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Old 31st Dec 2022, 00:34
  #118 (permalink)  
john_tullamarine
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Good to see the thread generating a lot of interest.

A few comments, though.

Please keep in mind that all the mods are volunteer, part-time, itinerant folk who drop in when they can, and have the time. It is reasonable to expect some delays between any consecutive input from any given mod.

Unless I get overruled by those further up the food chain, my only request is that we don't identify people until that information is in the public domain media. There is no benefit to be had causing those left behind more grief and anguish than they already find themselves having to cope with. If necessary, mods can wield the big stick but I would hope that that is not necessary. On the other hand, robust discussion about this and that, in general, is a good thing and just might add to the body of general pilot knowledge which, often, can be seen to be lacking. Such discussion may have no direct relevance to this particular mishap but can contribute usefully to the general learning process. Indeed, some folk who push a particular wheelbarrow might well find themselves in a situation of embarrassment when the investigators' report(s) see the light of day.

As a mod, it is not my role to exercise an omnipotent guiding hand to the discussion and that, probably, would be a bit above both my paygrade and capability. All I am here to do is keep things reasonably cool, calm and collected. I might well disagree with comments I read but, again, that is not the point. However, I will keep things from getting too far out of hand regarding social propriety.

What really concerns me reading some of these posts is the simplistic expectations which some of our colleagues have about the aircraft they fly.

The reality is that an aircraft is designed on the basis of a load spectrum, turbulence spectrum, gust spectrum and so on with consideration of whatever design standard is relevant to the certification. There is no sensible basis for any presumption that one aircraft is as strong as another - on the one hand, put a specific aircraft in a situation where the external environment (eg thunderstorms) and/or pilot loadings (ie cowboys) are well outside the design envelope and it is going to go "bang". Further, if there is hidden fatigue damage, the "bang" trigger may be lower for some older aircraft. The tragic situation here is that the poor driver who gets killed usually isn't the cowboy who contributed to setting him up for the inflight disintegration.

However, where one aircraft will fail in a given set of circumstances, another might well survive. It is not a case of one story fits all circumstances. All the pilot can do to help things is to operate the aircraft sensibly and in line with what the OEM suggests in the POH/AFM.

The basic story is along the following lines and, if it seems that I am repeating myself, my apologies -

When the aircraft is new and released to service there is a high probability that it will survive fine if it is flown within the design expectations.

If the aircraft is

(a) overloaded modestly (ie much beyond the limit loads) for more than a few seconds, one shouldn't be surprised if things start to creak and groan, the odd bit bends and stays bent, rivets deform and pull out and so on.

(b) overloaded excessively (ie much beyond the ultimate loads - normally 150% of the limit loads) for more than a few seconds, one shouldn't be surprised if important things go "bang". If you haven't watched the Boeing video I linked to earlier, you should - it is quite illustrative of this part of the story.

Now, it is not a case of sudden cliffs (unless you fly straight into one - I recall a presentation where an impressive cliff, complete with an impressive big black smudge, indicated the last moments of, as I recall, a B1B) where, should you let your toe go beyond the edge you will die - there will be a little bit of fat as a result of the realities of the design process. However, as you can see with the Boeing video, that pad might not be more than a poofteenth or two. You certainly wouldn't stake your neck on unrealistic pilot expectations of what the aircraft might, or might not, do in reality. This stuff has a healthy serve of statistical expectation embodied so there will be a degree of rubbery-ness involved. Generally, the certification margins will cover that problem sufficient to let us sleep at night.

(c) oversped then the loading effects of turbulence and gusts are amplified and things could go pear-shaped very quickly. Should you fancy playing the hero above Vne by any significant margin, you run the risk of having the tin bits enter a dance competition mode - but just for a short period, often measured in split seconds - prior to becoming airborne Christmas tinsel.

Then you have the problems associated with operational history, especially structural fatigue. If the designer gets it right, the pilots do it right, and the maintainers do all their bits right, things should go along reasonably fine. This presumes, though, that the loading spectrum during that history is consistent with what the designer worked on. This is where the operators and the pilots, particularly, can make it a do or die outcome. The engineering world can go so far, but if we don't know what the aircraft has been "really" doing, then the sums get further and further away from reality and the continuing airworthiness expectations might not be able to achieve their intended aims.

When it comes to investigating a structural failure, the boffins can measure a lot of stuff and make a range of assessments. So, for instance, blind Freddy can see and assess a fatigue failure or a simple overload failure. What they might not be able to do is figure out the precise sequence of events on all occasions. So the idea of being able to know all the ins and outs of a structural failure might be a little optimistic.

What the pilot needs to make sure, is that he/she operates the aircraft in a manner consistent with the OEM's reasonable service history expectations. This means that we spend the very great majority of our time not too far away from 1g within a speed range which doesn't see us too much past Vc. It is presumed that there will be events which take the aircraft further into the depths of the VG envelope but, the further you get away from the routine operational presumption, the less and less frequent should be those excursions. If an aircraft is operated routinely in more turbulent conditions than the OEM expected or if the pilot pulls more g more often than the OEM expected, then the fatigue problems, especially, can escalate rapidly.

Fatigue can be thought of as a bucket full of aircraft structural life. Every time the aircraft moves into the higher g regions of the envelope, think in terms that you have just thrown an eggcup full of structural life out of the bucket. Eventually the bucket gets to be empty. Once you are in that region, it might only take a slight bump to set a static failure in motion and you might see the wings, or some other important bits, go "bang'. To suggest that ageing aircraft don't, occasionally, fail is silly - they do. However, if everyone has done their bit, appropriately, they shouldn't.

It's not all that difficult at the piloting level. If everyone does their bit and treats the aircraft with a bit of tenderness, we all have an increased probability of living another day ....

So far as the 210 is concerned, I've flown several models (although long ago) and found them a great little machine. However, as with any aircraft I strap to my tail, I do a bit of research into the TCDS and AFM to get a handle on what the OEM expects of me, as the pilot. You should do the same. If I'm in a normal category machine, I will have one set of OEM expectations, if in an acrobatic category machine, a whole different set of expectations. If I look at several normal category machines, they won't all embody the same set of expectations but, providing one knows the story adequate for operations, all should be well.

The worry is when folk don't give it any thought, just jump in and do whatever they think might be a fun thing ...
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