Re: Boeing 737 and 737 MAX software

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

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])


-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
	wlfraed@ix.netcom.com