A few posts since I was here last.
I know too many pilots/operators whom are less than diligent when recording flight times.
Indeed. That is a REAL worry when it comes to continuing airworthiness matters. Keeping to the bucket of life fatigue analogy, if you don't keep the odometer working, it all turns to custard .....
Cessna do not seem to publish much data in regards to specific airframe life limits.
Although things have changed over the years, in the earlier days, light aircraft didn't get much worry spent on their longer term service history and fatigue considerations. More effort was directed to heavier aircraft. Interestingly, Australia's DCA was a leading light in fatigue work going back quite some years and ran some very valuable Industry monitoring programs with specific aircraft. We had some very expert structural folk in DCA - Max, Col, Martin, Bruce and others.
the finite limits even two mass produced planes may snap at slightly different tolerances,
Absolutely. Fatigue work is a very rubbery, statistically driven area of engineering. The published numbers are based on pretty conservative work up data and, in reality, the aircraft shouldn't go "bang" anywhere near those figures. However, if the engineering workup is flawed (usually due to imperfect state of the art understanding - think Comet), or if the recorded history (or usage patterns) is substantially in error, then it becomes a case of all bets might be off or, at the least, things become a bit suspect.
so you can only go by what it's certified to do and act accordingly.
Every pilot should read this bit several times over. The whole thing depends on the certification's getting things pretty right, then the history's bearing a reasonable validity compared to what the OEM presumed might be the case or, if it doesn't, having that information fed back through the airworthiness authorities to the OEM, or directly. Much of the problem is that the pilot training programs don't get anywhere near this stuff, so the average pilot knows schmick about it. This is why we put effort into these sorts of threads in PPRuNe.
Problem is when you have ice and other things involved
Aircraft design and operation is based on a lot of statistical presumptions which work, pretty well, overall. However, it certainly is more than possible to get into awkward situations where you are getting out on a limb. Planning, monitoring, etc., is the best defence a pilot has against this sort of problem.
The point with the ATR saga
Conspiracy aside, one of the problems is that the folk involved throughout are human and humans make mistakes. The aim of the system's safeguards is for such mistakes to be detected and corrected where appropriate. Sometimes this takes some lessons learned in blood along the way.
One thing I noticed from recent transport category events
Which is why I despair when I see new folks who have nil interest in learning more than the absolute bare minimum to get through exams and endorsements ....... It's a bit like poverty - unless you do something to break the cycle it just perpetuates and stays down in the mud.
Metal fatigue and corrosion are two different things.
Yes, but related in that corrosion can accelerate fatigue problems greatly, quite apart from having the potential to affect, adversely and directly, static strength by eating away at the tin bits.
'unexpected' cracks start appearing in places that were not designed to bear the greater loads imposed
That's one of the worries with fatigue if the OEM doesn't have the out-there-in-Industry usage data.
For those who might like to read up further, search the net for "static structural loads", "dynamic structural loads", and "structural fatigue".
We do have a few structures experts in the sandpit. Hopefully, one or more might be motivated to wade into the discussion.