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ludi
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Re: DYMT: Imi's Legacy

Wed Apr 03, 2019 10:07 pm

Yeah, it's still not clear on why the system was turned on again. The pilots were under severe stress at that point and may have reactivated it by intent or mistake. Once a system stops behaving as expected, the risk of user error goes way up.
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 8:27 am

You can't actually turn off MCAS. MCAS is just one of a number of systems that feed trim commands to the horizontal stabiliser (tail plane). What you actually do is you turn off the power to the trim motors. There are 2 switches to turn off the trim motors, one for autopilot and one for manual. MCAS actually goes through the manual trim path. Normally the pilot trims by pushing buttons on the control column. If you turn off the manual trim you now have to trim the aircraft by winding the trim wheel round and round by hand.

If the trim is very nose down and you are pulling back on the control column to keep the plane level and the plane is flying fast enough then you may not be able to actually move that wheel by hand, the aerodynamic forces on it will be jamming it. There is a technique where you have to get the nose high with both pilots pulling on the control columns together (60lbs of pull force) and then you let the nose drop. As the nose drops then the aerodynamic load comes off the horizontal stabiliser and you can now wind a few turns of nose up trim on before you need to do the both pulling together to stop it nose diving in to the ground. I've read reports of pilots doing it in a simulator and they said it's a real rollercoaster ride. It's not something that's part of the standard simulator training, they had completed all their standard simulator training and were trying some "what if..." type things, so most pilots wouldn't normally be thinking of this.

The Ethiopian flight was actually flying very fast - they had normal takeoff and climb power set but were not actually climbing so all that power went in to the aircraft speed. They may have decided to turn the manual trim back on to get the motors to help trim the nose back up, but this then let the MCAS drive the trim nose down again and kill them.

One of the other things that I haven't seen reported on but I have seen pilots chat about, is what this would look like in the cockpit with one of the Angle of Attack sensors reading high. As soon as the wheels came off the ground, the aircraft would see the high AoA on one side and that would set the stick shaker rattling and trigger stall warnings. The cockpit would go from a normal takeoff roll to a cacophony of sound telling you that you are stalling. Without an AoA disagree warning light (optional) and a screen menu to compare AoA readings (optional), the only symptom that this is a false warning triggered by a sensor failure is that the stick shaker is only shaking on the side with the failed sensor - the other control column isn't shaking. At this point MCAS isn't active - it only comes in once the flaps are up. The response to a stall warning is to lower the Angle of Attack (i.e. nose down, but if you have the ground right there you are going to crash) and increase speed. As the speed increases you need to bring the flaps up - they have a max speed before they get ripped off the wing, and when you do that then the MCAS kicks in and tries to kill you. You can use the trim buttons to trim it nose up which stops MCAS for a few seconds - making you think that you don't have runaway trim, but after a little while it starts trimming nose down again. Also because you are now travelling fast, you have that large aerodynamic load on the trim. It's a nasty place to be.
 
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 8:34 am

IOW it looks like we may have a situation where incredibly bad UI design has literally killed hundreds of people.
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 8:56 am

just brew it! wrote:
IOW it looks like we may have a situation where incredibly bad UI design has literally killed hundreds of people.

Apparently because Boeing and the airlines didn't want to retrain 737 NG pilots on the MAX 8/9 by claiming that there were no differences in their flight characteristics and/or control laws.
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 12:33 pm

Preliminary report just released - PDF here:
http://www.ecaa.gov.et/documents/20435/ ... af1ee17f3e
 
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 12:33 pm

I'm more baffled that they didn't rely on the AoA Disagree condition to limit or disable MCAS from the beginning. What is the logic in not using redundant inputs when you already have them?
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 12:44 pm

ludi wrote:
I'm more baffled that they didn't rely on the AoA Disagree condition to limit or disable MCAS from the beginning. What is the logic in not using redundant inputs when you already have them?

Boeing was selling the Disagree notification as an extra-cost upgrade (IIRC from reading somewhere, $50K/plane) and low-cost airlines didn't buy. From Page 28 of the PDF, from the Boeing Flight Manual (runaway trim instructions):

AOA DISAGREE ALERT (If the option is installed)
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Re: DYMT: Imi's Legacy

Thu Apr 04, 2019 1:02 pm

Captain Ned wrote:
ludi wrote:
I'm more baffled that they didn't rely on the AoA Disagree condition to limit or disable MCAS from the beginning. What is the logic in not using redundant inputs when you already have them?

