Reducing the cost of ADS-B - Today's announcements

[SteveHutt]

Please see here:

http://fasvig.org/reducing-the-cost-of-ads-b

Many thanks to Lee and the PAW team, in response to my request, delivering the PAW Traffic Display which will now be used as the ADS-B configuration verification mechanism in the BMAA and LAA Non-certified GPS Mode S ES ADS-B avionics MOD approval process.

The above link also provides access to the report by NATS on the GA ADS-B trial that was conducted in 2015.

Steve

FASVIG Programme Coordinator

[flying_john]

Reading through the trial report it all looks very good, but it did raise a question in my mind about the source of the altitude data sent  Ext Squit.

Is it derived from the Txpdrs own altitude used in the normal Mode C transpond or does the PAW send an altitude as part of the NMEA sentences sent out of the serial port.

If it is the Paw altitude that is used in the ES message and you dont have the barometer board fitted, presumeably it uses the GPS altitude.

It was also noteworthy that none of the trial airframes  used Null SIL and SDA values even though there are Controlled Air Traffic still not using SIL and SDA. Does this preclude some Mode S transponder users from ever taking part in ES.

John

[SteveHutt]

John,
I'm pretty sure the transponder is going to use it's own altitude, not that from the GPS. It ought to be consistent with the non-ES data.

Re: Null SIL/SDA,
SIL and SDA have been specified as being required to indicate the status of the GPS position source. As such it therefore mandates that the transponder must support ADS-B v2. Earlier versions do not support both SIL and SDA.

Steve

[flying_john]

SIL and SDA have been specified as being required to indicate the status of the GPS position source. As such it therefore mandates that the transponder must support ADS-B v2. Earlier versions do not support both SIL and SDA.

That being the case why are there instances of Big jet traffic not send SIL and SDA. Do they have some sort of dispensation one wonders.

If the Txpdr uses its own derived altitude (in the case of Funke it is an on-board barometric capsule)  why does the altitude get sent out of the USB port.  Is there anyone who is "au fait" with the ADSB-ES spec who could verify where the ES messages are supposed to derive their altitude from.

John

[SteveHutt]

John,

See here: http://www.icao.int/APAC/Meetings/2015%20ADSBSITF14/IP11_USA%20AI.4%20-%20Differences%20in%20ADS-B%20requirements_final.pdf

This confirms altitude is based on barometric pressure in Table 1.

Re: Dispensations
EASA ADS-B mandate applies to:
Fixed wing a/c >5700 kg or >250kts TAS
For new aircraft registered after 8 Jan 2015
Retrofit to older aircraft by 7 Dec 2017

So, right now ADS-B is not yet mandatory in Europe at all for CAT aircraft registered before Jan 2015.
Many of these may well have older V0 or V1 standard ADS-B.
V0 does not output SIL or SDA.
V1 does not output SDA but does output SIL, but a SIL with a slightly different definition to SIL in V2.

Note that the EASA mandate for ANSPs (ATC) to use ADS-B is Jan 2020.

See here: http://www.icao.int/APAC/Meetings/2010/adsb/sp22.pdf

Steve

[flying_john]

Thats a useful reference. Thankyou

It does still raise the question, why is SIL = Null and SDA = Null  is not treated the same as SIL = 0 and SDA = 0. This would make both older commercial traffic and older GA ADSB useable with no modification.

It is interesting to see that in the table on P3 of the document it says that SIL and SDA are "Required" with values of >= 2 and >=3 in Europe.

I think the early adopters of Mode S,  whilst being able to Squitter, are now being penalised because their Txpdrs do not assign the SIL and SDA field without an expensive upgrade.

What pressure can be bought on Funke to modify their early products to be compatible with the requirements, I wonder.

John

[SteveHutt]

John,

Re: Funke,
I forget right now the precise hardware definitions but Funke transponders fall into three categories:

1) units with hardware AND firmware that can do SIL=SDA=0 ADS-B Out now
2) units with hardware that could do SIL=SDA=0 ADS-B Out but firmware that does not support it
3) units with hardware that could never do ADS-B Out

So, category 1) is done. If you have one of these unit with the wrong firmware there is a firmware upgrade path. Category 3) units are out of luck. For category 2) units, Funke advised me that they plan to release a new firmware version in 2016Q2 that would enable SIL=SDA=0 ADS-B Out.

Steve

[SteveHutt]

The new LAA MOD 7 and MOD 14 forms that detail the ADS-B Out verification using PilotAware have been published.

See: http://www.lightaircraftassociation.co.uk/engineering/StandardForms/LAA-MOD%207%20-%20Avionics%20Installation.pdf
and: http://www.lightaircraftassociation.co.uk/engineering/StandardForms/LAA-MOD-14%20-%20ADS-B.pdf

LAA MOD 7 is for a full avionics approval. LAA MOD 14 is for adding ADS-B Out with a non-certified GPS onto an already approved Mode S ES transponder.

Just need the BMAA docs now.

Thanks again to Lee and the PilotAware Team for making this possible.

Steve

[flying_john]

Re: Funke,
 Funke transponders fall into three categories:

1) units with hardware AND firmware that can do SIL=SDA=0 ADS-B Out now
2) units with hardware that could do SIL=SDA=0 ADS-B Out but firmware that does not support it
3) units with hardware that could never do ADS-B Out

Yes they do.
 The Cat 3 is because they did not make the harness with the Data input wire - but its a simple upgrade, then change to V 5.3
 The Cat 2 does not set SIL and SDA  Version 4.7 MOD 10 status - it is a null field. Funke want £250 to upgrade to Cat 1 and have offered it to me, but it is a cost too far as my expectation, as an early adopter of their product and who has been subject to a recall previously, is that they conform to the full spec at their expense.

In my view this is poor customer service and whereas I was considering their 8.33 product, I will now look at alternatives.

[Andy Fell]

I'm with you, John.  Asking for £250 for a SW upgrade which fixes something that is supposed to work is a bit of a cheek!

I was the one on the NATS trial who had the TT21 with old software in (early adopter!), so I had no way of setting SDA/SIL to 0.  NATS picked this up and were ok for the period of the trial, but I since sent my TT21 back to Trig; they updated the software and posted it back to me FOC.