Originally Posted by
gums
Salute!
Thanks for the input, PEI
OTOH, we see many raw data flight data recorder traces and have had super analysis amongst us, especially on the Tech Log. So seeing the data is not without precedent here, although the masses that read the New York Slime would not have a clue ( as they do not about many things)
My point and maybe Stri and FDR and Edmund , et al be that the plane may be just fine at idle thrust versus high thrust or even cruise settings. How bad is the linearity? And I do not believe "Peter" has the actual plots from flight test data, Finally, the change to the amount of stab movement, etc after the initial implementation is, or should be, of interest to all of us.
And "all of us" includes old farts like me that are now only SLF. As a SLF I once got a free bottle of champaign from the Western airline crew ( back a long time ago before being absorbed) for commenting to nearby SLF that the crack maintenance folks were repairing a hydraulic leak on the left main gear brakes. We had to delay about a half hour, and the nearby SLF were getting restless, heh heh. Crew told me that my commentary helped calm down the SLF and made things easier for all.
I may only be a knowledeable piece of SLF nowadays, and it scares me more than the average piece sitting next to me when I see what this MCAS debacle has wrot.
Gums sends, and Merry Christmas to all!!!!
Gums,
Math jargon Sri’s , “may exhibit non-linear feedback” is the engineer’s equivalent of saying may become EXTREMELY unpredictable.
- one wants a system to be controllable - ie can be brought/forced to a desired eg. nice stable state starting from any state inside the envelope.
- if the system is “linear” then a branch of engineering maths called LINEAR control theory applies, the domain where it is controllable is known, and eveything is “copacetic”, automation can be easily used, and the system may be approved on the virtues of its design.
- if the system is “non-linear” and even worse if it exhibits non-linear feedback, then can as they say in the US it can “go postal”, and standard school maths can’t describe it nor control it. An auditor won’t certify such a system unless it is extensively tested -if the auditor be honest. And automation can be very unhappy about the surprises baked into such a unpredictable system.
The suspicion is that MCAS is there to keep the MAX centered in an envelope where it appears linear, but that without MCAS it might get into states where it would be really hard to control (except for Chuck Yeager and you). The unfortunate joke is that the extant MCAS took several airframes into states where they were hard to control. Of course one could argue one can always deviate into a non-linear behaviour eg. stall, but the suspicion here is that the volume of linearity is more limited than it should be, and that really ugly things happen in places where certified airframes should still be acting nice.
I’m sorry if the above is erroneous or unclear, my opinions are usually worth exactly what people are paying for them.
Merry Xmas