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Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]
3

Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

(OP)
This is the continuation from:

thread815-445840: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1]
thread815-450258: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 2]
thread815-452000: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 3]

This topic is broken into multiple threads due to the long length to be scrolled, and many 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.

My personal point of view, since this falls close to (but not exactly within) my discipline, is the same as that expressed by many other aviation authorities: that there were flaws in an on-board system that should have been caught. We can describe the process that "should have happened" in great detail, but the reason the flaws were allowed to persist is unknown. They are probably too complex to reveal by pure reasoning from our position outside of the agencies involved. Rather, an investigation of the process that led to the error inside these agencies will bring new facts to light, and that process is under way, which will make its results public in due time. It may even reveal flaws in the design process that "should have" produced a reliable system. Every failure is an opportunity to learn - which is the mandate of the agencies that examine these accidents.

Some key references:

Ethiopian CAA preliminary report

Indonesian National Transportation Safety Committee preliminary report

The Boeing 737 Technical Site

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I have had a look at Angle of slip sensors.

It appears that to get a real reading using a sensor you need a huge probe out the front into clean air. Certain test flight aircraft have them.

But it seems they use the output from the INS or AHARS, heading and track from GPS and air data computer gives the other stuff, and then derive a angle from that. The slip ball indicator is AHARS derived.

But to be honest its way over the tech knowledge required by pilots of the type on how these things are calculated. Looking at the list of variables outputted by the data recorder it is calculated for my type but how it does it I have no clue.

I suspect that test aircraft are used to calibrate the internal derived data for slip angle and then that's what's used.

To note for commercial aircraft the only time the aircraft is in slip or skid like that is when you are operating single engine and you haven't sorted your rudder trimming out yet and when your doing a cross wind landing. The rest of the time its ball in the centre for coordinated flight. Apart from anything else if you fly with the aircraft skidding all the time you will get ear ache off the cabin crew and increase the likely hood of the pax barfing down the back. And it will increase your fuel burn. I might add the ear ache off the cabin crew is enough that you don't do it unless you want to go hungry and not have a cup of tea while the sun comes up.


To note I have been shown the price list for the MAX and the customer options. To be honest I am a bit scared and won't post it because of all the legal exposure that gives. But the option to give the pilots a AoA indicator on the PFD and additional AoA mismatch warning was utterly disgustingly expensive for a safety addition, for what is only an activation of some code to display a value which is already available and being used for no additional hardware. No accountant would pay that price for something that's not required.

Hell as a Scotsman and pilot I wouldn't pay it either. But then again it was two Scotsmen fighting over a penny that invented copper wire so maybe I am not the best person to do that cost analysis.


Anyway they will all have it now, but I suspect even having it wouldn't have changed the outcome of the two aircraft unfortunately.


RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Just a link from this side of the pond. I can't see that being complete before the end of this calendar year. And I also can't see the other CAA's doing anything until after the EASA review is complete mainly due to cultral face issues if it turns out that it turns up issues which I suspect it will with the elevator power V stab power. If the tail and controls needs redesign and certification we could be talking a year at least.

https://www.bloomberg.com/news/articles/2019-05-28....

And one from Boeing from just before it was rejected by the FAA. They haven't given the reason yet for the rejection.

https://www.boeing.com/commercial/737max/737-max-s...

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

(OP)

Quote (Alistair Heaton)

I have had a look at Angle of slip sensors.

I found an angle of slip indicator for you. Works great in aircraft where the windscreen IS THE Primary flight display.
Think it would work on a 737?
wink

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I am interested in any pilots comments on this statement:

Quote (Boeing Statement)

There are no pilot actions or procedures during flight which require knowledge of angle of attack.
Link

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Everything is referred to speeds for weight which are given for the envelope range.

This then puts you in the correct AoA.

Military pilots of fast jets fly the AoA for carrier landings which means they don't have to worry about the aircraft weight.

For landing you land at 1.21 of stall speed in commercial aircraft. This is a fixed angle of attack.

Civilian world they for some reason which I can't understand do not want the pilots using AoA.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

(OP)
Airspeed is normally a very good proxy for AoA. It is measured fairly directly, in conjunction with other aerodynamic parameters, so you can have a good idea of how fast you are going, not just horizontally but vertically and how high you are, all from two simple tubes.

