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Old 10-20-2019, 09:38 PM   #11
captaincog
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From what I have read the biggest issue with this aircraft is too big engines and the placement of them created an aircraft that has a larger potential to stall so the control system was meant to overcome this since there was a huge cost savings in keeping the current airframe. But, like a front engine Corvette, there has to be a significant amount of engineering with software and control systems to make them operate as a normal driver or pilot is accustomed to...….the system flaw of an overriding nosedive was not expected to result in crashes.
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Old 10-21-2019, 09:39 AM   #12
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Well, I think that's an oversimplification of the issues. However, suffice to say that the different engines and placement does change the handling characteristics of the airplane. This is hardly the first aircraft that has had an automated system kick in and cause a crash, just the latest example.
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Old 10-21-2019, 03:40 PM   #13
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Larger nacelles on the MAX placed the front of the engine more forward than in previous 737s. This resulted in a tendency for the nose to pitch up more than previous models. In order for the plane to behave more like its predecessor the 737NG, they installed the MCAS system, which would respond to extreme pitch angles by pushing the nose down. However, the system had issues that were either known and not dealt with, or unknown until the plane was in service. I'm not going to speculate on which of those occurred.
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Old 10-21-2019, 08:29 PM   #14
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One issue was only one angle of attack sensor, if that fails, the MCAS system may have a problem knowing what to do. Apparently, one of the fixes is to install two angle of attack sensors and do comparisons. If they don't agree, they'll automatically turn off the MCAS to avoid false maneuvering cues. Also, they are enhancing the ability of the pilot to simply override the automatic controls with yoke inputs, apparently the first generation was a bit too aggressive.
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Old 10-22-2019, 03:02 PM   #15
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One issue was only one angle of attack sensor, if that fails, the MCAS system may have a problem knowing what to do. Apparently, one of the fixes is to install two angle of attack sensors and do comparisons. If they don't agree, they'll automatically turn off the MCAS to avoid false maneuvering cues.
I read that. Seems interesting that they only had one to begin with. Redundancy is built-in to most flight controls, why not this one?

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Also, they are enhancing the ability of the pilot to simply override the automatic controls with yoke inputs, apparently the first generation was a bit too aggressive.
Turning off MCAS was apparently not straightforward. And the training required to fully understand the system was not well implemented.
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Old 10-22-2019, 04:38 PM   #16
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One issue was only one angle of attack sensor, if that fails, the MCAS system may have a problem knowing what to do. Apparently, one of the fixes is to install two angle of attack sensors and do comparisons. If they don't agree, they'll automatically turn off the MCAS to avoid false maneuvering cues.
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I read that. Seems interesting that they only had one to begin with. Redundancy is built-in to most flight controls, why not this one?
Hard to say, those are mechanical devices that have failed in the past, I believe at least one accident has been blamed on one failing. That's besides this pair of accidents.

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Also, they are enhancing the ability of the pilot to simply override the automatic controls with yoke inputs, apparently the first generation was a bit too aggressive.
Quote:
Turning off MCAS was apparently not straightforward. And the training required to fully understand the system was not well implemented.
Actually, there was no training on the MCAS, they were trying to "keep it simple". They were assuming that the automated system would only kick in when needed. Probably not the smartest decision that was ever made.
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Old 10-22-2019, 08:11 PM   #17
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Wikipedia is not normally my first source of information regarding aviation matters, but information seems to be scarce on exactly how this system operates and on what dependancies and what depends on the system.

Whomever wrote this page appears to know what he's talking about, or at least has the appearance of that.

This gave me a better understanding of how this system operates. Heck, the Boeing Pilots Operating Manual doesn't even describe this system.

In the old days, IE, the Boeing 727-200 and 737-200, the Sperry SP-50 and SP-150 was set up so that if there was input to the control column or yoke, the A/P would completely disengage. There were also Stab Cutout switches on the throttle housing that would control a runaway stab trim condition in case of screw jack failure or switch failure.

It was a simple but effective system that worked. It's too bad that computerized flight control systems have mucked up the simplest things.

They could have retained the original engine position by simply building the landing gear taller and moving it farther outboard, or as with the CFM65 engine fan shroud, flatten it at the bottom and not raise the gear so much.

Instead of aerodynamically fixing this error, they try to band-aid it with computer software. It's not a B-2.

https://en.wikipedia.org/wiki/Maneuv...ntation_System
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Old 10-22-2019, 08:45 PM   #18
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I resorted to Wikipedia because there was no other reasonable source of information on the system. Like you say, it at least appeared that the guy that wrote that had some knowledge of the specific systems and aircraft.

The problem with making the landing gear taller would have been a major modification of the fuselage, that would have been costly I suspect. Then there's the issue with mating up with jetways, they have a limited amount of up/down travel.

I'm sure the engine placement was the cheapest way to fit the new engines to the airframe.

The biggest mystery, at least to me, is why they depended on a single AOA sensor for such a flight critical function. It's also somewhat of a mystery how it passed the scrutiny of the FAA, I sure never got anything that brazen past them!

You can bet your bippie that the future holds more FAA scrutiny of Boeing until they clean up their act!
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Old 10-22-2019, 08:57 PM   #19
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I agree. On the aircraft I mentioned there was an instrument comparitor mounted above the ADI that compared the various inputs from the flight data computer. If something didn't agree within so many degrees, knots, feet, and so on, one of the comparitor lights would illuminate alerting you to what the problem could be and where to look for it.

How could Boeing not build in a comparitor that used both AOA sensors is beyond me and beyond stupid.

Now they 'get it' though. Duh.
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Old 10-23-2019, 09:17 AM   #20
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Aviation is riddled with this kind of issue, someone overlooks some aspect of safety or reliability, and it comes back to bite them, sometimes many years later.
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