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

 

[VEBill]

"These flaps?"

No, these ones...

 

[thebard3]

Those NASCAR flaps are less about keeping a car from rolling into a ball than to keep it from flying into the stands. There have been several close calls.

Brad Waybright

It's all okay as long as it's okay.

 

[Alistair_Heaton]

I reckon you could get it through certification.

You would need a back up system though.

Maybe hydraulic or electric actuator as primary and the spring system as backup. That would get you past the bar.

They might go for just springs and mcas II as well.

 

[VEBill]

There'd be a pretty good back-up system on the other engine. i.e. there'd already be two, one on each engine. At the cost of some asymetry while the nose is forced down.

I presume that these engine cowlings are not such fantastically-amazing wings that Boeing has an opportunity to remove the actual wings from the fleet. Presumably any small improvement might be sufficient.

...

Or,.. Each mechanical gadget could be split into two independent sides, each using half of the available width. Two in one, where either half is just enough, and both is still okay. Easy built-in redundancy.

 

[moon161]

Maybe hydraulic or electric actuator as primary and the spring system as backup. That would get you past the bar.

Spring to deploy, actuator to retract. Fail safe system.

 

[Alistair_Heaton]

Yep that would work. With the split tab above.

So who is going to email Boeing?

 

[waross]

We have to manage a fix that can be approved quickly.
We have to manage a fix that can be applied cheaply.
We have to manage a fix that will not require simulator training.
We have to manage a fix that will not expose us to any greater liability than we already have.
We have to manage a way to get our fix approved.
It is way past time to end management hubris and end engineering by management decree.
It has been stated that modifying the landing gear would require redesign and re-certification.
Consider the extra forces on the wing generated by the uplift of the larger engines multiplied by the greater mechanical advantage of the more forward placement of the engines.
I hope that the wings were redesigned and approved for these extra forces.
With premature cracking of the pickle forks on the NG, I hope that the pickle forks have been redesigned and approved for these extra forces.
Over the course of my career I have done a lot of trouble shooting.
I can't count the number of times that I had to remove someones else's attempt to address the symptoms of a problem rather than determining and fixing the root problem.
Once a design has started down the wrong road, it is good economics to try to save as much of the original design as possible.
In the case of the MAX engine location, it may not be possible to save any of the original design.
It strikes me that the root cause of the problem is an inappropriate engine location compounded by engineering by management decree.
There may be more than one solution to the base issue of engine location:
Higher landing gear.
Through the wing engines.
Above the wing engines.
Tail mounted engines.
By the way, I understand that the MAX 10 had extending landing gear.
Did the MAX 10 require simulator training because of this?


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

 

[VEBill]

"Spring to deploy, actuator to retract."

No. I was envisioning using air pressure (i.e. the low pressure of the unwanted lift) to cause deployment, working against calibrated springs. Retraction afterwards is thus inherent.

Think in terms of how a pressure relief valve (plumbing) works: a Thing and a Spring; nothing complicated. Well, in this case perhaps several Things linked by simple levers.

There are over-center type mechanisms to include some hysteresis if required; stay deployed until things are back to normal.

Just in case the lift arises from excess pressure on the bottom surface of the engine cowling, then the pressure sensing plate could go inwards, and the lift-killing flaps are extended with hinges and levers (if the plate's movement itself is insufficient).

We've all seen endless examples of simple mechanisms that embed an inherent safety, self-governing, or adjustment capability. The famous Otis elevator brake. Flywheel governors. Rear tires on Top Fuel Dragster that grow in height to provide a built-in gearing. Should be feasible.

By way of exaggeration to make it clear, attach the cowling panels with calibrated Velcro strips. Excess lift will rip them off, ruining the lift. Not a serious suggestion, just intended to make the basic point clear.

Happy New Year!

 

[Alistair_Heaton]

nobody knows about the 10 because it was never certified for flight, all the other stuff stopped it. The Ryanair slave hold class cabin wasn't certified either and that has issues as well and they have said it won't be ready until after June. It needed additional class 1 emergency doors.


