Re: Boeing 737 and 737 MAX software

[russ lyttle <lyttlec@removegmail.com>]

On 4/22/19 3:36 PM, Norman Worth wrote:
> Dennis Lee Bieber wrote:
>> On Thu, 18 Apr 2019 06:53:10 -0700 (PDT), tranngocduong@gmail.com 
>> declaimed
>> the following:
>>
>>>
>>> a) Ada was used but programmers have chosen a wrong (too relaxed) 
>>> subtype, or other language was used and programmers failed to code 
>>> whatever equivalent to raising and handling a CONSTRAINT_ERROR. 
>>> Simply: software bug.
>>>
>>
>>     The common action on any exception is to log it (in flash memory) and
>> /restart/ the FMS software. Restarting likely includes synchronizing with
>> the second FMS -- but after such a synchronization, aircraft control 
>> would
>> have been given to the primary FMS; which likely would have almost
>> immediately produced an exception and.... repeat until the pilots 
>> manually
>> switch control to the second FMS processor.
>>
>>> b) Contrary to general belief, the software was not programmed with 
>>> multiple redundant computation. Simply: process failure.
>>>
>>> I chose to believe a).
>>
>>     It is most likely a variant of B. MCAS was supposed to nudge the
>> aircraft attitude when it sensed a potential stall condition from just 
>> AoA
>> (airflow angle against the wings) with no concern for air speed;
>> pre-existing air speed computations were not changed by the addition of
>> MCAS (couldn't have been if MCAS can be manually disabled in flight).
>> Without the (formerly optional) hardware, this becomes a single sensor
>> matter -- and one which can not be detected as faulty (while each FMS may
>> have had its own sensor, during a disagreement, the primary FMS likely
>> pushes /its/ computed aircraft state to the secondary FMS which is 
>> supposed
>> to start computations from those values; probably diverging again 
>> until the
>> next sync interval -- get enough of these divergences and the secondary
>> might be the one to shut down; the FMS displays might show "SINGLE FMS"
>> mode])
>>
>>
> A good programming language will not compensate for a bad system design!
Been trying to convince management of that for almost 50 years. No luck.