TCAS Alert logs Dec 2016 - Jul 2017


New Member
I have temporarily put online a compilation of TCAS Alert logs from December 2016 - July 2017.

My antenna has (partial) visibility to the Paris, Reims, Langen, Amsterdam and Brussels FIRs.

I use a PlaneFinder Radar Receiver in conjunction with PlanePlotter, which automatically logs Mode S Resolution Advisory (RA) downlink messages.

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Hi Frits, - great to meet you!

PlanePlotter would be nice to have running here for those TCAS alerts but, alas, no Windows hereo_O

VRS doesn't do it, but serves me well in nearly other respect.

Thanks re: Table placing. Don't worry! It's a summer thing when Gatwick (EGKK) and London airspace is ridiculously busy and it all will die down after the summer rush. I never really expected it. You're well-placed to take the top spot as things here die down here with your DX view, I suppose giving you a good amount of traffic all year round...

I don't want to hijack your thread, but couldn't miss the chance to say hello to my biggest "rival"!

73 Steve (G8IZY)
Hi Steve,

Nice to meet you too!

You probably know that there are PlanePlotter users who run it on Linux with Virtualbox:
But I don't really know how well that works. And many PlanePlotter users don't see TCAS Alert messages anyway, because they are in an area with radar stations that don't interrogate for the content of the transponder's BDS 3,0 register. For TCAS Alert downlink messages, you are dependent on these BDS 3,0 interrogations.

I found much interesting information on Mode S TCAS downlink messages and the BDS 3,0 register in this Eurocontrol Analysis of RA Downlink data :

Page 15: When TCAS triggers an RA, it uploads the BDS-30(*) register
within the Mode-S transponder. The format used for BDS-30 depends on the
capability of the associated TCAS transponder <snip>. When a ground Mode-S radar interrogates the aircraft to obtain
normal surveillance information, the transponder replies, incorporating a
flag specifying that an RA report is available. The radar then re-interrogates the transponder in order to
obtain the content of the BDS-30(*) register. This second interrogation-reply
transaction is performed during the same radar-antenna turn. The radar
station does not provide the RA downlink message as stand-alone data, but
incorporates the RA downlink message into a radar-target report with the
other surveillance data. At each radar-antenna turn, the radar beam illuminates both
aircraft involved in the encounter and the radar downlinks the content of
the BDS-30(*) register from the aircraft with RAs. When both aircraft have
RAs, the radar gets two RA downlink messages (one per aircraft) at each
antenna turn.

(*) I'm sure that the "BDS 3,0" register is meant here.

There are a lot of duplicate TCAS Alert messages in my log files and I gather from the above that there are two Mode S radars that interrogate for BDS 3,0 in my area. Two interrogations cause two identical downlink messages. I don't know yet which radar stations are doing this. One of them is likely an Eurcontrol radar.

Frits PE2G
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Hi Frits

Sorry for the delay replying, It's been a busy week!

That's an interesting pdf. It seems well written and easy to follow from the few bits I read quickly. I have saved it for reading when I get some time available to read and digest the content properly. I'm afraid that a lot of the data processing side of it will be above my head, but I'm enthusiastic about the ability to receive these messages myself (which I suppose I do anyway!) and use them. So a conceptual understanding will be good.

I think I would get coverage from some of the London radars and possibly further that ask but until I get PlanePlotter, or another program if there is one that runs natively on Linux and does TCAS alerts?, I am just assuming. I wonder if Plane Finder, itself, could decode and use these messages and display them too? It would be a good feature.

I have tried running Virtualbox before with some success, but that is not an option for me at the moment as this computer is struggling running VRS, (which uses .mono in Linux) and would collapse under the strain if I ran Virtualbox and Planeplotter as well, along with all the email, browsing etc :eek: Hopefully that problem will be solved as I have a Raspberry Pi3 sitting here for use solely as the VRS machine as it is apparently able to run VRS. That will allow me to experiment with PlanePlotter, which I have always wanted to try. That's a project for the winter though!

All the best and thanks for making me aware that this data was even present!

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