Re: [SystemSafety] Fault, Failure and Reliability Again (short)

From: Mike Ellims < >
Date: Wed, 4 Mar 2015 21:58:20 -0000

Hi Martyn,

I can't really answer that as the project unfortunately died before we got that far.
However the initial phases of addressing the problem were investigated using FTA which suggested all the critical items had to be replicated to have a realistic chance of actually meeting the requirement; as opposed to hand waving.

The interesting bits e.g.
- using non-aerospace components (e.g. automotive alternators). - maintaining forward compatibility i.e. if a processor is available for 5 years how do you keep a system in production without stocking up on parts - Etc.

Weren't really addressed.

However from a reliability point of view the digital electronics were almost the least of the problems. Analog electronics is more problematic and some of the mechanical components were "interesting" as well.

-----Original Message-----
From: systemsafety-bounces_at_xxxxxx [mailto:systemsafety-bounces_at_xxxxxx Martyn Thomas
Sent: 04 March 2015 16:20
To: systemsafety_at_xxxxxx Subject: Re: [SystemSafety] Fault, Failure and Reliability Again (short)

That's very helpful, Mike.

What evidence do they consider adequate to demonstrate 10^(-9) for digital hardware?
And do they specify a confidence level for the probability?



On 04/03/2015 15:58, Mike Ellims wrote:
> Some time back I had the opportunity to sit down with the heads of the
> FAA certification panel (we were doing something unusual) and we
> discussed this to a great extent. The outcome is that for the purposes
> of certification the failure rate of software is not considered as the
> FAA do not believe it possible to reliably calculate a failure rate for
> The figure of 10^(-9) applies ONLY to hardware; software is required
> to meet the process/quality requirements as given in DO-178 and
> verified means of audit (i.e. they come in and work you over ;-).

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