Boeing 737 Max8 Aircraft Crashes and Investigations [Part 8] 24

[Sparweb]

This post is the continuation from this series of previous threads:

thread815-445840
thread815-450258
thread815-452000
thread815-454283
thread815-457125
thread815-461989
thread815-466401

This topic is broken into multiple threads due to the length to be scrolled, and images to load, creating long load times for some users and devices.
If you are NEW to this discussion, please read the above threads prior to posting, to avoid rehashing old discussions.

Thank you everyone for your interest! I have learned a lot from the discussion, too.

Some key references:
Ethiopian CAA preliminary report (Link from Ethiopia is now broken. See link from NTSB Investigations below)

Indonesian National Transportation Safety Committee preliminary report

NTSB Investigations

NTSB Safety Recommendation Report: Assumptions Used in the Safety Assessment Process and the
Effects of Multiple Alerts and Indications on Pilot Performance

A Boeing 737 Technical Site

Washington Post: When Will Boeing 737 Max Fly Again and More Questions

BBC: Boeing to temporarily halt 737 Max production in January

Pulitzer Prize, For groundbreaking stories that exposed design flaws in the Boeing 737 MAX that led to two deadly crashes and revealed failures in government oversight.

http://www.sparweb.ca

 

[RedSnake]

It explained a lot of things I only thought I understood... overall it was good.

I didn't refer to the actual online lecture.
But it was such an echo, so at first I thought it was something wrong with my headset.

It was comment to how the Boing and FAA has handled this.

QRH
MMEL
FCOM
I got most of to, it's just this abbreviations that makes it a little fuzzy..
I probably could make a good guess but then Alister would go on me so I better not

I am not shore how many different types (as in different construction) of AoA devices there are or if they all build on the same principle.
Seems hard to make software one, whit what I know about the function.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

QRH: is quick reference handbook. Basically its a load of checklists which tell you how to deal with various failures and situations. On the max its a paper book where you have to memorise the important ones that need a quick response and loads of others which you can look up then read and do. The modern system is a thing called ECIAS which combines the system which alerts you to a problem with the procedures list of what your meant to do and then monitors the aircraft settings so you don't change the configuration from what's required.

MMEL: Master minimum equipment list. Its the defects you can carry on a flight with various conditions and changes to the procedures. It also gives a time span to get them fixed. which can range from 1 flight to get you back to maint base no pax eg gear locked down limited to 15000 ft speed 240knts and no icing conditions, through to 120 days for things that are really not important like the logo light on the tail. The next document up which we use daily is called the MEL but it can only be more restrictive than the MMEL.

FCOM: I think it has French origins but we use it to mean Flight Crew Operating Manual. Usually comes in 2 parts, one which details the systems and the Part2 which tells you the procedures. They are both pretty meaty with about 3000 pages in each one.

AOA are either vanes that move with airflow or things that are called smart probes which use pressure differences along a pitot tube to work out the AoA. There are other synthetic methods but : don't know much about them because I have never flown anything fitted with them. Q400 had 2 vane AoA's on it. The A220 has 6 smart probes.

Can you reword the question please about feel different pressure. In aviation they use the word feel and pressure quite a bit across numerous systems and its has a different context depending on the system being talked about.

 

[waross]

Can I help?
This is the one that I was wondering about?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[dik]

Boing[/b] and FAA has handled this.]

That's the sound they make when they hit!

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Alistair_Heaton]

Feel diff pressure

Its to do with the hydraulic systems and the force feel system on the elevators. There is power assist on the controls, the feel system applies a force onto the controls which varies with the amount of input aerodynamic loads airspeed
and a few other things. So the more you pull the more more force you feel. Faster your going the more force there is for a given deflection.

The feel computer can use either A or B hydraulic system and when there is a big split of pressure between the two sources it illuminates that light. Quiet how that would be triggered by a faulty AoA sensor i really don't know. I suspect its unrelated.

 

[Alistair_Heaton]

right found out about this Feel diff pressure.

Its a known issue which hasn't been fixed since the feel system was originally certified back in the 60's. But they never bothered fixing it. There is actually a surprising number of "funny's" that have have never been fixed.

https://www.satcom.guru/2018/11/stabilizer-trim.html

 

[RedSnake]

(Edit) I wrote this before you posted the last link, I had not submited it, became distracted since resewing a phone call.
Will edit it or remove it ones a have read your link.. BR A

I assume that this is done to give you the same feeling as if you where flying an all mechanical system.
Without this feedback system you would not have any sense of the forces that are acting on the plane correct?

I also think that this feedback pressure for the the force feel is a calculated value.
Because you can not get a force feel value back from the hydraulic system that controls the angel of the elevators since it is kept in the same position as you want it regardless of the speed air pressure that it is exposed to.

If the force feel is a calculated value, one way of doing it is to take AoA value and combine it with speed and the angel of the elevator, and from this tree calculate the expected force on the elevator that you would have felt, if it was a all mechanical system.
And then the calculated force is feed back to a the controls.

And if it was as in the first crash that one AoA was wrongly calibrated.
The calculated force on the left (A) and right (B) side would have been different.
When compared that would have lit the FEEL DIFF PRESS lamp..
As explained in the video, the left side AoA was connected to computer 1 and right side AOA was connected to computer 2.

