#31
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On the midday news, ET crew reported followed SOP (from Boeing) for MCAS issue.
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#32
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Bad software
As I understand it, MCAS was limited to 2.5 degrees of horizontal stabiliser deflection, which in theory could be overcome by manual nose-up input from the pilots. However, Boeing's SOP, which recommended deactivating the MCAS, did not explain that such a procedure just reset it rather than disabled it. If the same faulty AOA input recurred MCAS would then deflect the stabiliser up to 2.5 degrees. But here's the fatal flaw: it had no "memory" of previous deflections after each reset, and it had no provision for checking the current deflection, so each activation of MCAS ADDED ANOTHER 2.5 DEGREES of nose-down!!
That explains why both Lion Air and EA appeared to porpoise - manually regaining climb after the first deactivation but increasingly unable to do so as the jackscrew added each incremental 2.5 degrees of MCAS-commanded nose-down to its existing setting until the horizontal stabiliser was beyond the pilots' ability to counter with elevator nose-up commands. What is shocking is both the flaw in the software and Boeing's deliberate decision to withhold full information about MCAS so that they could market MAX as a no-conversion option for existing B738 pilots. As is now apparent, no B738 simulator incorporated MCAS and no pilot was aware how to fully disable MCAS to avoid it continually re-activating, assuming they would even appreciate the need to do so given the limits of the SOP Boeing had provided. If my theory is confirmed by the investigation team Boeing's civil liability may be the least of its problems ...
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Philip Last edited by Philip Argy; 5th April 2019 at 12:21 PM. Reason: Correct typos |
#33
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EA preliminary report just released
http://www.ecaa.gov.et/documents/204...8-d7af1ee17f3e
The key finding from the FDR, is that this occurred AFTER the electric stabiliser trim cutout switches had been pulled: Quote:
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Philip Last edited by Philip Argy; 5th April 2019 at 03:25 PM. Reason: Added key findings |
#34
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Quote:
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Happy to stand corrected, but the way I understand it was that they were unable to exert enough force on the manual trim wheel (due to the airspeed) and reactivated the trim cutout switches.
Quote:
Quote:
Then; Quote:
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#36
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Interesting comment on the investigations to date:
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#37
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Pilot error claim objectively unfair
The fact is that Boeing promoted the MAX as requiring little to no conversion training from a 737-800 - an hour on an iPad was one quote I saw. In that context any inability of crew to cope with differences with which they were not familiar, and which had never been incorporated into any simulator, cannot be the principal cause of either event. Pilot error based on informed hindsight has no place here.
Having said that, yes, I have speculated more than I should have about the role of MCAS, but the inferences are there to be drawn.
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Philip |
#38
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Looks like Boeing have decided to put the accidents back on the pilots:
Boeing CEO Points at pilot error |
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Primitive inputs need more redundancy and resilience
However sophisticated the avionics, the old adage of garbage in garbage out applies. Primitive physical sources like pitot tubes and AofA sensors need redundancy and resilience before they are taken as trusted sources for sophisticated avionics. Taking a single sensor as a trusted source was objectively poor risk management in the implementation of MCAS.
There have been too many examples of erroneous data from pitot tubes and AofA sensors causing adverse avionics responses. This needs much more focus going forward IMHO. Blaming pilots is hardly helpful - human error needs to be anticipated in system design. It's no use if the cure is worse than the complaint. Pilots know what to do when the stick shakes. MCAS is not necessarily the best solution to the MAX propensity to stall!
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Philip |
#40
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As I was saying ...
How dare they blame the pilots!
Now this: https://airlinerwatch.com/boeing-nev...sources-claim/ My case rests ...
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Philip |
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