Re: [SystemSafety] SIL ratings to be scrapped?

From: Peter Bernard Ladkin < >
Date: Sat, 24 Aug 2013 08:57:21 +0200


Matthew,

On 8/24/13 5:55 AM, Matthew Squair wrote:
> That take up may be based more on a lack of understanding of its utility in non process control
> domains (low IMHO) or a judgement that it's an easy 'compliance = safety' argument that can be sold
> to defence customers who love a standards approach...
>
> On Friday, 23 August 2013, RICQUE Bertrand (SAGEM DEFENSE SECURITE) wrote:
>
> It is interesting to see this evolution in UK while at the same time the major defense operators
> (DCNS, Nexter, EADS, ) in France are adopting IEC61508 straightforward and including it in
> their requirements, included for retrofits ____

To the contrary, it is based not on any lack of understanding but on straightforward market mechanisms.

Suppose you want to buy a washing machine, a very good washing machine, maybe the best. Then you might look to Miele, just down the road from us (there is a plant here too, but washing machines are down the road). It comes with a plug for German-standard house electricity supply. Suppose for the sake of this analogy that changing the plug is *very expensive*, costs, say, on the order of the price of the machine itself. And it's not just a washing machine you want, but all other household kit too, from other countries as well as Germany and your own. Now, nobody else's plugs fit your sockets and your plugs don't fit theirs. What do you do? Well, first you give thanks that you're all on 230-250V and 50-60Hz. Then you don't pay for all those plug changes, you just go buy adaptors. Because otherwise it would cost you twice as much.

This only works, though, if (a) the common grid values are some approximation to an adequate electricity supply, and (b) there exist adaptors.

Here is the translation. Common grid values = international standard. Local plugs/sockets = local military procurement standards.

Most major defence contractors have multiple clients. Most have, let us say, First Customers: the First Customer of a US company is the US military, that of a French company the French military, of an Indian company the Indian military, and so on. Successful military equipment suppliers supply clients other than their First Customer.

Clients want kit developed to a standard, preferably their own. Suppliers have developed kit to a standard, or multiple standards, but not necessarily the one Client uses, unless Client is the First Customer.

So what is going to happen? Client wants to buy; Supplier wants to sell. It's going to happen, hope both parties, but there is that pesky thing about standards conformance, which is usually a legal requirement.

Somebody is going to have to put up the resources (i.e., pay) for Supplier's kit to be retroassessed to Client's standard. This can cost huge amounts and be very tricky. For example, the UK military's attempt to retroassess the C130J was a massive attempt involving innovative engineering methods and can only be regarded as partially successful (see the German/Daniels project on the SW, for example). And the entity putting up resources is ultimately Client. If you screw up the contract, for example on Mk 3 Chinooks, Client doesn't get the info it needs to assess conformance to local standard and consequently cannot use the kit as desired.

One might thereby think it useful for Client to have a local law which says: if it's US MIL STAN it's good enough for us. But that is not what local law says in most developed countries. And there may be good reason for that - it may not be true! See, for example, the controversy over the quality of the aforesaid C130J SW. And, besides, such a law only works for Supplier from a specific country. You'd have to have a similar Client law for other countries with Suppliers, and then Client would basically be saying "if it's developed to some military standard somewhere, it's good enough for me". But would such an attitude be enough to assure fitness for local purpose? Who knows? And counterexamples abound. Look up, for example, "Chinook" and "Mull of Kintyre" and read doubts expressed by UK military investigators about the quality/safety of the control system of one of the world's workhorses.

So what's easiest and cheapest while being effective? There is an international civil standard, for better or worse. Suppose Client has good local understanding of how its local standard relates to that international standard; maybe even has a rough translation algorithm, leaving out some Sharp Points. Suppose Supplier has developed kit to that international standard and provides the accompanying documentation. Then Client pays locally for the translation which it knows how to do, leaving Sharp Points. Supplier and Client just have to address Sharp Points. Likely to be much cheaper all around.

Eventually, even First Customer understands that Supplier is developing to IEC 61508 anyway. Rather than insist on its own local standard being applied in parallel, on each development, First Customer invests once in a rough translation manual. And on each new procurement, applies the translation manual, and Supplier and First Customer file off Sharp Points. Much less expensive in the long run.

And much less wasteful of resources for the world, too, as a whole, unless you adhere to a religion which regards the generation of paper as being the most holy of human activities, like the remnants of the Prussian state......

The success of such an approach, though, does rest on above caveats (a): that objectively the international standard is mostly adequate for most military system safety purposes; and (b): applying the translation manuals plus filing off the sharp edges mostly works. That may or may not be the case. But to set the mechanism in motion, all that is required is that sufficiently many people *believe* both (a) and (b).

PBL Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany Tel+msg +49 (0)521 880 7319 www.rvs.uni-bielefeld.de



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