From: gneuner2@nospicedham.comcast.net   
      
   On Sat, 6 Apr 2019 11:08:30 +0200, Terje Mathisen   
    wrote:   
      
   >George Neuner wrote:   
   >> On Fri, 5 Apr 2019 21:33:13 +0200, Terje Mathisen   
   >>  wrote:   
   >>   
   >>> The preliminary report from the ET flight (the second crash) indicates   
   >>> that the pilots knew about the emergency procedures to be used in case   
   >>> of MCAS trouble, applied them and still could not avoid a nosedive.   
   >>   
   >> I heard a report that the MCAS system was re-engaged *after* being   
   >> turned off.  The report indicated that investigators did not know   
   >> whether the pilots did this intentionally or whether it happened   
   >> automatically.   
   >>   
   >> Boeing's advice to pilots says that if there is a need to turn it off   
   >> in the first place, that it should be left off.   
   >>   
   >> The questions now are: can the damn thing actually be turned off? And,   
   >> if so, did the pilots turn it back on for some reason?   
   >   
   > From reading comp.risks it seems like there are two levels of turn off   
   >MCAS and at least three different switches/buttons:   
   >   
   >The first level turns off MCAS by immediately resetting it,   
      
   MCAS can be overridden temporarily by pulling back on the yoke.  But   
   if it simply overridden it reengages after several seconds if the   
   computer thinks the plane is still in danger of stall.  To turn it off   
   there are a pair of switches on some panel.   
      
   >the problem   
   >is that when it comes back on (automatically) it has also forgotten that   
   >the tail surface as already been depressed, so as soon as it gets   
   >another bad reading from the broken angle of attack sensor it will send   
   >additional commands to further depress it, increasing the problem.   
      
   Interesting ... that I hadn't heard.  That would be quickly fatal   
   because the tail depresses 10 degrees with each activation.  Beyond 40   
   degrees the attitude would be unrecoverable below ~10K ft.   
      
      
   >> Early on the Airbus 300 suffered from a issue involving "go-around"   
   >> (aborted landing) behavior that caused multiple crashes.  In the case   
   >> of the Airbus, the method to override the "feature" was different in   
   >> different models - and in a split-second emergency the pilots had to   
   >> be aware of which model they were flying.   
   >   
   >Ouch. :-)   
      
   Yeah.   
      
   >   
   >Terje   
   George   
      
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