Some news on ADS-B certification issues
There is good news for owners of GA aircraft on the EASA register that have a transponder, which is capable of ADS-B (extended squitter) but have not had a suitable GNSS position source.
Within the next month, EASA will be releasing an update to CS-STAN Standard Changes and Standard Repairs. If everything goes well, the update should include CS-SC005a, which will authorise aircraft maintenance engineers to connect GNSS position sources to an ADS-B capable transponder to enable ADS-B OUT.
Three configurations will be permissible under this standard change:
Configuration 1
certified transponder + certified GNSS
conforms to AMC 20-24 but with (E)TSO-C166b unit for ADS-B OUT
reports SIL = 3 and SDA = 2
Configuration 2
certified transponder + ADS-B OUT + TABS GNSS
reports SIL = 1 and SDA = 1
Configuration 3
certified transponder + ADS-B OUT + uncertified GNSS
reports SIL = 0 and SDA = 0 (for airborne traffic awareness only)
This SC is not suitable for the release to service of the aircraft by the Pilot-owner, it must be performed by a licensed aircraft maintenance engineer. However, the engineer does not have to apply for a Minor modification, which significantly reduces costs and saves time.
Please note that the CS-STAN address the airworthiness aspect (installation on the aircraft). The operation of this devices might be subject to limitations imposed by the Competent Authorities.
This is not a criticism; it is a question:
What is the motivation for EASA to get more people to radiate SIL=0 and SIL=1 ADS-B OUT?
It can be only to encourage aircraft-on-aircraft EC (electronic conspicuity). I don’t think it can be anything to do with the reasons why the FAA is going for mandatory ADS-B OUT, which AIUI is primarily for visibility to ATC. They do acknowledge “for airborne traffic awareness only” but not for the middle (SIL=1) option which can also be only good for “for airborne traffic awareness”.
bookworm wrote:
Configuration 1
certified transponder + certified GNSS
conforms to AMC 20-24 but with (E)TSO-C166b unit for ADS-B OUT
I remember having seen in a draft of the new Standard Change that this was allowed only if the transponder manufacturer had stated that the particular GNSS unit was compatible with the transponder for ADS-B out purposes. Has this restriction been removed in the final version?
TABS GNSS
What’s that?
Airborne_Again wrote:
I remember having seen in a draft of the new Standard Change that this was allowed only if the transponder manufacturer had stated that the particular GNSS unit was compatible with the transponder for ADS-B out purposes. Has this restriction been removed in the final version?
It will still be necessary for the transponder manufacturer to indicate compatibility of the transponder with the GPS position source or protocol (for example as Trig does in section 5.6.9 of its TT21/22 IM).
TABS GNSS is a position source qualified to TSO-C199 class B.
Airborne_Again wrote:
I remember having seen in a draft of the new Standard Change that this was allowed only if the transponder manufacturer had stated that the particular GNSS unit was compatible with the transponder for ADS-B out purposes. Has this restriction been removed in the final version?
If this part remains, it will be open to interpretation. A lot of transponder installation manual pre-date CS-STAN (or don’t care). So we will never have a section saying “For the purpose of CS-SC005a, the following GNSS source are acceptable”
So the pragmatics would take sentences like " Position feed can be NMEA , «Aviation» protocol, …" to be good enough. Gold-platers will look to see if SchenzenGPSUltimate is explicitly listed.
The installation manuals for US-made transponders (which is most of those in use in Europe) make no concession to any European regs, from what I have seen.
Xtophe wrote:
If this part remains, it will be open to interpretation. A lot of transponder installation manual pre-date CS-STAN (or don’t care). So we will never have a section saying “For the purpose of CS-SC005a, the following GNSS source are acceptable”
But it doesn’t have to explicitly refer to CS-SC005a. E.g. The Trig TT31 IM says: “The TT31 transponder can be connected to the following GPS units to form the basis of a CS-ACNS compliant ADS-B installation: Trig TN70, FreeFlight 1201, Accor NexNav Mini, Garmin GNS4x0W, Garmin GNS 5×0W, Garmin GTN series.”
bookworm wrote:
TABS GNSS is a position source qualified to TSO-C199 class B.
What’s the difference compared to a “normal” panel mount IFR-approved GPS?
Airborne_Again wrote:
What’s the difference compared
Looking at what Trig offers for pure GNSS sources (no navigation, radio, …) (TN70 vs TN72), there is a ~ £1000 difference
You remind me of the joke about the old Scottish woman (you did mention Trig!) who opens the door to find the local dispensing chemist looking worried.
“Oh Mrs Munroe, I’ve made a terrible mistake. Earlier today, instead of giving your husband a vial of morphine, I gave him a vial of strychnine.”
“Morphine, strychnine”, says Mrs Munroe, “what’s the difference?”
“Two shillings and sixpence please” says the chemist.
The TABS TSO-C199 was designed to be a standard for a low cost electronic conspicuity device that supports both ADS-B and visibility to TCAS. But it’s lower power than a transponder and doesn’t respond to ground interrogations, to keep the cost and power consumption down. In addition, to keep the cost down compared to a fully certified WAAS chipset, the use of a commercial GPS chipset is allowed for the position source, provided the chipset passes certain tests. The radio functionality is covered under TSO-C199 class A, the position source as TSO-C199 class B.
TABS class A has had limited take-up, as I think manufacturers found that it didn’t offer much saving compared to a normal TSO-C166 transponder. But the idea of taking £1000 off the cost of the position source for ADS-B has proven much more popular, hence when you hear or read TABS these days, it’s usually referring to a TSO-C199 class B position source, even though the acronym is “Traffic Awareness Beacon System”.
