Boeing 737 MAX family NEWS ONLY

1) is not quite correct. They added MCAS to the existing SAS system to correct a tendency to a nose-up attitude caused by the engine placement. And the effect seemed to be fairly minor -- MCAS wasn't there because the MAX aircraft were inherently unsafe with the new engines, it's there so that the MAX planes feel like they are flying the same way as the older NG aircraft. Without it, the MAX would have not had a common type rating with the older 737, meaning that crews would need more training to cross over. It's a result of economic pressure from the airlines.

2) is not at all correct. There is indeed a simple system to disengage SAS/MCAS -- two switches, which the Ethiopian crew used to successfully disable the automatic trim. One significant issue seems to be that these switches don't work quite the same way as the equivalent ones in the older 737s. Older 737s had the option to disable the automatic trim inputs without also disabling electric trim input directed by the pilots. MAX lost that functionality for reasons unclear to me, so both switches disabled the electric trim system entirely. And that's a problem because the mechanical trim wheel seems to be too hard to operate at high speeds, and the crew was unable to crank in sufficient nose-up trim by hand to recover the aircraft. (Also, MCAS switches off any time the crew inputs trim, but the timeout is fairly short, so the fact that it's been disabled can be masked by other events.)

3) is also not correct. a) MCAS is not "flying the plane," it's just providing one trim input. b) the missing annunciator would not have shown that MCAS is providing input, but that there is a disagreement between the two AOA sensors. And that seems to the real screaming problem with MCAS -- it doesn't know how to deal correctly with "AOA disagree" and sometimes makes the worst possible choice based on inputs that should be obviously incorrect. That's a problem the AOA disagree annunciator might help crews notice.
 
it doesn't know how to deal correctly with "AOA disagree" and sometimes makes the worst possible choice based on inputs that should be obviously incorrect. That's a problem the AOA disagree annunciator might help crews notice.
Given the weak amplitude of each MCAS inputs, IMOHO it took on the contrary the safest choice confronted with the opposite inputs: it's much safer to have a slight nose down correction at high speed than keeping what was believed to be a stall situation.*
The main problem is upstream (with the sensor that kept sending its feed despite suffering a catastrophic failure (no torque limiter) ) and downstream with the improper apparent surprising catatonic behavior of the pilots.

*What could have been done is a log of each inputs with a safety factor function of the integral on the time-averaged series of inputs (if not done already).
 
 
Boeing hasn't acknowledged a flaw. In the France Presse* news article, the journalist isn't able to mention the very fact chosen for his headline. What is described here is that the two only dedicated MAX simulator (one for Air Canada and the other one at Boeing) were modified to take into account the real force needed to turn the backup trim wheel...


Notice also how prior to the Ethopian airline crash (and in fact until very recently), this journalist hadn't made a single publication on aviation (I read back his tweet until mid 2017 and the only thing I found was a piece on Quatar airline - then there is a 6 months interruption before there is some tweet specifically focused on the Boeing's Max) just to greet us some fully technical report on the MCAS and Boeing methodologies (that every European born journalist - whatever their respective specialty - seems - it's a great surprise to me - to have heard routinely since birth) and its supposed implication in the accident.


*Tweet are from xxx.ca
 
Last edited:
BBC headline - Boeing 737 Max: FAA says no fixed timetable for grounding to be lifted

"One decision the FAA has yet to make is whether or not to require pilots to undergo simulator training for the safety update."
 
"Shame on you... we're going to call you out on it," Tajer said of Boeing Thursday ahead of a Federal Aviation Administration meeting of international aviation regulators in Fort Worth, Texas. "That's a poisoned, diseased philosophy."

And what are we supposed to rejoice next... Blind Taxi drivers?
 
I find your comment to be in very bad taste.
 
"Shame on you... we're going to call you out on it," Tajer said of Boeing Thursday ahead of a Federal Aviation Administration meeting of international aviation regulators in Fort Worth, Texas. "That's a poisoned, diseased philosophy."

And what are we supposed to rejoice next... Blind Taxi drivers?

Quelle classe...
May I remind you again that the pilots are among the victims too. Plus nothing at this time of the investigation point that they may be to blame.
Seems you dont care... Is it because it happened in Ethiopia ?
 
Last edited:
By the way - thanks for drawing attention to the US pilots union's support for their deceased colleagues.
 
Sympathy has nothing to do there. It's because some are banking on this that we are waging wars for evil. I do not share that reflex of sympathy for those that had the choice (and final responsibility) to turn the outcomes into something benign that they are PIC, Engineers or CEO (it was a pitot tube malfunction for God Sake!).
Regarding the "Ethiopians", you are the one identifying this as being a variable: I do not care frankly.
 
Sympathy has nothing to do there. It's because some are banking on this that we are waging wars for evil. I do not share that reflex of sympathy for those that had the choice (and final responsibility) to turn the outcomes into something benign that they are PIC, Engineers or CEO (it was a pitot tube malfunction for God Sake!).
Regarding the "Ethiopians", you are the one identifying this as being a variable: I do not care frankly.

