Peter wrote:
The % of GA emitting SIL=3 is really small. It is basically higher end IFR types which have an ADS-B OUT capable Mode S transponder (in Europe it is not possible to emit certified ADS-B OUT without Mode S) fed from an SBAS (WAAS/EGNOS) GPS.
I’d say most mode S transponders are capable of ADS-B out. Even the most basic Trig TT21 can do that. It is more critical that you have an SBAS GPS source — and of course that everything is wired correctly. But that’s something you find not only in high end IFR aircraft.
Some recent US statistics as of 4-1-2023. GA aircraft 205,000 of all types. Equipped with compliant ADS-B Out systems: 163,000. About 3/4 are 1090ES and the rest are UAT. Of these, In the GA fixed wing fleet, about 110,000 aircraft are equipped, but a little over 5000 are NPE (Non Performing Emitter) which means they have issues and can’t be used. Portable ADS-B Out is virtually non existent and not allowed, so the NPE aircraft have either bad installations or inputs such as pressure altitude or GPS source is not compliant. I had a failure of a missing pressure altitude in my UAT ADS-B Out system making me NPE. TRACON (Approach and departure control) didn’t notice because they were getting the altitude from my mode S transponder, but ARTCC (Center) did notice the issue as they seemed to be using a Fused (all inputs from secondary radar, primary radar, ADS-B Out, multilateration). TRACON and ARTCC use different computer systems. My issue was resolved by changing the source for the pressure altitude to the UAT system.
With about a quarter of GA aircraft not being equipped and about 10% without a transponder with mode C, the ground station TIS-B product can fill in providing traffic information for most (60%) of the remaining targets in the enroute phase of flight, but not in the traffic pattern where many of the mid-air’s occur. TCAS or TAS can fill in for these in the traffic pattern and anywhere outside a TIS-B SV which requires being inside both a secondary radar SV as well as a ADS-B ground station SV. Also TCAS and TAS don’t require the target to have a working mode C, just mode A, to provide target information.
Not all certified traffic display systems provide target information on the ground, example a GNS430W/530W coupled with a GTX-345. The GTN 650/750 systems coupled with a GTX-345 or GDL88 will show ground traffic of ADS-B Out targets. Although portable systems will show anything they receive, including NPE targets. I am not a fan of portable systems for providing traffic information as they are not required to use the more sophisticated traffic alerting algorithms and often have antenna issues because of metal airframes and therefore can miss the one and only ground station assigned to generate their TIS-B. While FIS-B is highly redundant and missing one ground station will usually not impair receiving weather data, that is not the case with TIS-B.
ADS-B In is not mandated in the US anywhere and is only approved as an aid for visual acquisition of traffic. This is from the AIM 4−5−7. Automatic Dependent Surveillance−Broadcast (ADS−B) Services:
e. ADS−B Limitations.
The ADS−B cockpit display of traffic is NOT intended to be used as a collision avoidance system and does not relieve the pilot’s responsibility to “see and avoid” other aircraft. (See Paragraph 5−5−8, See and Avoid). ADS−B must not be used for avoidance maneuvers during IMC or other times when there is no visual contact with the intruder aircraft. ADS−B is intended only to assist in visual acquisition of other aircraft. No avoidance maneuvers are provided or authorized, as a direct result of an ADS−B target being displayed in the cockpit.
Legalese words that I think result from the delay (and associated position inaccuracy) associated with traffic data received from an ADS-B ground station, versus directly from the plane. Also because FAA doesn’t want IFR traffic darting all over the place without ATC direction or control, using ADS-B traffic data as justification.
Otherwise it’s fairly obvious that the use of ADS-B IN is quite useful ‘assistance’ to see-and-avoid, especially when you never actually see the other planes. In my VFR usage I’d estimate that as being over half the time but you can bet that I adjust my track to minimize conflict anyway, without any need for authorization if I’m not talking to ATC.
I find that it does help with traffic awareness and the ability to locate traffic visually, although I don’t expect to see other GA aircraft visually until they are within 2 NM. I like the Garmin relative traffic trend presentation on my GTN750Xi and G500TXi as I find it very helpful to determine if the nearby traffic is a threat or going to possibly be in the future.
