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-   -   Air Traffic Control out in Sweden (https://www.pprune.org/atc-issues/570294-air-traffic-control-out-sweden.html)

Klauss 7th Nov 2015 17:41

Air Traffic Control out in Sweden
Hi, I read newspaper articles that there was an outage of air traffic control in Sweden on the 4th of November. Anyone have Details ? What didnīt work anymore ?
Thanks .

Una Due Tfc 7th Nov 2015 18:51

Procedural isn't taught in many places anymore, and how comfortable would you be sitting down with paper and a pencil and doing it for the first time in a few decades with live traffic?
I certainly wouldn't be.

G0ULI 7th Nov 2015 18:55

There are no procedures except land as soon as possible.
If the geomagnetic disturbance from the flare is severe enough, radio doesn't work, radar doesn't work, and GPS signals are lost. Radio based navigational aids will also fail or be unreliable.

So strict VFR flying conditions with no external contact between aircraft and the ground or other aircraft and no navigational information except eyeballs and paper charts. Even that may not work if compasses are inaccurate, as they often are that far north in geomagnetic storm conditions.

Still want to fly?

Sometimes we just have to recognise that nature is bigger than our technological solutions.

kcockayne 7th Nov 2015 19:44

Procedural really ought to be taught & be available. However, keeping proficient enough to be able to use it I in a serious situation with lots of traffic is problematical. it was abandoned partly because of the reliability of Radar systems, but also as a cost saving matter. I think that the cost saving element was given far too high a priority & that Procedural training should have continued.
I also have to reflect that when undergoing TRUCE training, ATCOS at my unit, who had no experience of controlling without SSR, were at a complete loss of how to continue Radar Control using PRI only. This is highly regrettable & ought not to be allowed. But, that is the modern way, & every penny counts !

055166k 7th Nov 2015 20:15

You may find that London Control is not authorised to provide a non-radar service except for short term clear the sky purposes.

kcockayne 7th Nov 2015 23:17

I have to admit that it is very hard to imagine any effective sort of Procedural Control taking place in the very busy, & complicated , airspace that we have now. But, it would be a useful tool for ATC to use to provide some sort of service when Radar is u/s. Although, it should be possible to provide back-up Radar within a short while of a failure in the service.
Let's face it, if the Radar fails in busy airspace, it is an emergency situation which can only be resolved effectively by the use of a replacement Radar service. But, I continue to feel that Procedural experience & ability could help in the provision of a safe contingency ATC service, both in the immediate aftermath of the Radar failure & in the longer term, before the Radar is restored.

Klauss 8th Nov 2015 05:16

hmmm....so, Radar didnīt work, and the newspaper didnīt mention GPS. I guess that worked fine, then. Were any notams out ?
Procedural control must be quite difficult with many planes in the sky.... I think Iīd like to stay out of and area where this is done, if I had a choice.

NiclasB 8th Nov 2015 10:09

A friend of mine who works at Sweden Control (but was not at work during the incident) tells me that the MSSR system (1030/1090 MHz) was compromised such that the same aircraft could be displayed up to 10 times along a 20-30 mile track. The disturbance was "medium", which is ironic; if the disturbance had been stronger, the system would have filtered out the bad echoes by itself. The "medium" strength probably explains why the event was not accompanied by increased auroral activity. We've had a few aurora nights at 64N in the recent weeks, but this clear night showed none (bummer).

My friend also stated that procedural routes have either to be purely VOR-based or defined (and approved by the authorities) as "separated", neither of which is common in Scandinavia any more.

Overflying traffic was not affected as they could easily be separated by altitude.

I have heard no report of affected GPS signals nor observed any unusual anomalies (on the ground) myself. Since GPS operate near MSSR frequencies, it would be expected that it too experienced anomalies. My speculation is that if GPS was less largely hit, the difference might be explained by the difference in signal travel direction between MSSR (effectively horizontally) and GPS (more slanted towards vertical, even at 60+ deg north).

His comment that the radar system can filter out strong disturbances intrigues me. Could this be an "automatic" effect because the return signal would appear outside some tight tolerance defined by the Mode A/C/S protocol or is it more likely it is handled in an additional software layer? Any comment from an RF/MSSR-knowledgeable person would be appreciated.

