Boeing Max.

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boeingboy
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Re: Boeing Max.

Post by boeingboy »

MCAS was in the Max since the beginning. It's primary purpose was - and still is - load alleviation

It wasn't until late in flight testing that the plane was found to have this problem of the nose staying up at high angles of attack and low speed - so the easy thing to do was add a stick pusher subsystem into the MCAS software.

Load alleviation and stick pushers have been in aircraft for decades.
Where they went wrong was only tying it to one AOA sensor.
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digits_
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Re: Boeing Max.

Post by digits_ »

boeingboy wrote: Thu Aug 29, 2019 11:25 am MCAS was in the Max since the beginning. It's primary purpose was - and still is - load alleviation

It wasn't until late in flight testing that the plane was found to have this problem of the nose staying up at high angles of attack and low speed - so the easy thing to do was add a stick pusher subsystem into the MCAS software.

Load alleviation and stick pushers have been in aircraft for decades.
Where they went wrong was only tying it to one AOA sensor.
And giving it too much authority, too much of a nose down moment when it activated.
But it needed that amount of authority to properly recover... Yet it moved too much to get certified, but needed to move that much to be certified. oh-oh...
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Re: Boeing Max.

Post by photofly »

The on-again off-again aspect of MCAS seems unusual. Stick pushers, stick feel adjustment systems, load alleviation systems - isn't it unusual for them to run for 5 seconds, then shut down for 10 seconds, then magically start up again? Wouldn't they be either active at a given point in the flight envelope or inactive? Anyone know?
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C.W.E.
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Re: Boeing Max.

Post by C.W.E. »

How many airline category airplanes require a computer driven ( load alleviation ) device to stop a pitch excursion caused by the engine thrust needed to take off and climb that is so powerful it can cause the airplane to crash if it is handled improperly?
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imcool
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Re: Boeing Max.

Post by imcool »

https://www.bloomberg.com/news/articles ... -engineers

This also make me nervous. More I read about malpractices more I get nervous for this Max plane.
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Re: Boeing Max.

Post by C.W.E. »

“Boeing has many decades of experience working with supplier/partners around the world,” a company spokesman said. “Our primary focus is on always ensuring that our products and services are safe, of the highest quality and comply with all applicable regulations.”
Ahhhh, now I feel better about this Boeing Max issue.

It is not Boeing that is responsible for these crashes it is the pilots just were not capable of figuring out what it was doing and sort of got a little behind what it was doing.
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GoinVertical
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Re: Boeing Max.

Post by GoinVertical »

C.W.E. wrote: Thu Aug 29, 2019 12:24 pm How many airline category airplanes require a computer driven ( load alleviation ) device to stop a pitch excursion caused by the engine thrust needed to take off and climb that is so powerful it can cause the airplane to crash if it is handled improperly?
How many transport category aircraft have any form of automation that effects primary flight controls without redundant input? Stick pusher that takes data from only one source? Even the stab trim switches need redundant input to function.

Whoever designed the MCAS system to take information from only on AOA sensor and not compare to the other should be taken out behind the barn, as far as I'm concerned.

Oh, and then let's not tell pilots that the system exists, let alone how poorly it's designed.
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imcool
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Re: Boeing Max.

Post by imcool »

GoinVertical wrote: Thu Aug 29, 2019 2:06 pm
C.W.E. wrote: Thu Aug 29, 2019 12:24 pm How many airline category airplanes require a computer driven ( load alleviation ) device to stop a pitch excursion caused by the engine thrust needed to take off and climb that is so powerful it can cause the airplane to crash if it is handled improperly?
How many transport category aircraft have any form of automation that effects primary flight controls without redundant input? Stick pusher that takes data from only one source? Even the stab trim switches need redundant input to function.

Whoever designed the MCAS system to take information from only on AOA sensor and not compare to the other should be taken out behind the barn, as far as I'm concerned.

Oh, and then let's not tell pilots that the system exists, let alone how poorly it's designed.
that too programmed by 9$ per hour programmers to save the cost :/
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boeingboy
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Re: Boeing Max.

Post by boeingboy »

How many airline category airplanes require a computer driven ( load alleviation ) device to stop a pitch excursion caused by the engine thrust needed to take off and climb that is so powerful it can cause the airplane to crash if it is handled improperly?
There is so much wrong with this statement - it makes me wonder if you understand anything of the actual problem
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boeingboy
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Re: Boeing Max.

Post by boeingboy »

The on-again off-again aspect of MCAS seems unusual. Stick pushers, stick feel adjustment systems, load alleviation systems - isn't it unusual for them to run for 5 seconds, then shut down for 10 seconds, then magically start up again? Wouldn't they be either active at a given point in the flight envelope or inactive? Anyone know?
Generally speaking - A stick pusher/stall warning will remain active until the stall has been counteracted. In the case of the max - As it only had one AOA input and the vane was damaged by a bird (Ethiopian) the AOA told the plane he was at 74 degrees nose up. The system operated as designed, except that the AOA input to the computer never changed so the plane thought it was still stalled.

