Originally Posted by
CONF iture
1) To work properly, automation and protections need reliable data.
If data are known to be corrupted the simplest thing to do would be to cancel automation : Direct law - No autotrim
Every Boeing pilot flies that way in manual flight, is it an issue ?
Yes it is an issue.
At Schipol the 737 autotrimmed into stall and trim was never touched in recovery (nor was thrust properly applied, but had it been the result might have been worse due to trim - see e.g.
http://www.pprune.org/rumours-news/3...ml#post4787036 ).
Ethiopian (boeing again...) at Beirut was mistrimmed, manually, into stall and crash.
At Perpipnan they did drop into direct law... and it didn't help. They were trimmed up into stall and never changed it. Had they stayed in alternate with auto trim would they have managed the recovery ? Would autotrim have helped or hindered them ?
2) ALT LAW + Autotrim amplify the severity of the stall.
Surely only if the stick is held back, which will be fatal anyway in stall ?
On the other hand if stick is pushed forward, autotrim (if trim was NU into the stall) will help to reduce AOA and reduce chance of secondary stall when compared with not touching the trim, no ?
PS : Thanks to both of you for you reply.
It is unacceptable the BEA simply ignores the matter.
There is a difference between ignoring a line of investigation and investigating, eliminating and not pursuing further. The auto trim behaviour clearly has been investigated, based on what is in the report.
Resources are finite, and I don't think the investigation necessarily has the remit to go further into things that may be interesting but not causative or relevant to the outcome of the accident. There are areas I'd have liked more depth on - but I think they've eliminated them too.
My impression looking at the HF slant in the report is that BEA have clearly focused on (1) rather than (2) from:
(1) why are crews (not just this one) stalling and pulling back in stall
(2) why is the trim following the pilot command when (1) happens
So, are they correct to prioritise (1) over (2) - which does not mean they ignore (2) - which problem needs fixing to prevent crashes ? Which problem will become a non-problem if the other is fixed ?