Such a shame to hear about this today, so awful and sad. I will add a few of my 2 cents to what has already been said.
Correct me if I'm wrong but Jetline seems to be one of the few original trained-schwarzkopfs (of this type so discounting the jetstars) that haven't had a big refurbishment/overhaul/new trains. As mentioned above Lisebergbanan had a big train overhaul (but you wouldn't notice if you didn't know because they're pretty much identical), Nessie had a similar overhaul, Alpina Bahn has got new gerst trains, Sooperdooperlooper has new gerst trains, Revolution has new trains, as does Riddler Mindbender etc etc, you get the picture. If not they're getting new trains old schwarzkopf trains can get manufacturer overhauls with stress testing and in-depth refurbishment. As Chris has mentioned, I'd be really interested to see if they've been stress-testing/checking for cracks with x-rays or whatever it is they use with Jetline. You'd think so, given it's age, but I'm not sure whether it's required in all countries or what the regulations are. I saw a comment somewhere saying it wasn't require in Sweden but this is completely un-supported by any evidence.
The wheel assemblies and their attachment points are going to be high stress points on any coaster so it makes sense that if anything were to fail it would be these after 35 years of high forces, especially if there's been no refurbishment, proper testing or whatever. Every ride will have high stress points. For example, I know Top Spins and Top Scans have areas where they have to be thoroughly checked for fatigue because of localised high stress. It depends on the nature of each ride exactly where these areas will be. Even the best engineered things have a shelf life and will fail at a certain point if they're put under high pressure for long enough. These coasters are old now and have strong forces so need significant TLC to keep them running.
The two earlier incidents both involved people not reading the maintenance manuals correctly. Mindbender was a translation issue and Quimera was, I believe, a total lack of manual, coupled with them running the coaster faster than it was designed to run (it was running with the mid-course break-run turned off). So, I agree it is surprising to see this kind of incident at a park like Grona. It you want to run one of these classic coasters these days you need to be spending the money on getting new trains or majorly refurbishing and overhauling the ones you have with new parts etc.
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