For something like flight data I'd expect there to be some sort of public announcement from the airport concerned, which is probably what that website is using as its primary source.
Not even close! The data is collected from the aircraft transponders using automatic dependent surveillance-broadcast (ADS-B) receivers. Flightradar24 has a network of more than 20,000 ADS-B receivers around the world that receive flight information from aircraft with ADS-B transponders and send this information to their servers.
The information is copyrighted. Use of it for other than transitory viewing is forbidden by their licence. The original poster needs to ask their permission unless there is some limited exception in the relevant Swedish law. IAAL.
I am fully aware of that. But if you go back through the thread you will find
> It the flight data presented for an airport.
...and "flight data" in the context of an airport is usually interpreted as arrivals and departures, as distinct from aircraft movement.
Now, I fully accept that if the information being presented is /entirely/ derived from monitoring the planes' transponders that the website operator has some claim to it. But OP is specifically saying that it is airport data, and I'd expect aircraft arrival and departures to be published accurately by the local controllers: (a) as a matter of public record and (b) to comply with their responsibilities to controllers in adjoining countries (even if that is treated as privileged in the country of origin, a close parallel being UK Met Office observations).
In addition to that, one has to ask whether Flightradar24 really is legally entitled to receive that transponder information, since if they aren't it might be difficult for them to make copyright claims stick. Specifically, in the UK there certainly used to be a paragraph in the wireless regulations (back in the day when one got them from Waterloo Bridge Road) which prohibited receiver owners from using their equipment to monitor non-public transmissions: I believe that one is still supposed to not listen to aircraft bands (unless authorised to use them) and it would be entirely reasonable to extend that to aircraft (etc.) transponders.
Now I'd be the last to challenge Flightradar24, since I believe that they provide a useful service (and a fascinating one, if one is that sort of geek). But in the general case I believe that my point applies: factual information can't be copyrighted, in the same way that statements of fact can't be patented. But details of layout, even something as trivial as the number of decimals or the choice of columns to appear in a table, can. As, obviously, is their choice of adverts and the commercial relationship they have with their advertisers, which is really what their copyright is all about.
MarkMLl