Boeing 737 Max8 Aircraft Crashes and Investigations [Part 2] 44

[Alistair_Heaton]

This thread is a continuation of:

thread815-445840


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Another 737 max has crashed during departure in Ethiopia.

To note the data in the picture is intally ground 0 then when airborne is GPS altitude above MSL. The airport is extremely high.

The debris is extremely compact and the fuel burned, they reckon it was 400knts plus when it hit the ground.

Here is the radar24 data pulled from there local site.

It's already being discussed if was another AoA issue with the MCAS system for stall protection.

I will let you make your own conclusions.

 

[waross]

Thank you SparWeb.

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

 

[Alistair_Heaton]

"but my excuse is the scope of the design work I do usually involves using the aircraft within its existing envelope, not expanding it."

That's the thing with the Leap engines they don't per say provide more power. There is an expansion of envelope but that parameter is range.....


The reason why the range goes up is because the LEAP engines sip fuel.

737 500 uses 2700kg of fuel an hour in the cruise.

The leap engines use 1600kg on the A220

The Airbus Neo my mates tell me is easily beating its advertised 20% fuel saving per seat mile that was advertised in the marketing.

 

[LittleInch]

It's a drastic difference compared to the original 737, I agree, but model by model it just sneaks up.

Therein is the key. incremental change from one upgrade to the next upgrade is the underlying issue compared to continually comparing it to the original. A similar thing happened to the BOP on the Deepwater Horizon where the depth of the system gradually crept up m by m until it got beyond it's operating envelope.

I suspect this would be such a big change that it would cause chaos, but really is what should be done.

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

 

[itsmoked]

incremental change from one upgrade to the next upgrade

I suspect some of that is, 'look it creeped and showed no nefarious results'.

'Let's creep it some more...'

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

...there's no fine line to be drawn.

Policy makers should try to avoid bifurcating a spectrum.

A spectrum of possibilities that has been arbitrarily divided into just two choices inevitably leads to endless arguments at the sharp boundary. And worse, being forced to accept a process that is either clearly too little, or clearly too much.

At the very least, policy makers should include a minimum of three options.

E.g. for airworthiness change categories, Major, Medium, or Minor.

There are some workarounds, but issues remain stemming from this 'cognitive bias' instinct to divide spectrums into only two parts.

 

[LittleInch]

VE1BLL

I agree but it still doesn't stop the boundaries issue and the medium category sounds like "a little bit pregnant".





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

 

[IRstuff]

Of course, the FAA has had a continual issue with its organizational mission conflict of interest, i.e., regulate, AND promote. That's an inherent bifurcation in the fundamental psyche of the FAA.

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]

BTW you think the FAA has issues.... you should see what the Australians have to put up with.

And in the JAR days in Europe they stipulated that hot air balloons needed an airspeed indicator. And EASA has continued in the same vane.

So its a world wide issue. Nobody seems to want to pay for proper regulation and oversight.

 

[BrianPetersen]

Seems that there isn't any protection against stupidity ... like enforcing meaningless dumb technical requirements while not checking stuff that actually matters.

An airspeed indicator on a hot air balloon is easy. Just print out a big "0" on a mailing label and stick it somewhere, and call that the airspeed indicator.

 

[Alistair_Heaton]

The fact is that these regulation agency's these days employ more lawyers, phycologists and other blunty types than engineers and operators.

The JAR lawyers didn't have a clue until a lady from Humberside in the UK who told them not to be so bloody stupid and explained the reason why.

They wanted a fully certified ASI and it checked and calibrated as per normal avionic regs, so every 3 years for private operators and every year as commercial.

 

[Sparweb]

E.g. for airworthiness change categories, Major, Medium, or Minor.

Actually, if you read the advisory (And I don't blame you for not reading it. REALLY, you probably shouldn't) they use these terms:
Significant / not significant
Substantial / not substantial
There's no middle ground. Nobody is "a little pregnant" as LittleInch put it.

When you're plugging in new boxes and drilling holes for the wires to run through, you definitely do NOT want to do anything that provokes either "substantial" or "significant" or your project budget triples. It seems a little odd to extrapolate this kind of attitude from my perspective all the way up to Boeing's business decisions, given their complexity and what is at stake. I still think that's what's going on, otherwise why doesn't the 737 type certificate show the latest models certified to the latest requirements?
Actually, all of the OEM aircraft companies do this, and from their perspective they are making as much use of the design work they did in the past as they can.