I am not saying that this is how it is done, it's just my theory.

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

Sounds reasonable.

Just leave it.

This is very type specific stuff. The other big issue which nobody seems to want to deal with is the Christmas tree lights spread around the cockpit which they had to deal with. As that link shows there is a load of things which will light up but it's not obvious that they relate to any one system failure.

 

[waross]

Is this the section of the very long linked document that we are looking for?.
Please ignore the first line.
It is actually the last line of the previous topic.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[RedSnake]

I was just reading that section..
Haven't found a connection to AoA sensors yet only pitot pressure..
It's a lot to read through.

BR A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

There is a link from the stall system to the electronic feel shift module EFSM.

I can only presume that when the stall system is triggered by the dodgy AoA reading it does something to the feel system.

This is pure speculation though.

 

[RedSnake]

Well as I sad it is a lot to go through.
And it's seems that the link is going through some development faces as well.
Is it so ?
I am just skimming through right now.
This might take some time at least for me to evaluate, since all systems seems to have one or more parts together.

Have a lot of the same things going on at work right now, and it's just chaos. :-(

Best Regards A



“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[LittleInch]

Your link says this about the force when a stall is thought to be occurring. This says it increase the"feel" by a factor of four....

The elevator feel computer has a feature where it creates four times the forces to pull back on the column than normal.


When the stall identification function is trimming stabilizer nose down...

(with the thinking that this is a stall recover, believing AOA perhaps erroneously, and assuming that engine thrust is going to increase rapidly),

...column feel forces are designed to fight the pilot pulling back on the stick (to encourage the nose dropping), and also to avoid the pilot tripping the column stabilizer override switch if they pull it back far enough.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Alistair_Heaton]

Sound sensible LI

So not only did the pilots have it out of trim when the MCAS triggered but they also had x4 feel fighting them pulling the stick back.

 

[RedSnake]

I think I have figured out why the FEEL DIFF PRESS lamp was lit..
Haven't found a connection to the AoA yet, have just finished the hydraulic system..
I might finish it to morrow.
Want to look over it one more time.

Best Regards A

PS. It's a crisis at work so I have to sleep now.
2 technicians who have had 4 months to do a procurement on a motor drive and new servos and I have said since New Year that it will not work and yesterday when they where suppose to sign the contract and the supplier got all my questions they also realized that it would not work.
So now I have 24 hours to fix the documentation and what is needed so they can adjust the contract.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

I wouldn't worry about it Ana. There are so many interconnections between the various systems. I think littleinch has it right.

The problem with all these interconnections is working out what the primary cause is. Because the 737 doesn't have a centralised warning and caution system the pilots have to go searching round to spot all the different indication lights and gauges then take what they see and then work out what the problem is then find the right checklist which may have multiple branches depending what lights are showing.

Modern ECIAS system when something triggers it automatically pulls all the relevant checklists up onto one screen and then on the A220 gives you a white arrow next to the one it suggests as the most important. And it does change depending on your altitude and a few other things.

In my experience you can get 7-8 checklists coming up and then after you have run the suggested checklist then there are 1 or 2 left to run but they are procedure checklist for the new config. Then it automatically changes your normal checklists for any restrictions that are now imposed. If you inadvertently change the configuration away from what's required it then throws the checklist back up and highlights what the required configuration is. Its relatively easy to keep two people monitoring the aircraft while your running the checklists and most of them take seconds. The old paper QRH's you first of all had to get your hands on it then work out what's wrong and then find the right card and start to run it. Once finished you then had to go back and see if there was anything else which required a checklist. If you forget any restrictions or change configuration then human error is the conclusion in the accident report. This can take 10's of minuets.

Realistically the NG should have had this system but they got away with not having it by a margin of a few months. And because the NG doesn't have it then the MAX didn't have it. So its stuck with the same system as the original 1960's 737.

 

[RedSnake]

I wouldn't worry about it Ana.

I do not worry ;-)
It's as with most things a problem a mystery that has stuck in my head.
I need to figure it out, before I can let it go.
Gives me something to do while I wait for the corona pandemic to ease.
I might have bought a jigsaw puzzle instead.
Is everything OK with you?
When you sade that you where home alone (quarantine) does that mean that you are not allowed to see your family either ?

Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

I can see them, I keep them on the farm where its less restrictive living in the city.. But they all came down with covid last week one of the kids brought it home from school. I tested negative everyone else positive 5 adults and 4 children in our extended family bubble.

When I go to work though I have to cross a border and then its full quarantine for the period of work for 2 weeks. I am actually disappointed I didn't test positive that would have given me a free pass for the next 3-6 months from quarantine and testing....

 

[RedSnake]

I am sorry to hear that I hope they all will get well soon.
That must be hard on you not seeing your family.
I have at least chosen my on quarantine.
C.H the only one I would like to see isn't here anymore so it makes no difference to me.
If you get bored you can always come and discuss some traveling at the hobby forum.
I am almost always on line.

Best Regards and be well Anna


“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[Alistair_Heaton]

Its more the constant changing of rules and procedures by the Government and finding ways to jump through the hoop's to comply with them. If you mess it up its 3000 euro fine.