Boeing 737 Max8 Aircraft Crashes and Investigations [Part 5] 19

[Sparweb]

This is the continuation from:

thread815-445840
thread815-450258
thread815-452000
thread815-454283

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

Indonesian National Transportation Safety Committee preliminary report

A Boeing 737 Technical Site

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

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[IRstuff]

Any substantive re-design is going to cost many additional billions, AND possibly a year or more in time delay.

Of course, EASA wouldn't have ANY parochial tendencies to given Boeing a few digs in favor of Airbus ...

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Alistair_Heaton]

The same effect is more than likely present on the neo as well.

But as there is no control force feed back to the stick its not an issue under fbw certification. For you to lose alpha floor protection you need to go down to the third level of failure mode and even then your not into direct pilot control. There is another level below that.

The problem with the max is that anything goes wrong and the first failure level is the pilot and no protection and control forces changes which are the reverse of any other commercial aircraft and the max when it's working properly.

 

[Alistair_Heaton]

EASA really aren't being difficult due to Airbus. They are pain in the ass bureaucrats to everyone that has any thing to do with them.


Airbus's production lines are full anyway. They seem to have some good product lines which the customers want. Boeing hasn't produced anything new since the 787 came out in 2007 which also had issues with its battery's and it appears to have absolutely nothing in the pipeline. It makes zero difference if the 737 max is flying or not to Airbus for the next 10-15 years. It will have a good effect on powerplant availability for the NEO production line but it won't create any more revenue if the MAX is grounded.

Giving digs to the FAA I could see. But Airbus V Boeing I can't see.

 

[LionelHutz]

787 has about 650 unfilled orders at 10/month that's five years of orders. Not sure why you think that's nothing in the pipeline. It's about the same number of orders as Airbus has for the 350. If you want to talk failures, the A380 should be at the top of that list. Only 321 are expected to be delivered before ending production.

 

[LittleInch]

I think he means new designs of airplanes... 797 anyone?

https://simpleflying.com/boeing-797-update/

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

 

[Alistair_Heaton]

There is nothing new.

It's all grandfather types. And all reaction s to other OEM, brand spanking new clean sheet types.

The nma is 15 years too late.

They haven't even officially started on it.

Boeing still hasn't got a composite spar. Emb, DH and AB have been making them for years.

757/767 is getting well pumped. Btw the 757 with rollers on is one of the few that gets my juices flowing.

 

[SWComposites]

Huh? Boeing doesnt have a composite spar?

Ah, there are composite spars on the 777 empennage, on the 787 wing and empennage, and on the 777X wing and empennage. I worked on the 777 emp ones staring in 1989.

 

[Alistair_Heaton]

It has bits of them I agree.

I think the wing is 50% composite 20% Al 10% steel and 15% titanium on the 787. Can't remember what material the rest of it comes under.

I was meaning the main wings spars. And wing structure

Boeing only got the big autoclave in 2015 for the 777x wings.


The big one went into Hawarden in the 1990's I think.


OH and I completely agree about the A380 slug. Huge mistake by AB management. But the silver lining is that they learned alot from the mistake from an Engineering and production POV and targeting a product. They did it to try and take on the 747 when the airline industry was moving away from 4 holers for pax transport. Since then they have been focusing on aircraft that are actually useful and have a much broader market. I am no lover of Airbus products BTW to work in. But I do admit when travelling in an A380 it is an extremely nice aircraft for long haul much more pleasant than a 747-800.

 

[LionelHutz]

Boeing is working on the NMA, but in hindsight it might have been better to be focusing on the Y1 first instead of putting all their narrowbody eggs into the MAX.

I don't particularly see Boeing as being a non-developer. I also don't see Boeing as flogging old designs any worse than Airbus does. Airbus just doesn't have as old designs to flog. Both Airbus and Boeing currently seem to be capable of bringing a new design to market about every 10-15 years.

Boeing had originally planned to develop the Y1 to be entering the market at about this time. But, they switched to developing the MAX instead and pushed off the Y1 at least another decade. In hindsight, that was a terrible decision. It also seems odd to continue pushing off any 737 replacement development considering the insatiable demand for that aircraft type.

 

[Eufalconimorph]

From

https://simpleflying.com/easa-737-max-test/

"EASA wants Boeing to demonstrate the stability of the MAX during unusual and extreme maneuvers, both with the updated MCAS in operation and with the system switched off." (emphasis mine).

It is my understanding that MCAS is required for stability in certain (extreme) parts of the flight envelope, due to the positioning of the engines. Doesn't that make this test impossible for the MAX to pass?

 

[RVAmeche]

Maybe their intent is to ensure that the system no longer fights the pilot/reactivates itself once it's been disabled and not ensure the MAX can perform those maneuvers without assistance?

 

[Alistair_Heaton]

Here is the original presentation slides.

To be honest although everyone focuses on the MCAS side of things.

The trim system is going to be the hardest one to deal with.

https://www.europarl.europa.eu/cmsdata/186500/20190903_EASA_Ky-original.pdf

MCAS alters the control forces that the pilot feels as they approach the stall. Normally the nearer you get to the critical angle of attack the more force is required on the controls to increase the angle of attack.

Because of the engine position and the lift generated by the bottom of it, this produces a moment which means the force to increase the angle of attack is reduced the nearer you get to the critical angle of attack.

It won't be Boeing doing these test flights it will be EASA test pilots and engineers.

 

[LittleInch]

Hmmmm. The manual trim wheel forces one is going to be interesting. Nothing there about this check of one FCC against the other.

