General Aviation ADS-B Trial in Southern England

[Pipercubflyer]

NATS had envisaged issuing an AIC back in the autumn initiating a nationwide trial of GPS connectivity to Mode S transponders as an enabler to ADSB in/out for the GA fleet. At the request of the CAA we have not issued that open invitation to participate but have written to approximately 180 clubs and flying organisations offering the opportunity to participate in a formal trial. A sample letter is copied below;

Dear Sir/Madam,

Re: General Aviation ADS-B Trial in Southern England

As part of the development of tools to help improve flight safety by enhancing situational awareness, NATS is conducting a trial with general aviation pilots to assess the accuracy of position data from a non-certified GPS. NATS is inviting owners of suitably equipped aircraft to participate in the trial to gather sufficient data to make the study meaningful. The data can be broadcast via a Mode-S transponder with “Extended Squitter” (ES) functionality otherwise known as Automatic Dependent Surveillance- Broadcast (ADS-B).

The purpose of this trial is to assess;

a) The typical accuracy of ADS-B reported positions from non-certified GPS sources,
b) The impact of low integrity GPS data on ATC surveillance systems, and
c) The interest of GA users in ‘situational awareness’ applications that assist a pilot to visually acquire nearby traffic.

The trial will be conducted for an 8 month period from 1st January 2015 to 31st August 2015 in airspace in southern England. Further information is included in attachment 1.
Aircraft owners will need to submit a minor modification for approval to the appropriate airworthiness authority to allow the GPS to be physically connected to the aircraft’s transponder. The CAA has agreed to waive their fees for the minor modification to Annex II aircraft during the period of this trial, provided the owner registers for the trial prior to submitting the modification.
Once the modification is carried out, the participant will need to do nothing more other than fly their aircraft with the transponder and GPS turned on. Participants may be required to disconnect the GPS source at the end of the trial.

NATS will not use this data for any purpose other than the trial, such as for the provision of an ATC service. If the non-certified GPS source is used with on-board equipment that detects aircraft via ADS-B, the equipment will not be certified for collision avoidance. Pilots will continue to be responsible for maintaining an effective look out and avoiding other aircraft.

If you are willing to volunteer to modify your aircraft to connect a GPS source to your aircrafts’ transponders, please would you provide details of your:

1. Aircraft type,
2. Transponder type,
3. GPS equipment, and,
4. Aircraft engineer who will be conducting the minor modification (if known).

Participants are requested to respond to this invitation either in writing or by email to me at the address below.

Thanks in advance for your interest, and I look forward to working with you.

Adrian Price

Technical & Strategic Research
D: 01489 444827
E: [email protected]
NATS, 4000 Parkway
Whiteley
PO15 7FL


Attachment1: General Aviation ADS-B Trial in Southern England – Trial Description

The purpose of this trial is to assess;

a) The typical accuracy of ADS-B reported positions from non-certified GPS sources,
b) The impact of low integrity GPS data on ATC surveillance systems,
c) The interest of GA users in ‘situational awareness’ applications that assist a pilot to visually acquire nearby traffic.

The trial will be conducted for an 8 month period from 1st January 2015 to 31st August 2015 in airspace in southern England.
NATS low-level ADS-B coverage is centered on southern England. The diagram below is indicative of current coverage at 3500ft.An additional ADS-B receiver will supplement coverage to the north-west of this region in Spring 2015.Higher level coverage extends to most of England.

The Minimum Operational Performance Specifications for ADS-B allow the provision of position information from a non-certified GPS source, provided the Surveillance Integrity Level (SIL) parameter is set to ‘unknown’ (zero). Therefore, you may participate in this trial with a non-certified GPS source, so long as the SIL parameter in the ADS-B message is set to ‘unknown’. The positions reported via ADS-B will be compared with radar track data to establish the impact of low integrity data on surveillance tracking systems.

