Boeing 737 Max8 Aircraft Crashes and Investigations [Part 7] 16

[Sparweb]

This post is the continuation from this series of previous threads:

thread815-445840
thread815-450258
thread815-452000
thread815-454283
thread815-457125
thread815-461989

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 (Link is now broken. See PDF download below, 3 MB)

Indonesian National Transportation Safety Committee preliminary report

A Boeing 737 Technical Site

Washington Post: When Will Boeing 737 Max Fly Again and More Questions

BBC: Boeing to temporarily halt 737 Max production in January

www.sparweb.ca

 

[3DDave]

Alistair - Now you've changed your tune, going from decreasing force (wrong) to decreasing force gradient, which is what I wrote. I know about the aerodynamics - that's what the "Aerospace" tag by my name means. Typically it's called center of pressure, but that's not a fixed location with variation in AoA. It does add lift ahead of the center of gravity, which is relatively constant if the only change is AoA, depending on the footing the flight attendants have with the drink carts. It is the position relative to the CoG that produces moment.

The thing is - in the two MCAS crashes the pilots were entirely immune to noticing control forces in any way that prompted the correct responses. With that human factors information the regulation makes no sense. In fact, without that regulation, MCAS would not exist and the crashes would not have occurred.

 

[Alistair_Heaton]

yep we are now arguing about the use of English terms which is different between pilots and engineers and proper English speakers and American. The CoP does change depending what flap setting you have and AoA and the movement is more pronounced on swept wing it moves both forward and back and along the wing laterally. Calling it Point/centre name makes no difference

It really doesn't matter what the pilots did now. The plane was multiple sheets of A4 outside regs and should never have been certified in the first place. It was even none compliant with regulations which were in force when the regulations were first agreed. Not the grey we managed to get the NG out before the grandfather regs were enforced type of regs more than likely it broke them as well though. We will have to wait and see if they produce a complete list of all changes.

The thing was none compliant should never have been flying. Now is it it Boeings fault or FAA fault for letting it fly? I really don't care and neither should pax. The system is broken and needs fixed.

 

[Alistair_Heaton]

Actually come to think of it there is a difference between centre of pressure and point of pressure.

centre of pressure is the local effect on the aerofoil as a unit and given in % of cord and perpendicular scaler value , and the point of pressure is a group of aerofoils combined together and can be a vector.

So the Centre of pressure for the max wing will not change from normal with AoA changes. The point of pressure for the system will change with the max because you have to add the centre of pressure of the wing to the centre of pressure of engine cowls lift giving a point of pressure which you can then use to work out your moments which need balanced by the trim stab.

 

[waross]

Early in this discussion there was a suggestion that at extreme angles of attack, the control force would go negative and beyond that AoA "hands off" would result in a continued increase in the AoA.
That post may have been in error.

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

 

[moon161]

Oh, I see what you want Dave-. A stable aircraft but non-compliant with FAA spec control forces because it's an MCAS delete. I agree without special knowledge as a pilot or working in a/c stability that that sounds at the very least, more predictable than MCAS, especially pre-disclosure. 'watch the new ones, stick sensitivity changes at high alpha', but then you're training pilots to fly wrt alpha instead of reference airspeeds, adding alpha guages to the cockpit display and so on. An aircraft isn't just something that flies, it a component of regularatory, logistical, economic and training systems, that's what this whole mess shines a light on.

 

[Alistair_Heaton]

They don't go negative if they did then the plane would be unstable and that'd definably a regs fail on civilian air transport aircraft.

The Canadians have actually brought up the idea that MCAS causes more problems than it solves. But there is no data when this affect actually starts occurring.
IS it at normal approach alphas or do you have to go to stupid extremes to get the effect. But after bringing it up and an article was posted here about it. Everything has gone silent on the subject.

The military fast jets do actually reference to the alpha. never seen it in the civilian world. Some unlimited aerobatic aircraft have alpha indications but i have never flown one of them. Way way to expensive.

 

[moon161]

Yeah, I listened to an interview of a french rafale pilot and he said instead of using corner air speeds as reference they used alpha and thrust setting I think. Above this alpha you're losing speed, below you're gaining. In retrospect, that's going to apply in the maneuvering regime instead of fast and level. As an engineering student, it seemed to be the best reference because it's what the wing cares about. If you're light and fast or slow and heavy, alpha will tell you how the lift curve and induced drag are.

 

[Alistair_Heaton]

I must admit I tend to agree with you.

But to convert every pilot in the world over to AoA would be rather painful. And to be honest its very rare outside the sim that we ever go over 30 deg bank and outside 20 nose pitch up attitudes and more than 10 degs nose pitch down. The fast jet pilots are pulling +G in all attitudes where the picture of the horizon bares very little relation to the aircrafts energy state and AoA.

 

[Alistair_Heaton]

There are two forms of artificial horizon out there.

It has been shall we say rather painful and deadly converting pilots between the two methods when they have been trained initially using one method.

I have flown aircraft with a Russian artificial horizon but very quickly it was screwing with my head even though i was looking out the window. It was a good learning experience.

After 5 mins I covered it up and only used the window and I certainly would never attempt to fly on instruments using it.

Its not so much an issue for none Russians because they will never have used it. But Russians converting onto western hardware such as Boeing or Airbus it must be a mind screw for years.

I believe these days young commercial pilots in Russia don't go near it.

 

[Alistair_Heaton]

just heard that the MAX product support world wide has been slashed. The UK and Ireland team has gone from 27 licensed techs down to 3.

When is the next stock market release by Boeing?

It seems that everything has to go through them, and not made public before. Something is going on but nothing said.