Well ... maybe decency has something to do here. See ? Respect for some guys who died doing their job, while there is (again) ZERO evidence they did bad. Your mother never taught you that ?
As for Ethiopians being a "variable", your insistence at blaming these pilots while minimizing Boeing responsibility pushes me to ask...
 
You are ridiculous. Where and When did I blame the pilots suggesting their origins being an aggravating circumstance? Don't project your flimsy world on me and other reader. Thanks in advance.
 
You are ridiculous.

Thank you. From you, i take it as a compliment...

... Where and When did I blame the pilots suggesting their origins being an aggravating circumstance?

Never said you did, read again. I asked if it's why you keep blaming them, insisting on their supposed incompetence (btw are you even a pilot ?), as here:
Thank you for the details. I do agree that the value is basically a fully retracted indication. But the flaps in that speculative scenario would have been pulled back due to the pull over (how long time b/w the captor received the value and the actuation of the lock mechanism?).

Anyway It's scary that they didn't land asap. Imagine a cab going down the motorway with a brakes failure inviting you to tight your seatbelt as if everything was normal.

At the end the problem is not in the system that will statically encounters a failure at one time or another but in the operators behind that don't provide the layer of professionalism needed in every failsafe system
.

Here:
it doesn't know how to deal correctly with "AOA disagree" and sometimes makes the worst possible choice based on inputs that should be obviously incorrect. That's a problem the AOA disagree annunciator might help crews notice.
Given the weak amplitude of each MCAS inputs, IMOHO it took on the contrary the safest choice confronted with the opposite inputs: it's much safer to have a slight nose down correction at high speed than keeping what was believed to be a stall situation.*
The main problem is upstream (with the sensor that kept sending its feed despite suffering a catastrophic failure (no torque limiter) ) and downstream with the improper apparent surprising catatonic behavior of the pilots.

*What could have been done is a log of each inputs with a safety factor function of the integral on the time-averaged series of inputs (if not done already).

And even when you try to justify yourself :
As a end note to that digression (and i will refrain to add more until we have some new material), my opinion is very much in concern with:

- The passengers that had to endure an horrible agony and trauma (including physical) - see what happened to teh public in that 747 discussed earlier
- The pilots, the ones that dare to bring back safely a plane compromising somewhat their career with an aborted flight.

Best to all

TC

...Don't project your flimsy world on me and other reader. Thanks in advance.

You're welcome...
 
Faulty parts on Wing LE

Boeing has informed the FAA that certain 737NG and 737MAX leading edge slat tracks may have been improperly manufactured and may not meet all applicable regulatory requirements for strength and durability.

Following an investigation conducted by Boeing and the FAA Certificate Management Office (CMO), we have determined that up to 148 parts manufactured by a Boeing sub-tier supplier are affected. Boeing has identified groups of both 737NG and 737MAX airplane serial numbers on which these suspect parts may have been installed. 32 NG and 33 MAX are affected in the U.S. Affected worldwide fleet are 133 NG and 179 MAX aircraft.

The affected parts may be susceptible to premature failure or cracks resulting from the improper manufacturing process. Although a complete failure of a leading edge slat track would not result in the loss of the aircraft, a risk remains that a failed part could lead to aircraft damage in flight.

LE increases camber hence affect pitch trim.

Source:
FAA via the NPR
 
Last edited:

The knifes are well and truly out:
 
Spirit cuts workweek in wake of 737 MAX groundings: union

REUTERS/Eric Johnson

(Reuters) - Boeing Co’s largest supplier Spirit AeroSystems Holdings Inc is reducing its workweek to 32 hours in response to the 737 MAX groundings, a labor union for the aerospace industry said on Friday.
The changes will be effective June 21 for all salaried, management and executive employees working on commercial airplane programs, the Society of Professional Engineering Employees in Aerospace said.
Spirit said employees have the flexibility to take either Monday or Friday off during the workweek, according to the union.

 
As someone who has done flight control work (and on a Boeing product at that), I have to say I find the design decisions Boeing made in MCAS incomprehensible

First some historical data that's been largely missing from the discussion of the 737 Max losses. There have been at least three fatal crashes including Boeing airliners with air data system failures. Birgenair Flight 301 and Aeroperu Flight 603, both in South America in 1996 and both 757s lost due to blocked pitot-static systems (due to a wasp nest in one case and to a taped over static port in the other), and Turkish Airlines Flight 1951 in Amsterdam in 2009, a 737 lost on final approach due to a failed radar altimeter, which caused the autothrottle to suddenly put the engines into flight idle at 1950 feet rather than the intended 27 feet - despite the second radar altimeter working correctly, and despite the failed reading of -8 feet being nonsensical*. Looking at Airbus, there's the infamous Air France Flight 447 where the pilot response to an air data system issue, believed to have been an iced-over pitot port, led to the loss of an Airbus A330. There's also Malaysia Airlines Flight 124 in 2005, where a software fault in the 777 ADIRU meant a failed accelerometer wasn't isolated, causing a major flight upset, but where the crew recovered the aircraft. Plus Qantas Flight 72 in 2008, an A330, is similar, but with 12 seriously injured by uncommanded pitch-downs, when an ADIRU failed and spammed the system with an incorrect AoA in such a way that the averaging function designed to deal with an AoA data failure didn't work.

