Dan

The reason to ignore ADS-B traffic data from non-conforming aircraft is because thats what the standards say to do. I think this comes in via TSO-C195 and the RTCA standards it incorproates but I'm not going to spend time chasing this down now.

And if you are an RTCA committee member focused on airlines and government regulators and and avionics manufactures... and care about critical IFR spacing, ground surface spacing, etc. and know that COTS GPS errors can be way more than a few hundred feet at times... then surely you would argue that is reasonable. And from their view surely nobody is going to want to fly around transmitting ADS-B Out using a crappy COTS GPS that don't have trusted reliability ( e.g. like RAIM).

The eventual come back on this was.... the development of TSO-C199/TABS which is a middle ground that leverages COTS type technology internally. Unfortunately the FAA never closed the loop to allow TSO-C199 GPS sources for ADS-B Out in certified gliders.

I also don't want to think lots of aircraft could have random COTS GOPS connected to an ADS-B Out and be flying around close to dense traffic areas. It's all frustrating as well since all this is inherently insecure, with no encryption or authentication and bad actors could already do a lot of harm injecting fake traffic into the ADS-B system. This non-compliant ADS-B traffic display hurdle does nothing to stop that. Why the designers of ADS-B did not implement authentication, encryption and some form of useful security is beyond me. Oh well we need to keep the NAS primary radar systems around anyhow.... for when all this goes tits up.

It might be time to get used to what the airlines and high-end users want. With FAA privatization there may be much more of that....


On Friday, September 22, 2017 at 9:07:06 AM UTC-7, Dan Marotta wrote:
Jumping into the middle of this - what's the real reason to ignore an
ADS-B Out aircraft simply because the GPS source is "crappy"?Â* So what
if the position is off by 100 feet or so?Â* My PowerFLARM routinely
reports targets at 200 feet or more altitude difference, e.g., I may get
a report of a target 100 feet high and spot him a hundred feet or so
lower than I am.

It just seems ridiculous to ignore another aircraft which might be on a
collision course simply because his altitude or position may be reported
as a couple of hundred feet different from where he is. That's what
looking outside is for.Â* Following the same logic, of what use is a
non-TSO compliant GPS in an experimental aircraft if it will be ignored
by other aircraft?

Inquiring minds and all...Â* BTW, I plan on installing a TN70 to mate
with my TT22 in my certificated glider.

On 9/21/2017 7:41 PM, Darryl Ramm wrote:
On Thursday, September 21, 2017 at 6:20:54 PM UTC-7, wrote:
What hasn't been discussed is how often non-approved ADSB out sources are actually being ignored.
Ah I think we've been over what matters here many times, but it is a mess.

100% of certified ADS-B in systems will ignore the ADS-B data from 100% of ADS-B Out systems that use a COTS/non-complaint GPS source 100% of the time.

So airliners, fast jets, regional jets, etc. which if they have ADS-B In at all will be a certified In system, definitely won't see some scabby ADS-B Out install using a COTS GPS source. Since many of those aircraft today have TCAS II they will be see the transponder via TCAS and be able to issue TCAS TA and RA fro that target. However the gap in the middle is with many high-end GA aircraft that have certified ADS-B In but no TCAS, they won't see a crappy COTS driven ADS-B Out. But at the low-end GA market non-certified portable ADS-B In systems will see those COTS powered targets. That is kinda brain dead but it's how it is and easy to work around.. don't use a COTS GPS source....

With the relatively low price of theTN72, if owners want to equip an experimental glider with ADS-B Out there is no excuse anymore for using a COTS GPS source. I really don't want to get into how many GA aircraft might or might not be affected, just do it properly and install a TN72 or TN70 system. COTS GPS is just the wrong thing.


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Dan, 5J