Ethiopian airliner down in Africa

[KRUSTY 34]

Originally Posted by ktcanuck

When all is said and done, the one common indicator is the AoA reading on the Cap's side. Debate everything else till your heart's content.

Why did it flip to ~75deg at 150kn? More interestingly, why did it flip back to "normal" for a moment just before end of flight before flipping back to error?

I assume the slowly diverging altitude readings relate to the AoA stuck at 75 while pitot static reads ok...

Boeing's proposed fix includes shutting off the "required" MCAS when AoA disagrees so this is kind of important.

Whisky Tango Foxtrot guys? What's happening to that vane or the electrons/code behind it?

WTF indeed. So when a critical data input sensor fails, take the system out of the picture. A system that was vital to the certification of the aircraft.

I think you’ll have to do better than that guys!

[FrequentSLF]

I have not seen any comment regarding the force required to crank manually the trim wheels, those are mechanically connected to the stabilizer therefore to change stabilizer position rotating manually the wheels will require to overcame the load on the stabilizer. It is stupid to think that the forces on stabilizer at those speeds made hard if not impossible to manually change stabilizer position?

[George Glass]

05:38:45 Lefthand stick shaker sounds
05:39:00. Captain attempts to engage LH Autopilot.....................

[KRUSTY 34]

Originally Posted by FrequentSLF

I have not seen any comment regarding the force required to crank manually the trim wheels, those are mechanically connected to the stabilizer therefore to change stabilizer position rotating manually the wheels will require to overcame the load on the stabilizer. It is stupid to think that the forces on stabilizer at those speeds made hard if not impossible to manually change stabilizer position?

Are you sure about that?

[RickNRoll]

Originally Posted by KRUSTY 34

WTF indeed. So when a critical data input sensor fails, take the system out of the picture. A system that was vital to the certification of the aircraft.

I think you’ll have to do better than that guys!

When AF447 had the pitot tubes freeze up it dropped the plane back into manual flight mode and alternate law. That is OK if you are trained for it and respond accordingly. There was no simulator training for the MAX if the MCAS failed, even if you had the MAX simulator and Boeing said no one needed any simulator time for the MAX.

[OldnGrounded]

Originally Posted by FrequentSLF I have not seen any comment regarding the force required to crank manually the trim wheels, those are mechanically connected to the stabilizer therefore to change stabilizer position rotating manually the wheels will require to overcame the load on the stabilizer. It is stupid to think that the forces on stabilizer at those speeds made hard if not impossible to manually change stabilizer position?

Originally Posted by KRUSTY 34

Are you sure about that?

I'm pretty sure we have some confusion here based upon misunderstanding of a post by a non-native writer of English.

FrequentSLF: There have been a number of posts here, and coverage in the news media, addressing the issue of difficulty operating the manual trim wheels under high loads. It's pretty much agreed that it would be very hard. Your post seems to say that you believe that isn't true, but I don't think that's what you meant. Can you help us?

[FrequentSLF]

Originally Posted by OldnGrounded

Originally Posted by FrequentSLF I have not seen any comment regarding the force required to crank manually the trim wheels, those are mechanically connected to the stabilizer therefore to change stabilizer position rotating manually the wheels will require to overcame the load on the stabilizer. It is stupid to think that the forces on stabilizer at those speeds made hard if not impossible to manually change stabilizer position?

I'm pretty sure we have some confusion here based upon misunderstanding of a post by a non-native writer of English.

FrequentSLF: There have been a number of posts here, and coverage in the news media, addressing the issue of difficulty operating the manual trim wheels under high loads. It's pretty much agreed that it would be very hard. Your post seems to say that you believe that isn't true, but I don't think that's what you meant. Can you help us?

thanks, yes i meant that would be pretty hard to operate the manual,trim under high loads, sorry for the confusion i might have created

[jimjim1]

Originally Posted by Loose rivets

Gulp. Murphy, you're erm . . . right. Not like me to fuzzle mechanical things. Must stop posting at 02 sparrows. :-(

Here is something more to fuzzle with

Miraculously I have found the diagram of an AoA sensor that I remembered seeing. It is from a 747 I think it says and has dual encoders but the ideas are all the same.

https://www.satcom.guru/2019/03/aoa-...-fix.html#more

[NSEU]

Originally Posted by FrequentSLF

I have not seen any comment regarding the force required to crank manually the trim wheels,....