The on again off again that you refer to is due to the fact that Boeing - in addition to being able to turn it off altogether - basically said if the pilot wants to over ride the system - he can with the electric pitch trim, which is what the pilots of both flights were doing. Although I still cant figure for the life of me why they just didn't trim the plane back to level flight. Theywould only trim for 2 or 3 seconds after the system trimmed for much longer than that
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Eric Janson
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Re: Boeing Max.

Post by Eric Janson »

boeingboy wrote: Thu Aug 29, 2019 8:25 pm Although I still cant figure for the life of me why they just didn't trim the plane back to level flight. They would only trim for 2 or 3 seconds after the system trimmed for much longer than that.
This is one possible explanation:-

It's apparent that both crews had to apply increasing force on the yoke in an effort to maintain level flight. If you really need to exert maximum force on the yoke then your hands will need to move down slightly from their normal position. That is just enough to make accessing the trim switches difficult.
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FICU
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Re: Boeing Max.

Post by FICU »

The Ethiopian Captain used control wheel force to bring the nose up rather than the nicely placed electric trim switches by his thumb. He forgot about controlling the thrust and then he got tired. In the Lion Air crash the pilot used the electric trim switches many, many times to bring the nose up and it worked it would seem until he handed control over to search the checklists.
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Re: Boeing Max.

Post by fish4life »

The craziest part is the Ethiopian crew had it fixed but instead of manually trimming the airplane after turning off the electric trim they turned it back on causing the MCAS to run again.
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mijbil
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Re: Boeing Max.

Post by mijbil »

Hey F4L, From reading the initial crash investigation report I think that they did try to trim it manually but the force from the CA hauling back on the elevators to try and counteract the Aircraft Nose Down commanded by the stab was too much for the manual trim wheel to overcome. The analogy I was told was that it's like having a really big fish on a line that you can't reel in (trim manually) The only way to trim manually is to release back pressure momentarily, trim like mad manually, haul back on the yoke again and repeat as necessary. It's similar to lowering the rod tip while reeling in the fishing line and then hauling up the rod again.
Here is a brief excerpt from the Ethiopian crash report : At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working."
And from the Boeing FCTM : Excessive air loads on the stabilizer may require effort by both pilots to correct the mis-trim. In extreme cases, it may be necessary to aerodynamically relieve the airloads to allow manual trimming. Accelerate or decelerate towards the in-trim speed while attempting to trim manually.
What isn't mentioned is that you might need a fair bit of altitude to relieve that airload.
The link posted by Flying Low written by an engineer is the best explanation so far that I have seen of the MCAS system.
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boeingboy
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Re: Boeing Max.

Post by boeingboy »

The link posted by Flying Low written by an engineer is the best explanation so far that I have seen of the MCAS system.
Oh please - it's his own opinion and works for Airbus.....half of what he states is a crock.
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Re: Boeing Max.

Post by Flying Low »

Oh please - it's his own opinion and works for Airbus.....half of what he states is a crock.
Fair enough. Now what is incorrect in the article?
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Re: Boeing Max.

Post by DH82EH »

boeingboy wrote: Thu Aug 29, 2019 8:10 pm
How many airline category airplanes require a computer driven ( load alleviation ) device to stop a pitch excursion caused by the engine thrust needed to take off and climb that is so powerful it can cause the airplane to crash if it is handled improperly?
There is so much wrong with this statement - it makes me wonder if you understand anything of the actual problem
The answer is simple. One, although it is not currently in service.
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Re: Boeing Max.

Post by lostaviator »

Once you get yourself into the situation of having that much nose down trim, at such a low altitude, you are done.

The manual trim wheel won’t move with the opposing forces applied. The only way to trim is to release all force and let the nose fall. If you don’t have a few thousand feet, it’s all over.
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Re: Boeing Max.

Post by pilotbzh »

lostaviator wrote: Wed Sep 04, 2019 3:45 pm Once you get yourself into the situation of having that much nose down trim, at such a low altitude, you are done.

The manual trim wheel won’t move with the opposing forces applied. The only way to trim is to release all force and let the nose fall. If you don’t have a few thousand feet, it’s all over.
Not true, first pull hard to bring the nose up respecting the stall warning, then release pressure to manually trim nose up, no need to loose altitude.... as long as you control the speed, it won't work if you let the speed go 350+Kts
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Re: Boeing Max.

Post by GoinVertical »

pilotbzh wrote: Wed Sep 04, 2019 4:09 pm
lostaviator wrote: Wed Sep 04, 2019 3:45 pm Once you get yourself into the situation of having that much nose down trim, at such a low altitude, you are done.

The manual trim wheel won’t move with the opposing forces applied. The only way to trim is to release all force and let the nose fall. If you don’t have a few thousand feet, it’s all over.
Not true, first pull hard to bring the nose up respecting the stall warning, then release pressure to manually trim nose up, no need to loose altitude.... as long as you control the speed, it won't work if you let the speed go 350+Kts
What if the stab is trimmed so nose - down that full up elevator only gives you level flight or just slightly better?
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