So that's four relatively recent hull losses, and a couple of near misses, to remind Boeing that relying on a single point of failure in a safety critical system is not a good idea, and that pilots can become badly disoriented in such cases if information on what has failed isn't high enough profile, one of them a case in which the failure could have been prevented if the air data system had been designed to isolate the failed instrument and rely on the correctly operating one, and another a case in which the code designed to handle an AoA failure turned out to have a loophole.

Flight controls are absolutely dependent on correct air data inputs. In some cases a pilot can look out of the window and eyeball his air data, but that's not possible in instrument conditions, and we get cases like Air France 447 where pilots have overwhelmed a flight control system's attempt to properly manage an incident. There's also the well known somato-sensory illusion where pilots believe aircraft to be doing something other than what they're actually doing because their own body is misinterpreting the environmental cues such as acceleration.

TLDR: air data system failures can be devastating, pilots can make them worse if they misunderstand what is happening. This is common knowledge.

So you simply don't design a flight control system, even a partial one like MCAS, with a single point of failure**. And you make sure pilots know what's happening if it fails.

* Outside of the Dead Sea. But the sudden shift when the second altimeter was showing a steady trend made the failure identifiable.

** Someone suggested that a failed air data sensor should simply turn itself off. And this is a case where wrong data is worse than no data - with no data an FCS at least knows to drop into a reversionary mode and ultimately to hand control to the pilot, who has the view out of the window and his own somato-sensory system to at least give him a chance of working out what is happening. However, while there are some cases in which the sensor failure is obvious, the general case of working out whether an air data input is wrong and isolating the faulty instrument, not the one that's disagreeing because it happens to be working, is massively complex, and can only be done at a central air data computer that's able to compare all its inputs and work out which one is being consistently wrong.
 
Like I said earlier, it's much more easy to deal with a cascading mode of failure upstream (at sensor level) than later on in the chain.

Perhaps that this results from an economical perspective where flight regulators aren't scrutinizing with the same level of exigence the mass produced sub-systems that get buried inside the list of parts of any airliner.

Given the market aggressive move on cost, this is where an instance charged with regulating should justify its own existence.


We have to me here the same footprint of what got MH370 lost because of a set of outdated crash safety systems.

We have to me here the same footprint of what got MH17 lost because of a set of outdated flight regulations (overflight of war zone).

We have to me here the same footprint of [add your own example]...
 
Like I said earlier, it's much more easy to deal with a cascading mode of failure upstream (at sensor level) than later on in the chain.
*

Not if you can't tell if the sensor is wrong, or which sensor is wrong. That you can only tell by looking at multiple inputs from multiple sensors, often over a period of time, and you can't do it at the sensor. And that's overwhelmingly what you have to deal with. The obvious failures are the ones you don't need to worry about, it's the non-obvious ones which make multiply-redundant systems so complex.
 
Last edited:
My remark was about the AoA sensor being ripped half off and still feeding systems with inappropriate data. A simple mechanical device like a torque limiter would have shut it down without any single precious bit of data wasted!
Use an appropriate torque limiter, mount the AoA sensor on top of it and connect the assembly on the plane fuselage... et Voilà !
 

 
 
 
"We need your permission to access your device and use your data". Actually, no. As far as the 737 max goes, it is turning into a white elephant and a hungry one to boot. Just how much money and lost faith is this costing Boeing now?
 
That's nothing new, I'd guess our average salary while developing 777 PFCS was about half that of the Boeing engineers working alongside us. But even they would be earning markedly less than many software engineers working outside of aerospace. If you want to pull back the covers on low wages, it's a much wider story than just outsourcing.

ETA: OTOH I wouldn't classify the crashes as due to software error, it's very clearly a failure in system design, and that's all on Boeing.
 
Last edited:
I don't understand why they are still trying to go with a 'software' solution. It still doesn't solve the problem of the aircraft not flying safely if the software stops working for any other reason while the aircraft is in the air ----
I was reading somewhere, I think either google or Microsoft news, that they have been looking at a hardware solution, not sure how true that is though.
 
Shirley it would be just as cheap or cheaper to completely junk the 737 max program and replace it with other aircraft in the company. Why the big issue when they have alternatives? Boeing are steadily shooting themselves in the foot, one toe at a time.
 

Please donate to support the forum.

Back
Top Bottom