Originally Posted by
Bend alot
1 in 10 or 1 in 1,000,000 in "should be controllable? - in the last known "good position"
Originally Posted by
safetypee
As currently described / discussed, the modified preventative system appears only to be concerned with erroneous trim operation due to MCAS.
If so then the likelihood of a trim runaway in the Max would still be similar to the NG.
Are the risks associated with this still acceptable given the difficulty / impossibility of moving the trim as demonstrated by the accidents and elsewhere.
We are in uncharted territory, but my understanding of the Seattle Times article is that the "fail-safe" option is to do nothing to the horizontal stabiliser, in the event of contradictory inputs. This applies to both the old MCAS V1.0, and the newly tested fault configuration.
I have no idea what the relative risks might be, but this seems safer than allowing an uncommanded stabiliser trim runaway. Presumably the FCC software will still try to allow pilot-yoke electrical stabiliser trim, but there may be circumstances in which this also fails, in which case the trim wheels are the last option.
The impossibility of moving the stabiliser, have only been demonstrated when the aircraft is significantly out of trim. If there has been no uncommanded movement of the stabiliser, it is hard to see how this could happen. Perhaps some combination of flaps-up and changes in engine power?
As earlier comments have suggested, we only seem to have half of the story.