[SystemSafety] Correctness by Construction

[Dewi Daniels]

Peter,

In my paper, I explained that high G-force was removed as a condition for
MCAS to trigger, meaning that MCAS would now be activated by a single AoA
sensor and that the maximum authority of MCAS was increased from 0.6
degrees to 2.5 degrees each time it was activated.

Yours,

Dewi Daniels | Director | Software Safety Limited

Telephone +44 7968 837742 | Email d <ddaniels at verocel.com>
ewi.daniels at software-safety.com

Software Safety Limited is a company registered in England and Wales.
Company number: 9390590. Registered office: Fairfield, 30F Bratton Road,
West Ashton, Trowbridge, United Kingdom BA14 6AZ


On Fri, 10 Jul 2020 at 12:24, Peter Bernard Ladkin <ladkin at causalis.com>
wrote:

>
>
> On 2020-07-10 12:24 , Dewi Daniels wrote:
> >
> > There is no evidence that the MCAS software failed to satisfy its
> requirements. It appears that the
> > MCAS software behaved correctly according to its requirements, but that
> those requirements specified
> > unsafe behaviour. It seems that the system safety engineers and the
> requirements engineers only
> > considered a single activation of MCAS. They do not appear to have
> considered the possibility that
> > MCAS could activate repeatedly, eventually driving the stabilizer to a
> fully nose down position.
>
> The Congressional report also makes it clear that the company also altered
> the activation conditions
> of the (sub)system (which Boeing still calls a "function" of the STS),
> without either revisiting the
> hazard/risk analysis or informing the regulator.
>
> PBL
>
> Prof. Peter Bernard Ladkin, Bielefeld, Germany
> Styelfy Bleibgsnd
> Tel+msg +49 (0)521 880 7319  www.rvs-bi.de
>
>
>
>
>
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