The errors that build up as you increase altitude grow exactly in proportion to the effect altitude has on your angle of attack, therefore, your indicated airspeed still tells you what you need to know.

Because angle of attack can be changed in seconds with the stick, any device to deliver to the pilot AoA info would have to do it continuously, without lag or overshoots. What would a pilot do with the AoA information on a second-by-second basis that can't be done by airspeed?

Bad things happen when pilots fail to second-guess a faulty airspeed indicator. Would the same happen if they had an AoA indicator, which then went bad?

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Thanks for the explanation, Alistair and SparWeb.

Another question.
I understand that there are several inputs that already caused automatic trim adjustment.
Is speed trim the correct term?
Is AoA information just an added input to the speed trim system with a new name, or is MCAS an additional stand alone system?

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

AoA is one of these things which is progressively getting used more and more. It started just being involved with the stall system but now gets used by various other systems. Eg the FMC to get most economic flight profile settings.

You are correct that you trim for a speed but people don't call it that.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I don't have a clue how it's all intergrated. The base control system is easy enough but when you start looking at what boxes are talking to each other and it gets complicated.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

There is a Speed Trim System on 737s that automatically changes the trim to match the speed. AoA is also used as a correction for the Pitot-Static system to provide accurate airspeed.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

"Speed Trim System (STS)
An electrical stabilizer trim input automatically controls certain aircraft attitude conditions when undergoing large thrust changes in the lower speed region, such as takeoff and go-around. These conditions require high thrust settings and are especially present with a low weight aircraft and a relatively aft center of gravity where the aircraft wants to “nose up”. The STS supports the crew during these conditions when manually controlling the aircraft without the use of an autopilot by an opposite stabilizer trim, commanding a nose down force by use of the autopilot trim.
STS activates:
– Between 100 KIAS and Mach 0.60 (fading to zero after M 0.68)
– 10 secs after takeoff
– 5 secs after releasing trim switch(es)
– N1 >60%
– Autopilot disengaged
– Trim required
A short manual trim selection overrides the speed trim and will inhibit it for around 10 seconds, just in case that the speed trim inadvertently provides an incorrect input.
The SPEED TRIM FAIL light Illuminates amber:
– accompanied by the FLT CONT annunciator and MASTER CAUTION with a failure of the STS
– after RECALL is pushed together with the FLT CONT annunciator and MASTER CAUTION but extinguishes when Master Caution System is reset with a single FCC channel failure.
The stabilizer speed trim itself (not to be confused with STS) depends on flap position as it is most needed with the flaps extended around the takeoff and landing phase.
When the flaps are up, the low speed trim moves the stabilizer at 0.2 ups (units per second) and when the flaps are extended the high speed trim moves the stabilizer at 0.4 ups.
This stabilizer speed trim is available during autopilot operation, than stabilizer trim speed changes when the flaps are up to 0.09 ups and when the flaps extended to high speed of 0.27 ups."


Seems there is another system for dealing with flight characteristics.

Is that the system you mean or is there another one?

The list of what AoA is used for these days is huge and it sneaks in as 3DDave says to do corrections on multiple systems. It its also involved in the rudder systems eg yaw damper.

Quite how the 737 deals its inputs and failure modes I really don't know. With electrical failures its normal for systems to progressively be shed and as the heaters are reasonably high load one side of the Pitot static system is shed, I can only presume one of the AoA vanes also goes but don't know. It could be both of them. But if this then automatically then kills the AoA usage I don't know. If the electric trim has already been shed as well then it won't matter.

On my type we loose what we call the low speed cue which is the stall protection which does give you an idea of AoA but not a real value quite soon in the proceedings. Now if this is due to a safety assesment that its more likely to cause issues than solve them or the sensor is off line I have no clue. The only bit of advice in the QRH when you get it is "maintain a safe airspeed for the conditions" and its a de brief point if you don't work you way through to that checklist for that obvious advice in the sim.

And another punch in the guts for 737 operators if they haven't got enough to deal with just now trying to plug holes timetable.


https://www.cnbc.com/2019/06/02/boeing-notifies-fa...



RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Sparwweb,

My own personal opinion ( based only on the publically reported summaries) is that the reason for the failure to catch the basic design error is neither complex nor complicated, but instead it is too simple to accept publically. The instant problem was just the nexus of 2 common faults in our system of government regulation and corporate management.