The Maintenance Manual has upper and lower limits when there are no airloads:

The torque required to turn the wheel is somewhere between 22 and 62pound-inches (2.5 and 7 newton-meters).

What's the radius of the trim wheel at the handle position?

[YRP]

- After autopilot engagement, there were small amplitude roll oscillations accompanied by lateral acceleration, rudder oscillations and slight heading changes; these oscillations also continued after the autopilot disengaged.

So what is the significance or cause of this item in the report? Is this the result of the AoA sensor issue leading to the autopilot trying to track spurious inputs?

Or is it an unrelated problem, something else wrong?

[NSEU]

Originally Posted by Loose rivets

I just can't get to grips with the concept of a weight. Counter-balance or not. My recollection of checking the vanes was that they stayed put to wherever you shoved them. Having any weight would make them subject to accelerative forces - the weight of the vane itself would be almost totally air-supported and while still affected by g, it would be minuscule compared to the pressure of the air.

Wouldn't the accelerative forces apply to the vane and the counter balance about the pivot point? So possibly no rotation due to equal forces up/down around the pivot point. I also recall the vanes stay roughly where you put them. They feel fluid-damped.

[FGD135]

Not difficult to rotate the trim wheels under certain circumstances, but impossible.

IMPOSSIBLE.

Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).

The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.

IMPOSSIBLE.

[fotoguzzi]

[Not a pilot] I note that they had time to communicate and navigate. They set altitudes and headings and communicated their intentions.

Back pressure increases, but that is not graphed, so we will have to wait eighteen months to learn how much they were exerting while they were setting altitudes, headings, etc.

Within five seconds the Captain went from climbing to 32,000 ft to requesting to maintain runway heading. Are the voice and data timestamps compatible?

Summary with points of interest:
takeoff trim 5.6
man/elec trim 4.9 to 5.9 end 5.6
trim via ?? Down from 5.6 to 4.6
auto trim Down from 4.60 to 2.1
man/elec trim Up from 2.1 to 2.4
auto trim Down from 2.4 to 0.4

"At 05:40:28 Manual electric trim in the ANU direction was recorded and the stabilizer reversed moving in the ANU direction and then the trim reached 2.3 units." [One of these ANUs is a typo, no?]

man/elec trim Up 0.4 to 2.3
Cutout

"From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units." [Approximately, 0.1 units / min.]

"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. At 05:43:04, the Captain asked the First Officer to pitch up together and said that pitch is not enough."

A minute into the two and a half minutes of nose down trim, the Captain asks a reasonable question. Within a span of eight seconds the FO answers that trim is not working, oddly suggests trying manual, gets permission, and says, Nope. What exactly was the Captain asking? What did the FO mean by manual? The nose down was gradual, but the FO only worked on whatever "manual" was for eight seconds.

They worked together on something for seven seconds. Did each have a yoke in one hand and a hand wheel in the other? So, fifteen seconds of trying did not defeat the gradual nose down of 0.2 units in two and a half minutes. Or, another interpretation: eight seconds of cranking in the wrong direction didn't seem to be helping. This interpretation is at odds with the stated "gradual" nose down.

trim Down via ?? from 2.3 to 2.1
Normal [Inferred]
manu/elec trim Up from 2.1 to 2.3
auto trim Down 2.3 to 1.0
trim via ?? 1.1 to 0.8

[GlobalNav]

Originally Posted by dingy737

Question:
Why did Boeing give a FULL description of the NG’s , STS, in their FCOM but ONLY mention MCAS in the abbreviation section of the MAX FCOM.
A. Because a full description would highlight an unwanted flight characteristic forced onto a 1967 airframe, pushing it beyond the MAX. ( criminal)
B. It was considered better to cover up & hide this aerodynamic instability, which could open Pandora’s box and affect market $hare against the NEO. ( criminal)
C. Because their partner in crime the FAA, allowed them. ( criminal)
D. Because they thought their magic software would magically make their shoe horned design failure disappear.
E. All of the above.

