[SystemSafety] Fwd: Rethinking Safety and Security/11 PCB Layout Myths

[SPRIGGS, John J]

In some parts of the aerospace industry, you need to have assigned an assurance level, and done the necessary, in order to get the thing into operation so that you can start collecting the field data in support of your operational experience claims.  So, no, operational experience and testing does not qualify you for a DAL, but a DAL may require you to make claims on operational experience and testing.

John

-----Original Message-----
From: systemsafety [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of Peter Bernard Ladkin
Sent: 08 December 2016 09:32
To: systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] Fwd: Rethinking Safety and Security/11 PCB Layout Myths

David and Mario,

Dictators, monarchs and elected prime ministers are "comparable but not the same". They all run the country. Would you like to argue that there aren't essential differences?

Suppose you have some software whose performance you have assessed through operational experience and testing. You know to 95% confidence that the software has a failure likelihood of less than 1 in
10^(-6) per operational hour.

Question 1. Can that qualify the software for a DAL?

Question 2. Can that qualify the software for a SIL?

Answer to 1: No. A DAL varies the confidence level (higher DAL; more confidence needed), but the requirement in 14 CFR 25.1309 and CS-25.1309 is that any component performs as specified.

Answer to 2: Maybe or maybe not. The reliability requirement for SIL 1 is satisfied. But there is nothing in the standard about what confidence level is needed. Maybe 95% is OK with some assessors and not OK with others.

PBL

Prof. Peter Bernard Ladkin, Bielefeld, Germany MoreInCommon Je suis Charlie
Tel+msg +49 (0)521 880 7319  www.rvs-bi.de

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