In nearly all large companies the weight given to sales success decisions simply outweighs all other considerations, as measured by the corporate internal poltical power given to sales VPs and their commercial decisions ( together with incentives such as bonuses etc) are totally focused on sales success. Likewise, the evolution of our government regulation mechanism has, in all instances without exception, caused the regulators to be "owned" by the regulated industry.This instant spate of fatal accidents will not change either of these systemic defects , and the current effort is merely focused on finding words and narratives to help cover these systemic issues that are integral to our way of life.

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I agree. These incidents are looking less like engineering failures and more like corporate management failures.

I'm sure engineers raised red flags along the way but what are they in the path of an ill conceived corporate agreement to make red lines with green ink.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Based on personal interaction with several Boeing Systems Engineers, I know where I would start digging.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Is there likely to be a commission type thing aka what they had after the shuttle failure of the solid booster o rings in the cold?

Just been reading the book by the engineer that spoke out about the whole thing then took the lead on the redesign.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

(OP)
No.
Boeing is not a public agency like NASA.
Several state legislatures would burn down before that kind of inquiry happened.

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I wasn't thinking Boeing would be the focus of the commission. They were only playing the system.

The system would be the focus of the commission.

They need to do something. If the US system is deemed none compliant by the rest of of the worlds CAA's then it becomes a very difficult market for any aviation product from the USA.


Sparweb just seen the perfect angle of slip indicator :D The first form of HUD ever and works a treat. Failure mode the bit of string comes off.... Effect on flight zero.... Fix another bit of string.....

Unfortunately the boundary layer on the windscreen on powered twin aircraft means it won't work. A few times I have had feathers trapped in the wipers to see the effect.

Oh that's another completely useless system on all commercial aircraft.... the wipers. Highly expensive to maintain, create loads of noise in the cockpit, utterly useless for doing the job they were fitted for. Thankfully centre line lighting does work, as does taxing by brail.

Takes me back to the day.... I came to gliding after doing power. Gliding makes you aware of the rudder pedals even more than flying tail draggers. Can't wait until my kid is old enough to be able to go gliding...


RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

if extrapolating from previous experience (gulf oil spill):
For some company managements there's seemingly but one way to bring them back into conciousness, that's litigation with relevant sums at stake.

Then, did the Boeing system engineers know about the faulty design? i use this word, to be technically clear. That's not an accusation. Did someone there rise the red flag?

This would be the person to start rebuilding the system & also public confidence, similar to Alan McDonald & the boosters for the Shuttle.

Why not respecting, demanding, encouraging diverging technical opinion as proof of soundness within the design world?

Roland Heilmann

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

There seems to have been many red flags.

One of the test pilots has stated that when he tested the system early on there was two seperate sensor systems linked to the MCAS. They had both AoA's in the loop and the aircraft G and it was limited to one input cycle of the reduced amount and you needed to be in the high positive G section of the flight envelope. He still wasn't happy with it and said so. But as the system needed high G as well as AoA input he relalistically couldn't see it activating so with reservations said it was OK.

He has since left Boeing and now flys for a US airline and was as surpised as everyone else when the production system as fitted to the MAX became public knowledge it was very far away from what he had signed off.

https://www.planeandpilotmag.com/going-direct-boei...

https://www.nytimes.com/2019/06/01/business/boeing...

And this article has loads in it how the various flight augmentation systems work on the 737

https://www.satcom.guru/2018/11/737-fcc-pitch-axis...


"This would be the person to start rebuilding the system & also public confidence, similar to Alan McDonald & the boosters for the Shuttle."

Sully could be a face for the team...... But as there are more than likely voodoo dolls of him around the US getting daily stabbings I doudt he would be acceptable to the main industry players. But he would sort the public confidence side of things if he said it was now good.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

In the old days of digital computers, the golden rule was GI=GO, or garbage in = garbage out. To base a critical computer response algorithym on an assumption that a single instrument was fabricated correctly, calibrated correctly ,maintained correctly and not damaged from airfield debris seems to be a gross error.I had thought that components of commercial airliners were designed using probability based on a 3*std deviation proof , but I guess that rule is no longer used anymore

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

IRstuff - control systems or Systems? Was your primary product Powerpoint slide decks and your goal to present at an INCOSE symposium?