As for the pickle forks your guess is as good as anyone on that score. Its gone extremely quiet on that subject, Its running at 6-10% failure rate of 21k cycle aircraft and there is no link with winglets and they haven't released any link to batch numbers for dodgy materials or manufacture. There was rumours about certain parts being meant to be laser profile cut to within a ball hair tolerance. And when there was an audit it was discovered that they were being cut with jigsaws and battery powered hand drills. After the initial release it went very quiet on the subject with a Boeing statement that the parts were within tolerance. Quite how you can go from a 25deg temp soak laser profile cut with post cold working reaming to hand jigsaw profile and hand drilled with a Walmart budget hand drill tolerance being acceptable is anyone's guess.

 

[waross]

I wonder if the pickle forks on any grounded, high cycle MAX 8s have been inspected since the NG issue has surfaced.




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

 

[Alistair_Heaton]

There aren't any high cycle MAX's Even if the first one was put into service and has done 8 sectors a day since they started flying it will be less than 6k cycles in 2 years. The pickle forks are meant to last 91k cycles.

 

[LittleInch]

That extending leg on the 10 was only at rotation and touch down. Once the full weight came on it was the same height as the normal planes.

It did have some fancy linkages to pull the wheel back to the same length as the normal ones when it retracted but it wasn't a fix for the larger engines.

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

 

[davefitz]

Well, if you like design by management decree, then you will just love design by crowd-sourced comments.The design progresses the same way that the plot of the Snakes -on-a- Plane movie was developed.

The pickle fork comments that indicate the fabrication process was cruder than spec suggests that pre-existing cracks were built into the forks, and since a crack has a stress concentration factor of 5, a much lower fatigue life will result.

let's summarize:
design by management decree
engineer's cautions thrown to the wind (re: using only one AoA sensor, also amplifying MCAS correction based on low speed factor)
emasculated regulatory process, AKA corrupted regulatory process
fabrication specs ignored, QC rubber stamped
computer programs outsourced to 3rd world subcontractors with zip aerodynamic expertise
digital control system controlled by a 1980's microprocessor
zero information on MCAS presented to pilots

What could possibly go wrong? Time to become very friendly with some appeals court judges.






"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[waross]

Yes, I understand that LittleInch.
The thing is that any suggestion to raise the plane is met by naysayers.
I think that it just happened again.
The landing gear cannot be changed for multiple reasons, but the gear was changed on the MAX 10.
I am sorry but I still see this as a management problem rather than an engineering problem.
Fast, Cheap, Good;
Pick two.
Well, with almost a one hundred billion dollars worth of aircraft grounded for what may be over a year, Boeing's choice was neither Fast, nor Cheap nor Good.
At 1% interest that's about 2.6 million per day. If the grounding goes much past a year interest at 1% will pass a billion dollars.

The plane may have met the requirement that the control forces must increase proportionally, (Until it didn't).
I doubt that this type of fix was anticipated when the regs were written.
Had the regulation been interpreted as the raw control forces rather than the augmented forces on the stick, the MAX would never have been built with that engine location.





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

 

[waross]

A man had been away from home and out of touch for a long time.
One day he phoned home to his brother to get the latest news.
"Oh, By the way, how's my cat?"
"Your cat's dead."
"That's a terrible way to break bad news.
You good have led up to it slowly.
You could have said;
'Your cat was up on the roof.
We called the fire department for help.
The cat became frightened and tried to get away from the rescuers.
Sadly she slipped off of the roof and died.'
The next time you have bad news, try a little tact."
"I'm sorry. I'll do better in the future."
By the way, how's mother?"
"Mother was up on the roof...."
I wonder if the MAX is up on the roof as well?

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

 

[Alistair_Heaton]

its not really been changed.

The bottom is on a lever arm so it extends 25cm during take off to help with tail strikes.

I don't think it was the pickle forks that had been given the hand drill treatment.

 

[Sparweb]

Thank you everyone for this enjoyable discussion so far!

This topic is being broken into multiple threads due to the length to be scrolled and many images to load, creating long load times for some users and devices.

Please continue the discussion at the new thread: thread815-461989

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