Ethiopian 737

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Chris Foss
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Re: Ethiopian 737 - CG/trim/load analysis

Postby Chris Foss » Tue Mar 12, 2019 12:02 am

Ok, I can't find a specific manual trimsheet for the max, so I am using a 738 sheet for reference.(All wgts in KGs) and hoping the MAX is not far off, but expect the fwd trim limit to be curtailed by the MAX design; heavier engines/trim anomalies due to engine position and shape.

MTOW 78,925kgs

CG range at MTOW = 19-24%MAC (this opens up considerably when the weight reduces to 77,000kgs to 16-28%MAC)

The holds will only take 8377kgs max, but many passengers would be carrying light luggage (UN convention) and unless they hads lucrative contracts for cargo, I would not think they would mix cargo and bags in any one hold (faster/easier offload time) so lets call it 3000kgs cargo/mail/cou in the back and 1000kgs bags in the front

149 pax out of 200(?) capacity, probably grouped towards the front if single cabin class (hence heavier hold load in back)

Depending on fuel, which I would guess is well below max range for this route (unless tankering) to be 10,000kgs

This gives us a TOW of around 60,000 kgs and a probable CG of 20-24%MAC giving us a trim reference of about 50.

Slightly further forward than I prefer to give a pilot for his fuel consumption bonus, but pretty central in the CG and trim range.

Please note, if any pilot can give me improved guestimates on loads/fuel I can refine this.

Now, does the climb from ADD and its altitude make sense? to be only 1000 above take off altitude 5 mins into the flight?

Would they have been limited by ATC? because it seems like a steady but VERY slow climb rate and profile until the anomaly from A/c data, and with an underload of possibly 10,000kgs?

Of course, it could be close to MTOW with tanker fuel, and max cargo or excessive luggage. But even then 200fpm climb out??

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Re: Ethiopian 737 TRIM/MCAS

Postby Chris Foss » Tue Mar 12, 2019 12:26 am

In short, MCAS is designed in part to mitigate the trim anomaly of the MAX at low speed to give a pilot a similar feel to the older models so that training and procedure are common.

The MCAS does this by altering trim (stab angle) automatically.

It also provides stall protection by forcing the stick fwd and altering stab angle to prevent the pilot from stalling.

While Airbus have their (much criticised by Boeing pilots) system, it seems to me that the MCAS Boeing system takes even more authority away from the pilots by not only limiting the resultant control deflections from pilot input, but actually countering it.

The basic flaw uncovered by the Lion Air accident is where a faulty sensor makes MCAS believe the pilot is about to stall even at 300kts and so pushes the stick forward and overwhelming the pilots input and strength.

So did this happen with again?

No one knows for sure, but there are similarities based on phase of flight and final outcome as well as reports of pilot comms relating airspeed mismatch and control issues.

The question for me, given the loss of transmission/data 10+nm and about 2mins from impact is whether MCAS could cause loss of transponder signal, loss of ACARS and other systems data transmission as well as loss of control.
Then we have reports of flames and smoke from the aircraft. (as we always do from eye witnesses) But that aside, there are other indications that do not fit the Lion Air profile or sequence.

I am still hooked by the perforated fuselage section that showed no sign of being ejected from an impact crater. No soot, no typical scorch marks and no fragmentation. It was close to the impact crater, but did not seem to come from the impact crater.

There are no reports of debris any distance from the impact site as yet, but I would expect by now that searches have been carried out along its final estimated flight path, so I believe in flight structural damage to be the unlikely cause of the loss of data/transmission.
At the point of loos of signal, or last data transmission, the aircraft was above 300kts and between 1000-2000ft agl (9000asl). Just not fast enough to cause structural damage AND then fly for 2 minutes to end up 10-11nm away.

So again, how does a MCAS failure lead to a cascade of other issues that did not happen on Lion Air.

