I understand this for the jet world where all participants have TCAS but are not in a position to negotiate which way to turn (especially if somebody does something ambiguous / complicated to resolve, like a level bust in a holding stack – I’ve seen ATC radar videos of that and in fact then the pilots do their own actions and disperse laterally, regardless of SOP) but in a light GA proximity scenario prob99 I am the only one with the system and the other traffic is most likely non-TXP / broken TXP / broken encoder (so Mode A) / Mode C OFF / using some box which almost nobody else uses but which was evangelically plugged in a forum / etc and they most likely have no idea I am there, so it is down to me to look after myself 
The azimuth in active TAS is not accurate but is plenty accurate enough to decide which way to turn – unless the other traffic is right where you are, in which case you have possibly left it too late, but it happens sometimes if a conflict is created when turning. I’ve had a few of those, probably caused by traffic climbing up vertically under me for some time. Got one departing from Zell am See last time.
Whether this is relevant in this accident I have no idea. The SR20 might have had TAS but the UL may or may not even have carried a TXP. IF it turns out the SR20 had TAS but the UL was non-TXP, that might “draw some comments” especially from the family of the SR20 pilot whose life will have been totally pointlessly wasted for the sake of “civil liberties” for the UL pilot, but nothing will be done in the long run.
A specialist from FIS Langen, doing support for VFR flights, who posts in a German forum, says that both planes had their transponders on. FIS Langen has the radar tracks.
Peter wrote:
Airline SOPMaybe @chrisparker will have an explanation.
It isn’t an SOP, it is how the entire TCAS system is designed. All TCAS II does is tell you to climb, descend or level off and to increase or decrease the rate. There is no pilot decision making involved.
But TCAs only works if both have transponders.
I am interested Peter, why you are so sure the UL was not transponding?
why you are so sure the UL was not transponding?
I didn’t say that, I even put the word “IF” in uppercase.
It isn’t an SOP, it is how the entire TCAS system is designed
That is just a circular argument…
Actually the RA system was technology-limited when introduced many years ago.
Yes, and after many years of trying to resolve the difficulties created by the (lack of) precision in azimuth information led to the industry giving up on horizontal RAs. Given that such an up upgrade, possibly mandated by regulators, would be a huge gravy train for the avionics supplies, I suspect they did not give up lightly. Now with mode S transponders transmitting location and ADS-B, they might try again.
I am not sure there is a rational case for that, given that there are few, if any, cases of collisions after an RA was issued and followed. The only places where a horizontal RA capability would be good is near ground, where current systems do not issue any advisories below around 1,000ft above ground (radar altitude).