The answer is always “ all of the above”.

I won't pretend to know the answer, but suggest one other possibility, supported by previous posts. Boeing needed to minimize the training load, as a selling point and commitment to its airline customers. The more that goes into the FCOM that is unique to the Max, the more pilot training must address it. It would seem that when assessing the need for FCOM documentation and training, Boeing (and FAA?) focused on how MCAS works when fully operational (no malfunctions), requiring no pilot response. Its function is to make the handling of the Max in pitch at high AoA so similar to the 737NG (not prevent stall as the media seem to be so hooked on).

I can't imagine that Boeing anticipated the combination of conditions the pilots encountered, or even the repeated MCAS trim actions that accumulated so much. If they had, I am confident they would have done something different with the either the Max design, the FCOM and/or the pilot training. Furthermore, I doubt Boeing anticipated notion that the MCAS would create such an adverse trim condition at higher speeds than normally encountered during the takeoff climb. The higher speeds the accident aircraft reached would have made manually correcting the trim practically impossible for the pilots to achieve (ref the Mentor video).

[runner1021]

Originally Posted by FGD135

Not difficult to rotate the trim wheels under certain circumstances, but impossible.
IMPOSSIBLE.
Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).that
The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.
IMPOSSIBLE.

Hard to imagine that Boeing didn't include a WARNING in the flight manual advising that above certain speeds manual trimming of the stab would be extremely difficult, if not impossible. Surely they must have encountered this situation during flight testing. In their efforts to hide the MCAS system, they failed to make operators aware of a potentially deadly scenario.

[KRUSTY 34]

Originally Posted by FrequentSLF

thanks, yes i meant that would be pretty hard to operate the manual,trim under high loads, sorry for the confusion i might have created

No worries mate.

Glad we cleared that up.

[jimjim1]

Originally Posted by NSEU

Wouldn't the accelerative forces apply to the vane and the counter balance about the pivot point? So possibly no rotation due to equal forces up/down around the pivot point. I also recall the vanes stay roughly where you put them. They feel fluid-damped.

Yes.

That is what happens when everything is working correctly.

The suggestion is that the observed changes to the AoA signal recorded by the FDR can be explained if it is assumed that the vane has fallen off thereby unbalancing the system and making it susceptible to AoA signal changes with changing Vertical Acceleration (g).

[FGD135]

Hard to imagine that Boeing didn't include a WARNING in the flight manual advising that above certain speeds manual trimming of the stab would be extremely difficult, if not impossible. Surely they must have encountered this situation during flight testing. In their efforts to hide the MCAS system, they failed to make operators aware of a potentially deadly scenario.

Boeing did include exactly that warning in the flight manuals, but deleted it - no doubt, due product liability concerns.

[EDLB]

Seems to me that the final hole in the cheese which dictated the outcome of both flights is, that at higher speeds the trim is jammed (in the direction of nose up) if trimmed nose down. On the Ethopian flight a single nose down command by the MCAS system was enough to seal their fate.

I do not believe that in the time where they clinged on the column for nose up, that they did not try to use the trim switches to unload the back pressure. Elevator trimming you learn from day one in your SEP trainer.

On the Lion air you can see that the PF did constant fight the MCAS AND trim with nose up. As soon as he transferred command there are only few blips of nose up trim to see on the FDR. Same here on the Ethopian flight.

I can’t believe that you only try with two short blips if the landscape becomes larger fast.

[rmac2]

Originally Posted by FGD135

Not difficult to rotate the trim wheels under certain circumstances, but impossible.

IMPOSSIBLE.

Picture the stab, angled leading-edge up (trimmed for nose down) - then picture the elevator, attached to the rear of the stab, deflected up (to achieve nose up pitch).

The down force at the rear of the stab (due to the elevator deflection) makes stab movement IMPOSSIBLE above a certain speed.

IMPOSSIBLE.

The more this subject is examined the more convinced I am that it will be IMPOSSIBLE for the MAX to retain its certification in current form. A quick fix is not going to cut it. No regulator will put their head on a chopping block over it.