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

 

[Alistair_Heaton]

" Extensive change to the Flight Control Computer architecture and logics (incl. Autopilot
)"

On slide 15, I presume is the dual channel FCC and changes to the relays.

Although the bottom one about no approprate changes to the integrety of the AoA system sort of knocks it on its head.

 

[Alistair_Heaton]

Just a link to the tech pilot 737 max legal issues.

https://www.seattletimes.com/busine...-documents-citing-fifth-amendment-protection/

The next one is just out of interest. they were doing the 777X wing loading final check and a door blew out. Which would have a been a scary big bang if the fuselage was at max differential pressure.

nice pic of the internals of the new 777x wing though.

https://www.seattletimes.com/busine...-documents-citing-fifth-amendment-protection/

To be honest its a pretty poor article. Nobody seems to know if it was a plug door that went or won't of the cargo doors.

 

[human909]

"EASA wants Boeing to demonstrate the stability of the MAX during unusual and extreme maneuvers, both with the updated MCAS in operation and with the system switched off." (emphasis mine).

It is my understanding that MCAS is required for stability in certain (extreme) parts of the flight envelope, due to the positioning of the engines. Doesn't that make this test impossible for the MAX to pass?

I wouldn't quite jump to that extreme. MACS off means that some low probability failure has likely occured, different requirements apply.

In extreme parts of the envelope with MACS off you could have anything between "ooh this makes handling a little bit more challenging but nothing too hard for a pilot who expects it..." to "OMG this is next to uncontrollable and can readily lead to unrecoverable positions".

 

[Alistair_Heaton]

That's the thing though MCAS being off is not deemed low probability. For that it needs to be 1 in 1 million flight hours or flights depending what code your looking at.

The logic is that with the dual FCC then mcas will be off whenever they spot a mismatch with the AoA sensors. That happened twice in under a year.


And the high alphas with manual flight occur when ever there is a terrain avoidance, wind shear and to a lesser extent during a go-around.

I have been trying to think of an example of the effect which none pilots can relate to with this effect.


The only thing I can think of is the brakes on a car. With a normal car the brake force required by the drivers leg increases the nearer you get to brake lock up. If the car was the same as the boeing MAX the brake force would increase up to 90% wheel lock up and then would decrease over the final 10% of travel. So during an emergency stop the driver would have to remember to reduce the pressure towards the end of travel to get best performance. And if they do lock up the brake force would increase as they backed off the pedal. All while trying to stop before hitting a child or hitting a wall or other vehicle. Most of the time you wouldn't feel or experence the effect. The MCAS when its working has a ABS effect of pushing back on the brake pedal increasing the force felt by the drivers leg the nearer you get to lock up. It would be like in a car and the ABS system failed instead of pushing back on your foot then it would change to the brake force on the pedal suddenly decreasing and the travel increasing suddenly when the wheels were about to locked up.

Humans are relatively good at dealing with linear force changes giving a linear effect. We even convert stuff and use cams to give logrithmic changes to controls to give a linear responce for a linear change to the control. Evolution just hasn't set our sensory and motor skills up to deal with with nonlinear feed back and control input. We can sort of do it with lots of brain capacity used. But if your relying on the baser parts of your brain to sort things out which use muscle memory and learned reflexes its a completely different story we generally fail to give the correct responce even with relatively low stimulus loads.

 

[waross]

I am thinking about driving a car in a large, icy parking lot. You keep turning tighter and tighter. As you turn tighter in the old, pre-power steering car, the force to turn the steering wheel increases. Then the front wheels loose traction.
Two things may happen, The car ceases to turn and goes ballistic, and the steering wheel forces become very light.

As I understand the combined action of the uplift and force couple, You loose the feel of the stick, and without moving the stick, the plane may continue to increase the AoA.
I seem to remember one account from testing that indicated that when the stick went "light" the pilot had to, counter-intuitively, push the stick ahead to avoid a stall.
Asking, not telling, but when the stick feel "goes light" are you at, or dangerously close to a point where the AoA will continue to increase into a full stall unless the stick is pushed ahead?



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

It won't increase without pilot input. If it did then it would be unstable and even with MCAS it would not be certifiable. As you get nearer the stall the force required to move the stick back to get closer to the critical angle of attack needs to increase the nearer you get to the critical angle. WIth the max with MCAS off the force does this up to a certain point until the engines start creating significant lift. Then it decreases the closer you get. With MCAS turned on when the engines start producing lift it trims the stab to create more force on the stick so it continues to behave normally like all other none FBW aircraft that the pilot has ever flown in the past.

 

[Lou Scannon]

Just a slight tangent to Alistairs post about car brakes, many probably know this, but traditional automotive drum brakes are designed to be servo-actuated, or self energizing. I.e., the torque applied by the drum to one of the shoes due to intentional geometry, increases the normal force of both shoes to the drum. The geometry is typically such that the self-energizing component of the force is a fraction of the force applied by the cylinder, but is nevertheless significant. This lead to non-linear behaviour as Alistair described. The main outcome, due to the open loop system, was uneven and time variant braking at each corner, hence a tendency to weave under hard braking, which required correctional steering input by the driver to follow his intended path. Obviously not a recipe for minimum stopping distance. Despite this, some all drum brake vehicles back in the day turned in quite creditable controlled braking distances to a stop from 60mph, the humble VW beetle being one. I believe full sized Buicks weren't bad either, after they had introduced their finned aluminum drum design. This after being lambasted on braking performance in Ralph Nader's book, Unsafe at any Speed. /tangent

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz