[SystemSafety] Fwd: Rethinking Safety and Security/11 PCB Layout Myths
SPRIGGS, John J
John.SPRIGGS at nats.co.uk
Thu Dec 8 09:58:33 CET 2016
For RTCA/DO-178 and ED-12 the software level is associated with the severity of the risk, other schemes use levels based on risk 'likelihood' and are thus orthogonal.
John
-----Original Message-----
From: systemsafety [mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of David MENTRÉ
Sent: 08 December 2016 08:20
To: systemsafety at lists.techfak.uni-bielefeld.de
Subject: Re: [SystemSafety] Fwd: Rethinking Safety and Security/11 PCB Layout Myths
Hello,
On 12/08/2016 06:35 AM, Peter Bernard Ladkin wrote:
> Wong makes the common mistake of formulating equivalence between
> "levels", here the Design Assurance Levels (DAL) of avionics with the Automotive Safety Integrity Levels (ASILs) of ISO 26262.
I would make the same mistake.
> DALs are criticality levels. How critical something is to the
> operation of the system, and therefore what level of assurance to which it should be subject.
>
> A SIL is a reliability requirement on a safety function. A safety
> function is something whose action reduces an unacceptable risk of a
> specific hazard to an acceptable risk. It operates as designed only if the reliability requirement set by the SIL is fulfilled.
>
> In principle, all safety functions have the same criticality: they are
> all critical, period. So, one criticality level, rather than the five of ED-12C.
[disclaimer: I never looked at ED-12C / DO-178C text.]
So all SIL A to D of ISO 26262 would correspond to one DAL of EC-12C?
Which one? DAL A?
If this the case, why make the difference between several "sub-DAL-As"
in ISO 26262?
From my software engineering point of view, ISO 26262 SILs and EC-12C/DO-128C DALs are the amount of work to reach a certain level of quality of the software, and in that sense are similar.
Best regards,
D. Mentré
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