FlightAware Discussions

Overload on the use of Surveillance Radar

Interesting item from EUROCONTROL:
“Overload on the use of Surveillance Radar”

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I’m surprised it’s taken so long for them to notice this effect. When you compare message rates for stations in the US compared to Europe they usually have far fewer messages for similar numbers of aircraft. I wonder if they will implement some kind of coordination to reduce the congestion.

So am I.
Also, it’s the first time I have seen this as an explanation for the problems seen back in June 2014.
Quote from the report:
“In the worst case it could even result in the complete disappearance of the aircraft from the controller display, as already happened in central Europe in June 2014.”
News item from the time:

Eurocontrol et al has been working on this for years (decades?), it’s not a new thing.

I suppose notice was the wrong word - I’m sure they are fully aware of the limitations of the system. I hadn’t seen any official publications talking about real negative impacts of congestion other than to acknowledge that it can cause garbled messages.

The dashboard in that article is here: Communications, navigation and surveillance | EUROCONTROL

I wonder what receivers they are using - they are measuring up to 80 msgs/s per aircraft in some places. The highest I’ve seen is about 30/s per aircraft but usually only at night.

This isn’t about 1090 MHz congestion and garbled messages.
It’s about transponder capabilities, the limit of the transponder on how many long modeS messages it can send when being interrogated.

Actual frequency congestion (which also includes ModeA/C as it’s on the same frequency) is a different problem that’s not discussed in the linked article.

It’s separate issues.
This transponder limit could occur even with only 1 aircraft in the sky (and lots of radars interrogating it).

IIRC part of the limit is actually heat! - the transponders literally start overheating if required to transmit a lot of messages.

So their > 60 msgs/s or even 80 might include A/C replies and they didn’t properly label what they are talking about?

Or they are talking about burst rates over a second or something?
I’ve seen that spike up to 50 in my area.
Hmm nevermind they say the peak rates per minute … well that’s ambiguous.

@caius you should actually see one of the bad areas around Cardiff.
And from the dashboard flight paths it looks like high altitude traffic, not 100% on that though.

No matter the equipment would need to be set up to severely reduce interrogation rates for aircraft not in the airspace associated with that radar … but messing with those systems is probably not simple at all … safety critical stuff and all.

I wonder what the issue is with the transponders - it must be something like processing time because the message length even for long messages is only 112us, and 80/s is only a fraction of the available transmission time - they aren’t running out of transmission bandwidth. I would have thought it would be trivial to handle that number of messages with modern hardware, so maybe the issue is with older equipment that can’t keep up.

I can see high altitude aircraft over Cardiff. Looking at a few they have message rates around 35/s there. I’ve seen some over the channel with peaks over 40 though. It would make sense for it to mainly be high altitude aircraft because they can see more radar heads. There does seem to be some correlation - lower flying aircraft seem to have lower message rates, but I did see one at 8000 feet transmitting 30/s, so I guess location is also a big factor.

Might be interesting to gather some data and plot it.

As obj already pointed out it’s probably a duty cycle time.
Lots of tech is specified as power with a certain duty cycle.
They are 500 W transmit power, with full duty cycle that would be some seriously heavy gear :slight_smile:

I may be missing something in that case because 80 long messages a second at 1Mbps should still only be around 1% transmit time. That’s an average of only 5W, which even allowing for transmitter inefficiency shouldn’t pose any heat dissipation problems. There must be something else going on if heat is actually a problem.

Maybe the number of msgs/s are exceeding the designed heatsink size of the RF power amplifier?