The trim was fairly central IMO, so even an extreme trim event would have been marginally controllable, at least more controllable than Lion Air which was heavy and probably nose heavier than ET.
To surmise, I have serious doubts that MCAS was the root cause. It may have been the consequence of another event (avionics fire, uncontained engine failure, etc), but the facts do not add up, unless somehow the MCAS unit blew up taking trim control and pitch authority with it as well as other systems?? This is a stretch to think that and MCAS can fail in 2 ways and be a single point failure in 2 distinct ways

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3WE
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Re: Ethiopian 737

Postby 3WE » Tue Mar 12, 2019 2:44 am

Someone has reported airspeed indication problems and speculation that maybe this IS something of a Lion Air repeat.

Not sure if Boeing is doomed, but Evan will be greatly emboldened.

And are Gabieee and 3BSie naïve in suggestion of known robust power and attitude 'settings'?
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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 2:59 am

I just saw the theory that this could be airspeed related MCAS data instead of AoA related, but with similar outcome.
I can't say exactly why, but I really doubt that as the fix would be the same: pull the breakers and wind back the trim.

Having airspeed mismatch would continue to be a challenge, but they had plenty of actual speed and time to do the procedure (I doubt any MAX pilot is unaware of Lion Air and the advice from Boeing) .

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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 3:12 am

And could Boeing really design a single point failure with multiple failure modes?

No one is perfect, but that would NEVER pass certification even if the circumstances of Lion Air had been overlooked during testing and certification.

These guys are too good.

I am more convinced that the sequential failures and reports from the pilots, while following many patterns of Lion Air, is not directly related.

How would we be looking at the possible causes if it was an aircraft that did not have (or need) MCAS?

Without ruling MCAS out, the evidence must be examined with a much broader scope and investigators usually look to eliminate possible causes or sequences before they try to isolate the actual cause or causes. If exterior sensors were damaged by something else, like a drone swiping off a Pitot tube and AoA sensor which are not far from each other, could lead to this scenario. But that does not account for the sequential loss of airspeed indication, loss of control authority AND loss of transponder, ACARS, etc.

My fundamental question still stands: If MCAS was a root cause or even early in a sequence, how do other completely unrelated systems fail too as a consequence?

The only way to in my view is structural damage from overstress due to aerodynamic forces, which would mean the aircraft is unlikely to fly 10nm further on with such catastrophic damage and we would be finding parts along that flight path

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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 3:16 am

Evan can use his arsenal of weapons to make his own political party AFAIC. Too entrenched in his own thinking to have enlightened discussions with.

(is that trolly enough HB?)

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Not_Karl
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Re: Ethiopian 737

Postby Not_Karl » Tue Mar 12, 2019 5:07 am

(is that trolly enough HB?)
One can never be trolly enough (but maybe Brianie and Evanie think otherwise of 3WEie...)
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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 5:30 am

Easy tiger. Don't make me set the Aussies on you again.

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Re: Ethiopian 737

Postby Gabriel » Tue Mar 12, 2019 7:07 am

They have already recovered the FDR and CVR so, if they are readable, they will have a quite clear picture of what happened in the next few days. How and why that happened will take longer. And how much will they release to the public and when is a different question.

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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 11:46 am

What do you make of this panel?

Not extracted from the crater due to lack of scorch or mud marks, found within yards of the main wreckage.
IMG_2856.JPG
IMG_2856.JPG (174.77 KiB) Viewed 12669 times
Note the puncture marks and spread. Then compare to MH17

I've not seen this on any other aircraft remains. Even PA103 and TWA800 showed out to in fragment punctures.
But never on a ground impact.

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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 11:58 am

I've identified this as the 'i' 'o' of the logo starboard side forward of the engines, so unlikely to be from uncontained engine failure.

All punctures are from out to in.

The regularly spaced scrapes on the lower left don't match the excavator bucket forks.

The top edges of the window frames can be seen along the twisted lower edge. The window at the centre of the 'o' is a blank panel insert.

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Re: Ethiopian 737

Postby 3WE » Tue Mar 12, 2019 12:36 pm

Evan can use his arsenal of weapons to make his own political party AFAIC. Too entrenched in his own thinking to have enlightened discussions with.

(is that trolly enough HB?)
:lol:

I believe he leads a sheltered lift.
Big Wheel.jpg
Big Wheel.jpg (64.54 KiB) Viewed 12665 times
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3WE
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Re: Ethiopian 737

Postby 3WE » Tue Mar 12, 2019 12:55 pm

Evan can use his arsenal of weapons to make his own political party AFAIC. Too entrenched in his own thinking to have enlightened discussions with.