Boeing was selling the Disagree notification as an extra-cost upgrade (IIRC from reading somewhere, $50K/plane) and low-cost airlines didn't buy. From Page 28 of the PDF, from the Boeing Flight Manual (runaway trim instructions):

AOA DISAGREE ALERT (If the option is installed)

Right. But if both inputs were available anyway (as appears to have been the case), they should've been used internally by the MCAS system as a double-check even if the sensor fault wasn't explicitly displayed as a notification to the pilots. I think Boeing may have opened themselves up to some serious liability here by not doing something obvious which would've cost them almost nothing and would've made the system significantly safer.
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Re: DYMT: Imi's Legacy

Fri Apr 05, 2019 5:13 pm

Catch of the day: a small office in the next building over is liquidating, and sent around flyers advertising walk-ins welcome. Picked up a trio of Dell U2414Hb monitors (23.8" bezzel-less IPS, 1080P) for $25 each.
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Re: DYMT: Imi's Legacy

Fri Apr 05, 2019 5:15 pm

Nice, I think I had some of those before I joined the 21:9 club. I paid a lot more than $25 a piece though. :lol:
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Re: DYMT: Imi's Legacy

Sun Apr 07, 2019 9:53 pm

Dreading going in to the office tomorrow. Last week can be summed up by this GIF, and I expect it to continue.

On the home front, I just discovered that the new TV we bought is about an inch too wide for the entertainment center. Shouldn't have trusted my wife and son to make sure it would fit... :roll:
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 6:35 am

just brew it! wrote:
On the home front, I just discovered that the new TV we bought is about an inch too wide for the entertainment center. Shouldn't have trusted my wife and son to make sure it would fit... :roll:

People still use Entertainment centers?
 
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 8:22 am

Usacomp2k3 wrote:
just brew it! wrote:
On the home front, I just discovered that the new TV we bought is about an inch too wide for the entertainment center. Shouldn't have trusted my wife and son to make sure it would fit... :roll:

People still use Entertainment centers?

You know how heavy those things are, right? If you got one for a good-sized CRT back in the 90s or early 00s, it's just part of the house now!
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 8:48 am

superjawes wrote:
You know how heavy those things are, right? If you got one for a good-sized CRT back in the 90s or early 00s, it's just part of the house now!

The last time we moved, the entertainment center stayed for just that reason. It was so heavy. We replaced it with an all metal-and-glass Z-shaped frame stand that weighs 1/3 as much and takes up far less space, too.
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 10:01 am

just brew it! wrote:
Dreading going in to the office tomorrow. Last week can be summed up by this GIF, and I expect it to continue.


What is going on that is so exciting?
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 10:05 am

And many/most people wall-mount the TV (Myself included) that they aren't needed for that purpose. We have a drawer unit under the TV in the living room, but that is for shoes and other "mudroom" type objects. The AppleTV sits on top of the TV and nothing else connects to it.
 
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 10:36 pm

MileageMayVary wrote:
just brew it! wrote:
Dreading going in to the office tomorrow. Last week can be summed up by this GIF, and I expect it to continue.

What is going on that is so exciting?

People freaking out over deadlines and broken stuff. Other people getting cranky because people are freaking out. Today could've been worse, but I'm just now calling it a night since there's not much more I can do about my piece of the freak-out until I see the results of the code reviews and regression tests.

Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.
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Re: DYMT: Imi's Legacy

Mon Apr 08, 2019 11:45 pm

just brew it! wrote:
Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.

Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 6:40 am

ludi wrote:
just brew it! wrote:
Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.

Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.

This plan definitely would not be wife-approved!
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 7:50 am

just brew it! wrote:
ludi wrote:
just brew it! wrote:
Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.

Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.

This plan definitely would not be wife-approved!

Even if she gets to do the shopping?
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 8:32 am

just brew it! wrote:
ludi wrote:
Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.

This plan definitely would not be wife-approved!

At least the suggestion didn't include cinder blocks :lol:
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 10:00 am

Usacomp2k3 wrote:
And many/most people wall-mount the TV (Myself included) that they aren't needed for that purpose. We have a drawer unit under the TV in the living room, but that is for shoes and other "mudroom" type objects. The AppleTV sits on top of the TV and nothing else connects to it.