Not all transponders are suitable for this trial and the method for connecting the devices depends on the transponder and the GPS equipment. NATS and the CAA will work with you, your engineer and the transponder manufacturer to determine whether your aircraft and equipment are suitable for this trial and how to implement the modification. The CAA will also provide guidance for how to submit the minor modification request to EASA, see also http://www.caa.co.uk/default.aspx?catid ... ageid=9259.

Owners of EASA type aircraft will need to consult with a licensed engineer to submit an EASA form 32 to request a minor modification. Under EASA rules, it is permissible to submit one modification for multiple aircraft if they are the same aircraft type and the same equipment is used. Owners of Annex II aircraft will need to request approval of a minor modification from the CAA. The CAA has agreed to waive their fees for Annex II owners during the period of this trial.

In both cases the modification will need to demonstrate:

• The installation of the GPS equipment does not affect the safe operation of the aircraft,
• The SIL is set to zero, and,
• The GPS is not be used as the primary navigational aid
• The connection between the aircraft’s transponder and the GPS unit is non-permanent.

If the non-certified GPS source is used with equipment that detects proximate aircraft via ADS-B, the equipment will not be certified for collision avoidance. Pilots will continue to be responsible for maintaining an effective look out and avoiding other aircraft.

I have had numerous conversations with individual LAA members who are interested in participating in such a trial and I would urge those people interested to contact Adrian Price via the details above, and help us progress this exciting development.

[SteveHutt]

Note, it is my understanding that the latest TRIG and Funke Mode S transponders will automatically set SIL to '0' when ADS-B-out is enabled and fed with an NMEA data stream via RS-232 from a GPS, though this is not documented to my knowledge in the manuals. Don't know what the situation is with Garmin transponders.

Steve

[SteveHutt]

NATS are still looking for volunteers to take part in this trial. If you have the kit to allow you to participate please do get in touch with NATS on the email in the announcement and sign-up.

ADS-B is very definitely a safety enhancement and if you already have the GPS and a Mode S ES transponder then the costs are minimal.

LAA are creating a special new Minor Mod approval form especially for this, with the same local inspector check and LAA HQ sign-off so it won't be hard to do. You won't have to deal with the CAA!

Thanks,
Steve

[Sweetpea]

A big warning to all those currently with GARMIN transponders (GTX330 etc) wanting to be safer in the skies....Unless I'm mistaken, I've made life very difficult trying to get ADSB-out into my RV6 using Garmin kit .... It's a real shame safety wise, now that the LAA/CAA have deregulated ADSB-out for Permit Aircraft with uncertified GPS sources.

I originally selected the GTX330 over other transponders because traffic has always been a huge concern of mine, but I also particularly like the easy entry of squawk codes. Unfortunately I felt let down when the ADSB claims made by Garmin didn't entirely ring true without a further £960 update to Extended Squitter. Also, the pre-ADSB TIS functionality offered by the GTX330 was ever only implemented in the states and never really looked likely to migrate to Europe either.

So recently, several years on, having checked with Garmin Technical support and Harry Mendelsohn about connecting my GPSMap 496 panel mounted GPS to the GTX330 I duly forked out £960 to upgrade to the GTX330ES extended squitter version. Quick turnaround, but expensive! Let's finally get safer wrt traffic.

Now the GPSMap 496 is a WAAS enabled GPS, and therefore connecting this to the GTX330ES should provide a good source within the LAA scheme with SIL & SDA set to 0. Various sources on the net, plus Garmin and HM confirmed this. OK, it wouldn't be a certified panel mount source, but that only matters outside of the LAA ADSB scheme, right?

Nope. It seems the GTX330ES won't accept the NMEA data because the GPSMap 496 doesn't output all the WAAS data appropriately (in a "+" format). To get the right format of GPS data into the GTX330ES I've now been told I'll need to fit another GPS source (a Garmin GPS20A Waas box at a cost of nearly £700). The transponder just says "No ADSB".