 

[dik]

From the news:

"The Federal Aviation Administration said on Monday that it is proposing requiring four key Boeing 737 MAX design changes to address safety issues seen in two crashes that killed 346 people and led to the plane's grounding in March 2019.

The agency is issuing a proposed airworthiness directive to require updated flight-control software, revised display-processing software to generate alerts, revising certain flight-crew operating procedures, and changing the routing of some wiring bundles."

We'll have to wait until the rest of the world receives these changes... It may be the Max is limited to US airspace...


Dik

 

[LittleInch]

Anybody fancy going through 90 odd pages???

https://www.faa.gov/news/media/attachments/737-MAX-RTS-Preliminary-Summary-v-1.pdf

Seems to be mainly MCAS software issues.

Discrepancy between sensors is 5.5 degrees allowable - seems a lot to me.

Section 6.6.has the wiring issue - No idea how much work is involved here??

A/P disconnects 1 second after stick shaker starts.

I love this bit - basically we don't have a requirement so the fact you can't turn the trim wheel is not relevant!! "Stabilizer Trim Wheel Forces comply with 14 CFR 25.143 by analysis per EASA CRI B-17
[highlight #FCE94F]because existing guidance does not cover stabilizer trim wheel forces[/highlight]

Doesn't talk much about what happens if MCAS is disabled, but is actually needed, other than "Reassessed aircraft stall characteristics with STS/MCAS and Electronic Feel Systems
inoperative and determined the aircraft meets FAA requirements" - So why is MCAS needed??

Nothing about the stick shaker disconnect / cancel.


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

 

[RVAmeche]

"Reassessed aircraft stall characteristics with STS/MCAS and Electronic Feel Systems
inoperative and determined the aircraft meets FAA requirements"

That is an odd statement...maybe the new software modifications mean the plane's handling isn't an issue without MCAS now?

Is it not weird that "Electronic Feel Systems" only appears in that one statement at the end?

 

[LittleInch]

It does say "stall characteristics", not pre-stall or high AoA, but is kind of flung in at the end.

I couldn't find anything really which addressed what happened if MCAS was inactive at these high AoA instances, but maybe it's buried in the report somewhere?

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

 

[Alistair_Heaton]

If they call it an anti stall system then they have no chance of getting it past certification. There is a whole raft of regs on that if it is.

AoA bounces around and depending on the gust and yaw there will be differences between the two sides. Although 5.5 degrees does seem rather a lot.

Seems they have a get out on the trim forces because no reg's cover it. And more than likely they can't do anything about them anyway.

The wiring changes on the machines in production won't be that hard to do. The ones already produced its a pretty major job. They can't leave dead wires in looms so will have to split the looms and then reform them. There will also have to be holes made/enlarged in pressure bulk heads for the new wire. Don't have a clue if they can get at said loom with out stripping out the interior or not.

The wording to me is that we have made Boeing do as much as they can with the design and we don't think they can do much more with it in any reasonable time frame. Next stage is start screwing around with the aerodynamics.

We shall see what the other regulators say about it.

I suspect we might be seeing it flying in the USA only for a couple of years.

 

[LittleInch]

The wording to me is that we have made Boeing do as much as they can with the design and we don't think they can do much more with it in any reasonable time frame.

... without junking the whole design and starting again.

There is still quite a lot for Boeing to do based on that document wrt crew alarms etc and coming up with a training package.

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

 

[Alistair_Heaton]

It's screwed in that regard it's still in the 60's.

It's a last of a kind Frankenstein.

Everyone knows if it doesn't fly again then Boeing commercial will go bust and screw the world.

To be honest over 50% the orders are gone anyway. They won't be able to dump them for cost price on the USA market even without including the initial design costs never mind the last 18 months.

You lot can fly on them if you like I won't be or the family. The mother in law won't know mind about the ban though

 

[LittleInch]

Some interesting divergence going on between regualtors

https://www.industryweek.com/leader...s-warn-of-europeus-split-on-boeing-max-return

https://www.bloomberg.com/news/videos/2019-09-05/aercap-ceo-on-aircraft-demand-boeing-737-max-video

from about 2 minutes on

This one makes the point that the FAA is saying they have fixed the faults on MCAS, but all the other things which have come out since are not being addressed.

https://www.aviationpros.com/aircra...es-its-plan-for-the-return-of-boeings-737-max

Reading the FAA document, I'm pretty sure that it says the MCAS only once action is reset once the AoA goes below some magic number. So if the AoA fluctuates about that number you could still get multiple actions of the stab (I think), though there may also be some sort of max deflection in total check.

All in all to not have a way to shut the system off from action and still be able to manually or as a separate system trim the stabiliser doesn't seem right to me. But what do I know?

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

 

[davefitz]

Perhaps an alternative solution, and opportunity, is to sell the max's to a third party re-manufacturer, who would modify the planes as required by all intl regulators, and rebrand them and then sell them to the airlines.They would need to be sold at a discount, determined by the market. Adding 2 more AoA sensors and adjusting the MCAS gain inversely by the square of the airspeed plus wiring changes etc would be included in the rebranding. The reason Boeing won't do this is likely becuase it would be an admission of negligence in the initial design process, and that legal issue dissapears in the rebranding.

The third party remanufacturer could be an LLc, formed of a conglomerate of various airline mfr's, such as boeing , airbus, China's CAC, and other partners.By spreading the reponsibility, it ensures intl regulator acceptance and also airline company acceptance.

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

 

[Alistair_Heaton]

You know just as much as the rest of us.

Common sense is being over ruled by interpretation and twisting of wording and fiddling of probability stats.

I suspect we will be still discussing what's going on this time next year.

I suspect the only way they will get everyone happy is by fitting smart probes which also measure AoA. But then they will be banging there heads against it not being a common type with the NG's