Aerobatic aircraft should sensibly be on Mode A when operating under low level Class A/D, A35 floor, for example, to avoid triggering TCAS.
Aveling wrote:
Can anyone give the definitive word on non-Waas 430 as a position source? Some say even SIL=0 is illegal, others not. (TT21 transponder). It’s a simple cable and lots of certified GA have similar setups.Thanks
In order to know what you can wire you need to know the installation approval data.
I will take the example of the Trig TT31 in a europe registered, EASA (Annex I) aircraft.
If your transponder is installed according to the Trig EASA minor change, it’s illegal to wire it to a GNSS receiver as the wire is not documented.
Now, if the same transponder is installed in the same aircraft using CS-STAN, it’s legal provided the transponder is not DO260B compliant and SIL=0 is set. For a Trig TT31 it means that the firmware needs to be V 2.x maximum.
But this transponder might also be installed using other installation approval I don’t know of.
In an Annex II aircraft, ask your local CAA which installation data you can use (as CS-STAN and the EASA minor change are limited to EASA aircraft).
In a foreign registered aircraft, use the proper approved data. I thing Trig has a FAA STC for TT31 with SIL=3. So it’s likely legal for a SBAS enabled receiver in a N-reg aircraft.
Guillaume wrote:
In a foreign registered aircraft, use the proper approved data. I thing Trig has a FAA STC for TT31 with SIL=3. So it’s likely legal for a SBAS enabled receiver in a N-reg aircraft.
The STC required for N reg consists of a specific position source in combination with a specific transponder. So assume transponder A is paired only with position source X on an STC and transponder B is only paired with position source Y on a separate STC. Also Transponder C has an STC that permits it to be paired with either position source X or Y. X and Y are considered identical and no interface changes are required by transponder C and transponder C makes no accommodations unique to supporting either position source X and Y. So even though X and Y are interchangeable and in every known aspect identical, Y may not be paired transponder A and X may not be paired with transponder B. The only way they can be paired is with an update to the STC that allows the specific pairing. So it is meaningless to talk about an STC for the TT31 unless you also specify the specific position sources that are paired and approved on the STC.
Also, there are data elements that must be included with a position source in order for a SIL value other than 0 to be used. Most position sources simply do not provide the data necessary. It is easy to spot a broadcast attached to a position source that is not providing all the data. These broadcasts are detected by ground stations in the US as NPE (Non Performing Emitters). So even though the transponder is fully capable of being compliant with DO260B, they are detected as NPE if the position source does not have all the demanded data. In the US, aircraft owners are getting friendly letters from the FAA and client traffic services are being denied to these installations.
NCYankee wrote:
Also, there are data elements that must be included with a position source in order for a SIL value other than 0 to be used. Most position sources simply do not provide the data necessary.
What data is this?
Peter wrote:
You can’t blame them because it is a lot cheaper than spending 1000 quid on fixing an altitude encoder
Altitude encoders aren’t that expensive – I’m replacing mine to go with the new transponder, and a brand new one was £250 inc VAT (Garmin GAE12). At that price staying with my 20+ year old encoder that’s the size of a small shoebox seemed silly (plus I’m getting a little bit suspicious of the installed one)
What data is this?
Presumably the elements which are present only in the WAAS GPS data stream. But nobody is supposed to know what this is because it is under an NDA and everybody making the equipment (except Garmin) has reverse engineered it 
I find this situation really bizzare.
Peter wrote:
Presumably the elements which are present only in the WAAS GPS data stream. But nobody is supposed to know what this is because it is under an NDA and everybody making the equipment (except Garmin) has reverse engineered it I find this situation really bizzare.
ADS-B is specified in ICAO Annex 10, so how can it be under an NDA?
It’s not the ADS-B that comes out the transponder’s antenna that’s under an NDA, it’s the protocol between the position source and the transponder that’s under an NDA. There is a Garmin proprietary protocol. It’s still silly.
alioth wrote:
It’s not the ADS-B that comes out the transponder’s antenna that’s under an NDA, it’s the protocol between the position source and the transponder that’s under an NDA. There is a Garmin proprietary protocol. It’s still silly.
Both Trig and Avidyne have certified solutions for ADS-B OUT using Garmin GNS-W or GTN as the position source using Garmin’s ADS-B+ protocol. So presumably Garmin have licensed this.
Does anyone have a reference for a requirement that any working transponder must be turned on and set to its highest mode?