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

 

[waross]

I am sure that the argument will be made that an engine placement that requires MCAS intervention at high angles of attack crosses the line into "Substantial" and "Significant".
As I understand the reason, it was not for stall prevention or avoidance, that was a pre-existing function and routine.
The treason for this application of MCAS was that at high angles of attack the extra lift from the further forward mounted engines could reduce the pressure on the stick as the AoA increased rather than increasing it as per the regulations.
That sure seems to be "Substantial" and "Significant".
Time will tell.
Sadly, over 300 souls will not be available to testify as to their first hand experience when the flaws became apparent.

A question that has been bugging me;
Why didn't they just extend the landing gear so that the engines could be placed in the same position as in previous versions of the aircraft?
Is it something to do with operational limits of the standard passenger boarding bridge?
I understand that the front gear was extended, so that tends to shoot down the type approvals argument.


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

 

[LittleInch]

Why didn't they just extend the landing gear so that the engines could be placed in the same position as in previous versions of the aircraft?

Because the landing gear needs to retract.
Longer gear need a bigger hole in the plane which isn't there.
Longer gear has more drag so impacts landing and take offs.
Longer gear will create larger moment forces from the braked wheels needing stiffer mounts.

And I'm not am aircraft designer but this is what I can think of off the cuff.

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

 

[LittleInch]

A bit of research also shows that the latest 737NG is actually higher off the ground than the original 737. This was relatively low to the ground to allow stairs to be loaded on the plane and baggage loaded before the advent of baggage ramps by people on the ground. Smaller engines in 1968...

https://www.latimes.com/local/california/la-fi-boeing-max-design-20190315-story.html

Interestingly I didn't realize that the wheels sit under the plane in a pocket but without covers.

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

 

[RolMec]

Back to MCAS, there was this comment on the reason, why Boeing had increased the MCAS rudder step input from .6 to 2.5 deg.
The cutout of Seattle Times' report of March 18th is attached (can't load up an image from here).
A result of test flights.. so, what do the respective test flights to same setups tell now?
There's not just one direction to look, this automatism saving the plane in one situation might well (again) put it in danger in another one.. or rather, might be insufficient to the real needs in that situation.

I feel that the public should have the right to full disclosure of technical changes in order to take part in the discussion.
I feel as well that aircraft and regulatory specialists from all ends should be involved rather than having one more dangerous situation. Due to "soft factors" like tradition, technical inbreed, usual ways.. you name it.

Thanks so much to everybody here, for all this substantial input and research.
kind regards
R


Roland Heilmann

 

[debodine]

I certainly wish I had access to the Functional Hazard Assessment for the addition of the MCAS. I think it would make interesting reading to see the assumptions.

 

[VEBill]

This is interesting.

IEEE Spectrum, by Gregory Travis, 18 Apr 2019

'How the Boeing 737 Max Disaster Looks to a Software Developer'

 

[MikeHalloran]

VE1BLL, thanks for the link.

I have been a software developer for a part of my career.

I think I reached the unofficial rank of 'Cowboy Coder' (usually used as a pejorative), which for a time was useful to a now former employer, because I could rip up and replace major pieces of code, by myself, with no committees or specifications, and sometimes no source code, in a very short time frame, like in the week before a major show.

My stuff was never shipped to customers.

A government agency other than the FAA required that the code that shipped to customers was written with approved procedures, with voluminous specifications, rigorous reviews, exhaustive testing, regression testing going back to the company's early days, and all the stuff that inherently causes delay in software development. ... so much delay that some problems were fixed with hardware changes, because it was faster than generating formally approved software.

The FAA must be at least as fussy as that other agency about software development, so I'm concerned about time estimates on the order of a small number of weeks to modify the MCAS software.

Maybe Boeing has a few Cowboy Coders working ahead of the official teams, pointing the way, or maybe not, but I'd feel more comfortable if they had teams of hardware and software and aero hackers working on a higher level, with no a priori restrictions on what could be tried. ... Like, for example, designing engine nacelles that didn't produce much lift at high AOA, even if they looked odd. ... and ditching the MCAS entirely, or at least reducing its authority.










Mike Halloran
Stratford, CT, USA

 

[Lou Scannon]

Indeed. Kind of like the secret service model, i.e. "get results", "we don't want to know about your methods", "we will disown you if you are caught". Not quite as sinister as that, but the corner cutting applies.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[VEBill]

The process is, of course, DO-178 of whatever version and various Design Assurance Levels.

The word "Assurance" seems to be a case of over-selling; based on these occasional incidents. The investigation will hopefully examine that larger question.

Do we need even more detailed development process? Or is the entire proof of compliance approach doomed to peak at about 99% Assurance coverage because of some subtle Gödel-like proof limit that nobody has yet noticed?

There are companies / products that explicitly avoid getting tangled up in DO-178. They highlight, "No software, firmware or programmable logic." Example