Steve, anybody, can you help me with any guidance? In the meantime, I've asked HM if they can either explain themselves or get Garmin to update the software to cater for Permit ADSB installs. Given the lack of help from Garmin so far I'm not holding my breath.

Anyone else with Garmin transponders BEWARE.

[SteveHutt]

Hi Tim,

Sorry to hear about your troubles. Sadly, I can offer no comfort on the Garmin front. And I would put Bendix King in the same camp.

I have been pursuing transponder manufacturers to try to get support statements out of them for uncertified GPS Mode S ADS-B Out. So far I have succeeded with:

Trig: http://fasvig.org/trig-transponder-supp ... -ads-b-out
Funke: http://fasvig.org/funke-support-for-unc ... -ads-b-out
Air Avionics (Garrecht): http://fasvig.org/air-avionics-support- ... -ads-b-out

I have received no reply from Dittel.

Bendix King said they do not support uncertified GPS (the fact that Trig make units for BK makes this statement intruiging).

Becker do not currently support uncertified GPS but I am hopeful of a change of heart and a possible future firmware release that may change things.

I did not contact Garmin as Garmin had already notified NATS at the beginning of the trial that Garmin units would not support uncertified GPS.

The Funke statement says that older pre-v6.0 HW units do not support uncertified GPS ADS-B Out. I have been given hope that a new firmware update will be released later this year that may enable some older Funke devices not covered by the current support statement to also work. Watch this space.

As for Garmin and Bendix King, through the CAA's Conspicuity Working Group(CWG), I have been pressing upon the CAA that if they want to encourage the voluntary adoption of ADS-B in GA then the CAA needs to engage with transponder manufacturers, and especially those that are unsupportive of the uncertified GPS Mode S ADS-B Out, to ensure any and all obstacles (cost/technical/information/regulatory) to adopting ADS-B are addressed.

FYI, the final report from NATS on their uncertified GPS Mode S ADS-B Out Trial has been published to the CWG and it is very positive. Hopefully it will be released to a wider audience in the near future.

[Sweetpea]

Thanks for your prompt reply Steve, and for all your efforts more widely on this.

It's very odd that both Garmin and HM knew before the purchase that this was for a permit aircraft under the adsb trial and that I was proposing to use the 496 as the position source. Seems I've got a valid reason to go back to them given Garmin had apparently stated that they would not support uncertified GPS sources.

Besides my personal beef on this, the lack of uncertified support seems daft given the acceptance by the CAA that uncertified (correctly configured) is safer than none. Anything I can do, or the LAA membership with Dittel/Bendix/Garmin kit, can do to help you with stronger messages at the CWG?

[tnowak]

Steve,

I am still waiting to test fly my ADS-B out implementation (Trig TT21) when this awful wet wx breaks, but my GPS WAAS device only cost around GBP 50 and appears to be working okay with the Trig (on the ground). My Trig is displaying ext. GPS position data.
What exactly is your issue? Is it that your Garmin transponder won't process properly formatted data correctly from your ext. GPS or is your ext. GPS not sending data in the correct format? I think I read correctly that it is the latter?

Tony Nowak

[Sweetpea]

Hi Tony

My issues SEEMS to be that the Garmin transponder only accepts data from a certified WAAS source, rather than any WAAS source. But despite being an ex-avionics engineer,it's difficult to get to the bottom of it without some help from Garmin. Presumably, there is some way that the transponder differentiates between sources by looking at the data stream. All I know is that the advertising says "any waas gps source" which the 496 is, but this doesn't appear to be true. As Steve says, it seems Garmin do not support uncertified GPS sources, whereas Trig & Funkwerk do.

Buried in the 330es installation manual (which isn't readily available beforehand) is the statement that the gps source must supply data with a "+" format. I.e. Aviation+, NMEA+, etc. , which I presume the 496 doesn't as I can't see it in the output options. This may be a red herring, but who knows? Still waiting to be contacted by Garmin, having chased via HM. I'm really not impressed by Garmin service despite it being good quality kit. I have tested that the NMEA stream is arriving at the appropriate pin on transponder rack, so I'm sure its not electrical.....but I don't see any GPS source data on the transponder test screens.

