Re: [SystemSafety] RE : Qualifying SW as "proven in use"

From: SPRIGGS, John J < >
Date: Thu, 27 Jun 2013 11:52:44 +0000

When Peter's contribution arrived, I was drafting a reply to Matthew's posting that also justified the use of statistical techniques where failures are systematic. I will not bother with that justification now, but I will add a bit of advice for Bertrand's postulated safety-engineering rôle-holder.

Once you have established a quantitative model, it is easy to continue working in terms of the numbers and disregard the, perhaps tenuous, correspondence with the real world. This is similar to the situation with qualitative models where one can be lulled into working in terms of a 'feeling', and not acknowledging real-world complexity.

Do not present analysis results with many 'significant figures' and do not use them as the sole focus of assurance arguments. Rather, use predicted failure rates and associated analyses to support your assurance arguments, be they for reliability or for safety.

Statistical methods are used for quantifying equipment and system reliability through the analysis of failure data. Due to the high levels of uncertainty involved, these analyses do not offer the level of precision that the engineering user may expect. Treating these highly-uncertain numbers in the same way as precise measurements is unsound and is likely to lead to false conclusions.


Usual disclaimer about my opinions not being those of my employers, clients, et alia -----Original Message-----
Sent: 27 June 2013 12:35
To: Matthew Squair
Cc: systemsafety_at_xxxxxx Subject: Re: [SystemSafety] RE : Qualifying SW as "proven in use"


If you are not the intended recipient, please notify our Help Desk at Email isproduction_at_xxxxxx immediately. You should not copy or use this email or attachment(s) for any purpose nor disclose their contents to any other person.

NATS computer systems may be monitored and communications carried on them recorded, to secure the effective operation of the system.

Please note that neither NATS nor the sender accepts any responsibility for viruses or any losses caused as a result of viruses and it is your responsibility to scan or otherwise check this email and any attachments.

NATS means NATS (En Route) plc (company number: 4129273), NATS (Services) Ltd (company number 4129270), NATSNAV Ltd (company number: 4164590) or NATS Ltd (company number 3155567) or NATS Holdings Ltd (company number 4138218). All companies are registered in England and their registered office is at 4000 Parkway, Whiteley, Fareham, Hampshire, PO15 7FL.

The System Safety Mailing List
systemsafety_at_xxxxxx Received on Thu Jun 27 2013 - 13:52:57 CEST

This archive was generated by hypermail 2.3.0 : Tue Jun 04 2019 - 21:17:05 CEST