(is that trolly enough HB?)
As much as the guy bugs me, if the aeroplanie incessantly noses over because one not_mega reliable sensor thingie says imminent stall...

...IF true, I'm not interested in curtains or stock prices, but what the hell were the aeroengineers (who are smarter than aggies) thinking?

Cue black and white Evanie rant about the horrors of cost management, capitalism and six sigma MBA intern projects.

If it is something to do with this system- a deep dive into human factors...I said, there, (to Gabiee) that I don't think trim runaways are that unheard of, nor that difficult to address...sure a few seconds of WTF, but when you have 8000 feet of altitude to pull CBs and crank manual trim wheels...

...or is it the much discussed inability to function without airspeed indications?...It's a primary instrument to me, but I also know a light aeroplanie pilot or two who has experienced a frozen pitot and lived to tell the story (admitting that it's probably not as easy to overspeed Hershey bars).

...or is it a Puppy mill issue...(even though they can fly the hell out of RJ's with a very awesome record).
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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 2:43 pm

It's a classic case of creating an unrecoverable problem in the process of fixing one. But obviously not nearly as simple as that.

Let's look at this from 2 perspectives:

1. The accountant.

They think and operate in the long term interest of the company, oblivous to sentiment and morals, their work is only apparent on the bottom line.

Let's say we are having 3 accidents a year through pilot error relating to inadvertently stalling the aircraft and its costing the airline 3billion per year through compensation, lost sales, etc,
The manufacturer offers the airline a product that will eradicate the problem, but the system is not perfect and will fail once a year causing a crash each time.

The accountant will look at the cost of the system compared to the cost of retracing all the pilots, add these numbers to the 3:1 accident ratio, calculate the difference and send his numbers to Evan for validation.

2. The passenger

Simply interested in getting to beach at the lowest price and in one piece.

His priority at the time of purchase is price because air travel is relatively safe and it'll never happen to them.
They've heard all the stories of pilots stalling their aircraft and killing everyone, but 1:30m are good enough odds to not worry.
But then he has a choice of booking a flight on a 757 or a 737 MAX. He's read the stories and looked at the statistics, but the thought of his pilots fighting a machine and losing is repugnant compared to a fellow human making a mistake.

The CEO of the airline has to make the decision based on the marginal bottom line of the company and that's where we are these days.

Once public opinion is motivated or not, he will usually regret the decision one way or the other.

The morality of air safety has wavered between the numbers and the public perception which also affect the numbers.

Flight crew, designers, engineers and flyers are squeezed in the tightening void between these issues.

Trouble is, the way public opinion is going these days with reality TV morality and judgement, we are skewing that equation beyond the ability of companies to manage the
fall out or make the best decisions.


Ok, I hope that keeps Evan's dummy in his mouth and I'll move on to MCAS on the next post and give my view on the specifics

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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 3:29 pm

MCAS - Maneuvering Characteristics Augmentation System

Why?

When designing the 737MAX, Boeing saw a need and filled it in the cheapest way they could: bigger engines and better avionics on a trusted airframe.
A tried and tested way to upgrade an airframe to be competitive and desirable to the airlines. But the airlines don't want to save money only on the ticket price, they also do not want to spend extra money on additional training or infrastructure, so this becomes the design specification for the designers.

Their solution of even bigger engines on the MAX came at a price: the bigger engine needed to be moved forward and up to operate on the same wing structure to be viable which changed the CG and most importantly the aerodynamics at low speed.
What they found was that at the margins of stall, the Cp was moving forward due to the additional lift around the big engine nacelles which also have a more forward moment arm.
So as the wing loses lift, the nacelles are gaining lift, especially at higher thrust settings which keeps the airflow attached to the upper surface of the nacelles.

So as a result, as the MAX approaches stall speed, it wants to pitch up even further.

Pilot feel:
Flying an older 737, a pilot approaching stall will feel some feedback force on the stick and by instinct and training, will know what amount of force needed to maintain attitude/airspeed/controllability.
But the MAX will have a completely different feel and feedback. So much so, that extensive and specific training will be needed to retrain pilots to an acceptable standard of operation.