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Weapon target and acquisition systems, and I've never been to an INCOSE symposium nor produced any Powerpoint slides for any.

I think it's more than a bit insulting to assume that all systems engineers are paper-pushers; it may be the case that many are, just as there as many designers who don't bother understanding their requirements. The systems engineering process is the minimum threshold required to manage a design, but as with a PE license, it does not guarantee a successful design; that still requires knowledgeable systems and design engineers to produce a valid product. You can look to Uber's and Tesla's fatalities to see identical processes at work with identical lack of understanding of requirements.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

I can look at FCS as well.

I'm looking at the Systems Engineering slides where SEs are the central and controlling figures for the entire development process, considered the sole source of knowledge and their general lack of experience in managing and understanding failure is clearly shown by the manner in which INCOSE supplies the concept that if one just keeps track of requirements and does a pile of AoA paperwork that that is enough.

The way that the process failed in the 737 Max matches my experience with high-level SEs.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

OK, fair enough; I worked on FCS, and it was snafu'ed by by a bunch of problems, but the big issue isn't the systems engineering, per se, it's the lack of knowledgeable SMEs trying to go through the process. As I alluded to earlier, even a perfect process still requires experienced engineers; you can't parse or question requirements that you don't fundamentally understand. Part of the systems engineering process includes a System Requirements Review (SRR) wherein you hash out the interpretations and scope of each requirement; that can't be done with people that have no experience.

This is no different than Uber hiring a bunch of LIDAR and image processing guys that only understand target segmentation, and not target tracking. The end result is that Uber's target processor detected the pedestrian, but ignored the fact that the pedestrian was on an intercept course well before the pedestrian actually got into the path of the car. So, whatever faults Boeing has, it's nowhere unique, since both Uber and Tesla have almost identical issues with processing of targets beyond the basic detection step.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

Quote (IRstuff)

but the big issue isn't the systems engineering, per se, it's the lack of knowledgeable SMEs trying to go through the process. As I alluded to earlier, even a perfect process still requires experienced engineers;
As far as engineers on this project.
I am sure that Boeing managers carefully selected the engineers for the Max project.
It is easy to imagine that any engineer with the moral courage to stand up to management and say:
"This is wrong."
would not be on the team.
One engineer with such moral courage slipped through the net.
When he did stand up to management, and was supported by his team and another senior engineer, he was quickly removed from the program.
I am sure that the engineers did their best.
The best engineers may not have been chosen for the Max team.

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

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

You don't have to try hard to create systems where self-reporting is a precious thing to do. Just basing bonuses and raises on the number of self-reports will passively prevent 95%+ of a team from bringing up an issue. Why should anyone fight too hard if they will likely be on another project,contract, or company in a few years anyways? OSHA in their safety guidelines strongly discourages financial rewards be tired to self-reports. I am sure those engineers at Boeing had a manager breathing down their neck over deadlines. Any pushback would probably be a career mistake. At Wells Fargo, you just had to create unrealistic expectations and make people afraid to get them to be unethical. Companies with poor ethical culture in my opinion more times than not are that way by design.

------------------------------------------------------------------------------------------
If you can't explain it to a six year old, you don't understand it yourself.

RE: Boeing 737 Max8 Aircraft Crashes and Investigations [Part 4]

In the pilot side of things self reporting is a variable topic. I am lucky in my current job that a flight safety report goes to the flight safety department who are separate to the fleet management. And I am pretty happy the way it works and issues dealt with.

For the vast majority of things it usually heads out to either the Engineering side of things or operations. A quick interview to see what the crew did and you get the results a bit later.

If its due to a crew screw up they dig in and find out the root cause. Then deal with it. Thats not to say you can't be fired over something you have submitted if you have been negligent or there is shall we say history. But to my knowledge nobody has been fired for a one off event. Even to the point of structural damage to an aircraft.

Heavy landings are always an issue with any airline especially as FO' come on line and float up the experence curve. Thats not to say Captains don't do them as well. The hardest I have done in the dash was 1.89G the trigger for heavy landing is 2.1G. It was my own fault didn't put enough power in when we got sink in the flare and hit the pitch limit and arrived. Calm winds and 10k viz so no excuse. Apologised to everyone on board and that was that. Must admit when the FO does one I take the blame, well ultimately everything is the fault of the Captain even if its not them flying the aircraft.

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