confirmation. I hope this helps in your quest to find the minimum firmware required for the NATS Trials but to confirm that Ver 1.4 is no good

[Welsh Pilot]

I have been talking to Becker regarding my BXP6401-2.

As mine is pre serial number 1999 I require a Firmware upgrade to Ver 2 and a hardware modification Ver 3.

I have queried the SIL SDA settings and this is their reply:

"I have checked and in our ADS-B solution in BXP6401:
-           the Surveillance Integrity Level is set to “0”
-          the System Design Assurance is set to „2” (it corresponds to Software & Hardware Design Assurance Level C)"

It would appear, but I am going to ask for clarification, that even after the upgrade the BXP6401 is still unsuitable for the NATS/CAA trial.

I will post when I have more information.
I have also attached the service bulletin.

[Moffrestorer]

Welsh Pilot,

Hmmm, I attempted to contact Becker yesterday in this regard. So far Becker haven't answered my queries directed through Harry Mendlessohn's dealership. From the reply you received as looks as though the SDA setting will be the fly in the ointment.

Do you know whether it is a user setting that can be altered or is it set by Becker in the firmware? There appears to be 6 levels of SDA setting (from what has been said in this forum) and I guess NATS would find a SDA=2 to be unacceptable. I'm presuming it's nothing to do with the quality of the transponder, but a function of the GPS that we want to connect to it.

This ADSB lark, and the way the manufacturers have implemented it all seems to be a bit of a pig's breakfast, considering they happily sell their transponder's to the GA user.

I'm very interested in what else you are able to find out.

Chris