Many maybe, but definitely not most. Of all the houses I've been in, I can think of only one other besides mine that uses a VESA mount of any kind. Both of those mounts (one of them being mine) are built into stand. I thought about a wall mount for the office TV, but it's awfully permanent. Filling holes and repainting is a pain.
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 10:01 am

Heiwashin wrote:
just brew it! wrote:
This plan definitely would not be wife-approved!

Even if she gets to do the shopping?

Probably not. She picked out the current one. When it comes to stuff like this she seems to have a "go big or go home" mindset...

superjawes wrote:
At least the suggestion didn't include cinder blocks :lol:

That actually occurred to me as a potential temporary stopgap! :lol: (And no, that wouldn't have been wife-approved either, even as a temporary measure.)

When I was in college, my "entertainment center" literally WAS a wooden door laid across stacks of cinder blocks.
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 10:04 am

ludi wrote:
just brew it! wrote:
Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.

Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.



Step 1: Wait for wife to go somewhere for a couple hours
Step 2: Hack away at entertainment center with a hatchet in a completely random manner
Step 3: Stage a scene using 2-3 stuffed animal beavers and fake blood/ketchup
Step 4: Call wife in a panic, telling her "Beavers got into the house, and they're tearing apart the entertainment center!" complete with banging and chainsaw sounds in the background
Step 5: End call abruptly, don't answer the phone for a couple minutes, and then text photographic evidence of the "dead" beaver scene
Step 6: Call your wife back and tell her "I got the beavers, but not before they did a number on the entertainment center"
Step 7: Conveniently clean up the "gore" before she arrives home
 
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 10:51 am

The Egg wrote:
Step 1: Wait for wife to go somewhere for a couple hours
Step 2: Hack away at entertainment center with a hatchet in a completely random manner
Step 3: Stage a scene using 2-3 stuffed animal beavers and fake blood/ketchup
Step 4: Call wife in a panic, telling her "Beavers got into the house, and they're tearing apart the entertainment center!" complete with banging and chainsaw sounds in the background
Step 5: End call abruptly, don't answer the phone for a couple minutes, and then text photographic evidence of the "dead" beaver scene
Step 6: Call your wife back and tell her "I got the beavers, but not before they did a number on the entertainment center"
Step 7: Conveniently clean up the "gore" before she arrives home

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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 11:34 am

Humans sleep soundly in their beds because rough cats stand ready in the night to visit violence on those who would do us harm.
 
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 11:50 am

Captain Ned wrote:

Leslie Neilsen's delivery makes that whole series. :lol:
 
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 3:08 pm

The Egg wrote:
ludi wrote:
just brew it! wrote:
Re entertainment center: Need to spread out the side towers a few inches, lengthen the center shelf that runs between the towers, get a TV stand that can attach to the new TV's VESA mount holes because the legs that came with the TV are too far apart for the existing platform, and replace all of the cables with longer ones.

Step 1: Blow up existing entertainment center.
Step 2: Monoprice wall mount for TV.
Step 3: For everything else, there's IKEA.



Step 1: Wait for wife to go somewhere for a couple hours
Step 2: Hack away at entertainment center with a hatchet in a completely random manner
Step 3: Stage a scene using 2-3 stuffed animal beavers and fake blood/ketchup
Step 4: Call wife in a panic, telling her "Beavers got into the house, and they're tearing apart the entertainment center!" complete with banging and chainsaw sounds in the background
Step 5: End call abruptly, don't answer the phone for a couple minutes, and then text photographic evidence of the "dead" beaver scene
Step 6: Call your wife back and tell her "I got the beavers, but not before they did a number on the entertainment center"
Step 7: Conveniently clean up the "gore" before she arrives home

My dad did something like steps 1 and 2, but he used a chainsaw to cut out a portion of the left side. Now the 37" 16:9 TV fits in the space originally created for a 35" CRT with 4:3 aspect ratio. And considering how much he paid for it back in the 1990s, my mom was somehow OK with being able to continue using it.
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 4:06 pm

derFunkenstein wrote:
My dad did something like steps 1 and 2, but he used a chainsaw


That's a boss move. There aren't many ways in which house+chainsaw ranks high on the WAF.
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Re: DYMT: Imi's Legacy

Tue Apr 09, 2019 11:08 pm

Redocbew wrote:
derFunkenstein wrote:
My dad did something like steps 1 and 2, but he used a chainsaw


That's a boss move. There aren't many ways in which house+chainsaw ranks high on the WAF.

My parents are way more badass than I will ever be, sadly.
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