How the Boeing 737 Max disaster looks to a software Developer

Re:How the Boeing 737 Max disaster looks to a software Devel... by metanoia on Friday April 19, 2019 @01:56AM (#19697389)

One question I've had is why Boeing changed the design of the stab cutout switches from the 737NG from a pair of switches - the right side switch that disabled the autopilot control of trim and the left side that disabled the trim motors entirely [1] - to a design with a similar pair of switches, but each controlling the primary and backup control motors of the elevator trim [2] instead of controlling the source of the input. (If you look closely at the yoke trim switches, there are two independent switches that are grouped together by a frame so that they move simultaneously. One drives the primary motor, and the other the secondary).

Assuming they'd kept MCAS on the switch associated with the automatics, the procedure would have been to throw the AUTO PILOT switch, disabling MCAS, but keeping the MAIN ELEC switch on, allowing them to trim back to neutral for that speed.

[1] https://www.airliners.net/photo/Australia-Air-Force/Boeing-7...

[2] http://www.b737.org.uk/mcas.htm#stcs

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Re:How the Boeing 737 Max disaster looks to a software Devel... by metanoia on Friday April 19, 2019 @01:32PM (#19701350)

EDIT: Oops, there's only one trim motor on the NG. Both trim switches must be actuated on the yoke switches though. But the input cutoff switches still work the same way I originally stated.

Not sure about the Max's # of trim motors, but the Max definitely doesn't have input source cutoff switches.

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