That conundrum was solved by a magic box that prevents the pitch from exceeding critical alpha while providing feedback forces to the pilot that they are familiar with.
It does it as a function of airspeed, AoA, thrust and CG.

This should allow any pilot to transfer seamlessly to the MAX from older 737s.
Do they need to spend money on explaining to pilots how/why they did this? They didn't think so.

Failure modes

During certification, it is not the FAA that designs the tests or analyses the potential failures, it is Boeing who test themselves and show FAA all data and logic which the FAA either certify or not.

The cynicals will obviously say that Boeing will just create easily passable tests and in a way that's true, but not in the way they think.

Instead of creating a stand alone system with yet more sensors and complex integration, they use existing sensors and just share that info, since all those sensors have been certified and have worked for years without issue. Even their failure modes have been tested to the hilt so the effects are known and procedures created and trained in so crews can effectively deal with any type of failure or more importantly, any consequence of a sensor failure can be managed safely.
After years of service and accumulated data, they were confident that it was better, cheaper and quicker to use that data as part of certification.

Redundancy
To pass muster, a level of redundancy and authority was created for those critical sensors so that any unlikely individual failure can be tolerated without too much fuss.
And again, operational experience has met or exceeded the certification standards so is demonstrably sufficient.

It seems incredible, but assumptions seem to have been made that MCAS will handle s noir failures in the same way that they affect other systems like AP, stick shaker, stall warning, etc.
Again, it is way more complex than that and Boeing will have been required to demonstrate actual failures, consequences and procedures that maintain an acceptable level of safety and redundancy.

It is complex because we are entering a new kind of logic and interconnectivity in the wired and wonderful world of automation and computer programmes.
Most engineers of old could look at a mechanism and instinctively spot its weaknesses and failure modes. It was easy linear thinking based on experience.
Now, computer engineering will be above the experience based of structural, control or aerodynamic engineers who look at these as magic boxes where data goes in and instructions will come out.
Failure modes will be hidden to those that don't understand the complexity of computer logic, so they have to trust what the nerds tell them and integrate their systems and designs based on what they are told will happen.

Coffee break....

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3WE
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Re: Ethiopian 737

Postby 3WE » Tue Mar 12, 2019 3:35 pm

[Two posts up Chris goes philosophical on cost:benefit:unforseen negative effects]
I think it's much more simpler than that.

We know we COULD try to equip each seat with a hellaciously fancy, heavy, airbag-and-parachute-equipped ejector system...but yeah, prohibitively expensive AND has it's own likelihood to malfunction and kill folks...we get that.

The question is much simpler- Did we really build a "stupid" system that's going to force the plane into a death dive when one known-failure-prone sensor craps out and you recognize that roughly once a year a well-trained, well-meaning crew is going to be snookered and unable to address it.

It's not a grand societal question, it's simply: "Did the aero-engineers botch it?" (Disclaimer- I am sure they thought long and hard about it, but it sure looks like a crappy, trappy design from where we are sitting behind computer keyboards- and now we have two brand new planes that dove out of 8000 feet for suspicious reasons.)

[Post immediately above noted- which may hit closer to this question]

(Cue 1950's adversarial discussions of pilots vs. aeroengineers).

(I do know that no way can Gabriel describe this issue this succinctly- so I don't totally trust aeroengineers... :-) )
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Chris Foss
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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 4:39 pm

Of course you understand that the intention was a bullir proof design that matched the flyability and safety record of the 777.

The internal arguments between strapping on more complexity in the guise of simplicity vs creating a dedicated airframe must have caused a few fists to come down sharply on board room tables over the years

But the horrible truth is that even companies as big as Boeing cannot extend financial exposure as much as the used to for increasingly marginal gains.

We have reached a saturation point where design improvements are just picking the bones of an old carcass.


The danger in condensing complex engineering into palatable sound bites for general consumption is that the true understanding of the issue becomes diluted into a moral argument of fundamentals.

