PPRuNe Forums - View Single Post - Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed
Old 1st May 2019, 23:24
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Loose rivets
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I hadn't read that AV item before. Frankly, I'm going to have to go back to it several times to absorb it in its entirety.

By this, I mean the not-quite-so-easy-to-understand second cut-out switch circuitry. Is this contained overview statement correct? Grief, no wonder it wasn't understood in a iPad ramble. Even after a lifetime's love of electronics, stepping on that aircraft and truly understanding the systems would be a serious challenge.


The quotes are one question, split, and in reverse order.


Again, one of the main bee-in-my-bonet's issues. Just what is the truth about that second (underfloor) column switch? I know, it's the third time I've shouted that question.

17 - On the 737 NG aircraft any autotrim can be stopped by just moving the control column in opposite direction (e.g. an autotrim nose down is stopped by a nose up control input). However, on the 737 MAX aircraft this stop has been completely disabled for MCAS to operate, hence, a trim movement can no longer be stopped by opposite control column movement causing substantial startle effects on flight crew (based on sim instructor experience).

In addition, the MCAS on MAX can not be stopped by the control column trim cut out switches, only the cut out switches at the center console, while on NG autotrim could also be permanently stopped by the cut out switches at the control column without disabling manual electric trim on NG aircraft. Would the FAA not agree, that this is a very significant difference between the aircraft, that could cause a crew to lose control in time critical stages of flight? Was this risk assessed during certification of the MAX systems?
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