Originally Posted by BOAC
I'm struggling to see [my comment]
as a gratuitous insult. It is simply a statement of opinion based on observation.
Well, I don't believe that. I think you're just trying to needle.
Originally Posted by BOAC
As an (expert) 'end user' I (and others) happen to find 'raw data' a major factor in the 'Safety of Aviation'
Another statement of opinion, I suppose. Let's see if this one is any better. Can you name any accidents in which a crew's inability to fly on "raw data" was a factor? (Note this is a very specific question.)
MB is puzzled about the use of Bayesian techniques in the evaluation of (supposedly-) ultrareliable systems. His response to the comments I am offering is to imagine I am being argumentative. I get enough of that kind of banter from the people I live with, the cats and the ex-ladyfriends. Can we get back to pretending we are professional people with certain sorts of expertise having a technical discussion?
Originally Posted by BOAC
To me (as a pilot) ["raw data"] means that although the data has passed through many ICs and the like it is essentially the 'truth' and not some software programmer's interpretation of what he/she THINKS I should be seeing
Let me say it again, just in case it wasn't clear enough the first time around. According to this explicit definition, very few airline pilots on modern kit see any "raw data".
Now, let me turn to querying the definition of raw data. RAs fall over every so often. They don't appear to use BITE (or, not effectively) and standard fault-tolerance methods don't appear to be used with multiple RAs in certain kit (say, Turkish Airlines's Boeing 737NGs). The generic failure rate is, I guess, somewhere between 1 in 10^(-4) and 1 in 10^(-5) per op-hour. According to the definition above, a Turkish Airlines RA on approach to AMS a couple years ago ceased providing true data rather abruptly. So, according to the definition above, the question arises: when you are looking at a "raw-data"-delivering instrument, such as a VSI, ASI, or altimeter, how do you know you are getting "raw data"?
I actually think the definition above is wrong. And I think it can be partially fixed with a little thought. And I think that, when you try to fix it, you will maybe get some initial inkling of the problems associated with reliable data-paths. All that is then needed to make my general point about modern kit is to interpose a couple of computers.
PBL