Like many, Boeing is a victim of many many thousands of individual design masterpieces (budget and logistics allowing).
This is almost a subversive complacency relying on the performance expectations of past successes.

I can assure you that the internal multi-departmental emergency meetings will be facing the full and horrible reality of that complacency, but the truth is that accountants run companies now, not the talent. And the sadder truth is that without the accountants, the talent would be out of work as other companies exploit the advantage vacuum that would be created if the 'went back to basics'

Our insatiable demand for cheaper travel is the root cause.

If everyone picked their flight because of safety and service above price, we'd see very different aircraft above our heads right now.

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Re: Ethiopian 737

Postby flyboy2548m » Tue Mar 12, 2019 4:41 pm

My head hurts.
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Re: Ethiopian 737

Postby 3WE » Tue Mar 12, 2019 4:44 pm

My head hurts.
Go fly a highly automated cracker box. Perhaps they have achieved the wonderful dumbing down of airmanship.

Maybe we have made enough progress that you guys have finally learned that pulling up relentlessly can sometimes result in a stall.
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Re: Ethiopian 737

Postby Chris Foss » Tue Mar 12, 2019 5:04 pm

As an analogy:

I have an old RC transmitter where I know the functions so well, I can easily use mixing and rates to literally tune an aircraft's performance and control response to fly and feel just the way I prefer, but the 35Mgz frequency was prone to interference and some models were lost.

The choice was to spend another £500 on the latest 2.Ghz set that had a stellar performance, buy a £70 2.4Ghz module to convert it or stick with the old way.

Since the module gave me the reliability I wanted while retaining my expertise and ease of use at a price I was willing to pay, it was an easy choice.

But in doing so, I added an additional interface with complex electronics to ensure input commands and adjustment retained the same outputs, effectively doubling the chance of something failing.

But the hidden issue was functionality of already complex systems like failsafe mode where the 2.4Ghz receivers have their own failsafe mode which conflicted with the transmitters failsafe features.
This lay buried for years until it reared its ugly head and there was a marginal signal loss due to low volts on the aircraft's battery.

Long story short, a model was lost but had I read the phone book of instructions, i would have known what to do.

My old method of regaining signal triggered an Rx failsafe mode that retains its last commanded position rather than shuts off the throttle and sets trim to slow flight, I had to watch my new aerobatic ship do huge high speed loops, each one getting lower until it spread out like a balsa fart across the field.

Only the loss of the aircraft motivated me to explore something I didn't know existed.

And that's the paradox of MCAS.

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Re: Ethiopian 737

Postby Rabbi O'Genius » Wed Mar 13, 2019 6:29 pm

FWIW
Canada's transport minister said it had received new evidence about the crash.
Marc Garneau said that satellite data showed possible similarities between flight patterns of Boeing 737 Max planes operating in Canada and the Ethiopian Airlines plane that crashed.

He said: "As a result of new data that we received this morning, and had the chance to analyze, and on the advice of my experts and as a precautionary measure, I issued a safety notice.

"This safety notice restricts commercial passenger flights from any operator of the Boeing 737 MAX 8 or MAX 9 variant aircraft, whether domestic or foreign, from arriving, departing or overflying Canadian air space.

"This safety notice is effective immediately and will remain in place until further notice."
https://www.bbc.com/news/business-47553787
......never send to know for whom the bell tolls; it tolls for thee. – John Donne

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Re: Ethiopian 737

Postby Rabbi O'Genius » Wed Mar 13, 2019 6:51 pm

......never send to know for whom the bell tolls; it tolls for thee. – John Donne

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Re: Ethiopian 737

Postby 3WE » Wed Mar 13, 2019 8:21 pm

Will there be an associated effort to address the lavatory sinks before the death and bathroom trap is returned to service?
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Chris Foss
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Re: Ethiopian 737

Postby Chris Foss » Wed Mar 13, 2019 9:32 pm

Just hand out parachutes until they can get some duct tape on the sensors. That way you can just point it to its destination and save on pilot training.

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Re: Ethiopian 737

Postby ocelot » Sun Mar 17, 2019 7:36 am

What do you make of this panel?
I might suggest "tree", but there apparently aren't any anywhere near the crash site...


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