From: terje.mathisen@nospicedham.tmsw.no   
      
   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, 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.   
   >   
   > 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. :-)   
      
   Terje   
      
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   -    
   "almost all programming can be viewed as an exercise in caching"   
      
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