Hopefully I can find someone who has already succesfully connected these two relatively common pieces of the ADSB-B jigsaw for some guidance.

[SteveHutt]

Tony/Tim,

There is 'Support' - the hw and sw all work together -
and there is 'Support' - the company are willing to help try to make things work -

Garmin fall foul of the latter and I believe the former.

BK are a puzzle to me. I know they fall foul of the latter, they have told me so, but I am unsure they do actually fail on the former. However, when pressed, they were unwilling to say one way or the other.

Steve

[tnowak]

Hi Tim,

I don't know anything about the Garmin equipment you are using but, assuming your transponder isn't blocking ext. non-certified GPS data, then few a few questions for you:
1.Do you know for sure if both transponder and GPS are electrically (RS-232) compatible?
2. Is your transponder set for the correct baud rate to match the output speed of your GPS?
3. Have you proved to yourself what format data your GPS is outputting? This is quite easy to do if you have a PC or laptop at home with a serial interface (and some software called PuTTY).

Tony

[SteveHutt]

Tim,

I thought this piece of information may be interesting/possibly helpful if you'd not seen it:

http://forum.pilotaware.com/index.php/t ... ml#msg3614

Steve

[Sweetpea]

Thanks for the suggestions and useful links.

Thanks Tony -
1) They're both Garmin products and I've been told that they are compatible.
2) This is an interesting one - I was told that the Garmin Txpr should auto resolve the baud rate, parity & stop bits with the Garmin GPS, but I've tried the options available (GPS TX side) to no avail. There's not a lot of config option on the Txpr side. This is where it the supporting info for GTX330ES seems pretty poor and I'm hoping to get more info during the next week via Mendelssohn Pilot Supplies. I may well need a config set that I haven't yet correctly.... but it's the lack of tech support that is making this very difficult.
3) Yep - I can see the GPS outputting the NMEA sentences by connecting it to Minicom (linux equivalent to putty) as expected and according to its various settings.

Mendelssohn Pilot Supplies have finally sensed my frustration and promise to investigate this with Garmin next week. They were under the same impression I was, in that it should work.

I'll let everyone know as soon as I hear. I'm really hoping it will work, and that it's just poor support/obfuscation that is getting in the way.

[tnowak]

I have just had my Trig TT21 ADS-B implementation "validated" by NATS.
I am using a USGlobalSat BR-355-S4 GPS receiver. My installation wasn’t quite “plug and play” but very close. I had to make up a small adapter box to house a PS2 socket for the GPS and 12V-5VDC converter module. However, only basic soldering skills needed.
If anyone wants more info please let me know.

Tony Nowak

[JohnStrong]

In the hope of saving someone the effort of trying to find out if the Garmin G3X Touch and GTX 23ES
will provide ADSB Out.

Garmin have confirmed that if the transponder "Position Integrity" (buried in the G3X Transponder Configuration pages) is set to "VFR GPS" both SDI and SDA are set to 0.

This ought to comply with the UK requirements.

We will submit our Mod application and hopefully pass the flight test.

Garmin email
"Hello John,

I’m still working on understanding CS-ACNS so I’ll have to take your word on the SIL and SDA having to be set to 0.
None the less, I verified with engineering that indeed both are set to 0 with the “VFR” selection in the G3X.

In case you are interested, you can use a GDL39 and the Garmin Pilot app to verify ADS-B parameters.
GDL 39
Garmin Pilot
I don’t think the info on how to accomplish that is on either of the product web sites, but if you’re interested after looking at the products let me know and I can follow up with the details. I know quite a few shops in the US are using this combination as a way to verify the ADS-B OUT parameters."

[SteveHutt]

Very interesting, John,
Steve