(Edit) The end result was that aircraft in the air were allowed to land but no domestic aircraft were allowed to take off. Don't know about international departures. Normal OPS were restarted after about 1.5 hours. (/Edit)

(Edit 2) After re-reading the media report of that day (http://www.dn.se/nyheter/sverige/sol...ll-radarstopp/) I can add the following: All radar stations that were affected had the sun above the horizon. All false radar echoes appeared within an 8 degree narrow sector in the sunward direction. (/Edit 2)


kcockayne 8th Nov 2015 14:06


I could not agree with you more ! I know that the statistics give comfort to "those that matter", but they give no comfort to me. As I have said before, my generation of ATC was schooled (& submersed) in the "when the system fails, it fails safe" philosophy. For me, it is difficult to imagine that this philosophy is upheld in modern systems & methods. However, it is difficult to accuse those in charge of having a cavalier attitude in this matter when the statistics do not make an obvious flaw in safety standards apparent.
I do believe that there is such a flaw underlying the system, but it may never make itself obvious to the ANSPS, the regulators, the bean counters, the general public, or even to the ATCOS. Long may that continue to be the case !
In general, it may have to be accepted that the modern system & philosophy of ATC is the ONLY way to deal with the traffic load. In that case, "Goodbye Procedural ATC".

exlatccatsa 8th Nov 2015 15:26

Sumburgh, Shetland Islands also had a radar outage for about an hour at the same time.

Klauss 9th Nov 2015 08:31

hmm, shetlands, too ? Well, they are about at the same N latitude as Sweden.
I wonder why Norway and Denmark didnīt have Problems... Found a solar Radio
burst on https://twitter.com/thesuntoday , but donīt know if it is relevant

Re procedural control: canīt really remember having flown that for real during the last decades. So, no real practice - and I donīt think that todays traffic could be handled procedurally.....in London, Frankfurt, Stockholm...


NiclasB 9th Nov 2015 13:35

Klauss, thanks for the link. The timing and length of the event in the plots is consistent with the outage. Too bad that the monitored frequencies stop at 400MHz, but it stand to reason that the 1GHz band was affected too.

oblivia 10th Nov 2015 05:25

This is fine, particularly for the beancounters who have a great say in how airlines are run.
The chief executive runs the company 100%. Except when someone needs to be blamed.

Klauss 10th Nov 2015 06:03

I think so, too, but I am still looking for evidence. There are a few other stations that Monitor to 800 Mhz, but they donīt seem to have the same burst . No idea why....not a scientist....

MrSnuggles 10th Nov 2015 12:56

I wrote about this in the Nordic Forum when it happened.

The people from Luftfartsverket claimed that the solar flares disturbed radar enough that it would sometimes show doubles of planes, and sometimes the planes disappeared.

The disturbance lasted about four hours plus minus. It was low intensity flares so the automated system didn't filter the erroneous data because it was calibrated for larger events.

Klauss 11th Nov 2015 08:53

thanks for the hint - the newspaper article makes it clear that the SSR was in trouble, not the real radar. Looks like a strong radio burst fromt the sun played a role, but I guess the definite failure reason will take some time to determine.

DIBO 11th Nov 2015 11:17

and FR24 wasn't in trouble either :):)
Joking apart, a bit strange that Mode S - ADS-B based flight surveillance info (provided by 'consumer product' class of hardware) was available, without AC appearing tenfold. And top notch professional SSR was having trouble.
And the Olso boys and girls (left side of the picture) didn't seem to care either, while Swedish airspace was emptying out.

MrSnuggles 11th Nov 2015 11:34

That is why scientists are questioning the solar flare theory, DIBO.

I do not have access to the systems used on ARN et al, but I do know they have had some small problems now and then, ARN even had to close for a few hours and then a NOTAM to always carry enough for diversion was placed. (This was maybe a year ago, the NOTAM is lifted now...)

It is, in my mind, very possible that this might have been a glitch that happened to manifest during a solar flare, instead of the solar flare causing the glitch. The strange distribution of the flares and the complete lack of flares in Norway and Denmark is indeed very puzzling.

Klauss 11th Nov 2015 16:00

well, yes, itīs curious that there wasnīt anything wrong in the surrounding countries.
I still believe that the sun had a great deal to do with the Event. There was a medium strong disturbance going, in all aspects (ionosphere, magnetic etc.) and on top, there
was the Radio burst. It was even registered in Finland. Links:
The swiss observatory had it, too, including 1000.....1250 Mhz whichis where the SSR works.

So....some electrons found a way thatīs not ok, and therefore, SSR failed.

SSR ? Well, the describtion in the newspaper article from sweden....says as much.Hight info, identification...

Interesting subject.

eglnyt 11th Nov 2015 18:08

the newspaper article makes it clear that the SSR was in trouble, not the real radar
Whilst I know some who would claim that SSR isn't real radar in most places it is the main ATC radar and often the only ATC radar. Does anybody know whether there is Primary Radar in this area and if so was it also affected?

a bit strange that Mode S - ADS-B based flight surveillance info (provided by 'consumer product' class of hardware) was available, without AC appearing tenfold.
Not strange at all when you consider how they work. Both SSR and ADS-B have their weaknesses some of which are common to both. This set of circumstances exposed one of the weaknesses of SSR not present in ADS-B, there are other foreseeable failure modes which would only affect ADS-B.

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