Boeing 737 Max8 Aircraft Crashes and Investigations [Part 8] 24

[Sparweb]

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

thread815-445840
thread815-450258
thread815-452000
thread815-454283
thread815-457125
thread815-461989
thread815-466401

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 from Ethiopia is now broken. See link from NTSB Investigations below)

Indonesian National Transportation Safety Committee preliminary report

NTSB Investigations

NTSB Safety Recommendation Report: Assumptions Used in the Safety Assessment Process and the
Effects of Multiple Alerts and Indications on Pilot Performance

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

Pulitzer Prize, For groundbreaking stories that exposed design flaws in the Boeing 737 MAX that led to two deadly crashes and revealed failures in government oversight.

http://www.sparweb.ca

 

[waross]

Do I understand that there just has to be a manual trim system, but there is no regulation saying that it has to be usable when it is really needed?
There are all sorts of justifications and reasons and arguments but at the end of the day, the more you need manual trim, the less likely that it will be possible to use.
Would a usable usable manual trim have significantly lowered the body count.
What would the late Dr. Richard Feynman have said if he had been part of the discussions?
I am sure that he would have asked some questions that could not be answered by the proponents of the existing manual trim system.

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

 

[LittleInch]

Waroos,

That's our interpretation of it - it turned out that there was no actual set down requirement for the amount of force required to turn the trim wheel or how many times you need to turn it to get 1 degree of movement. Hence the FAA can't make up a rule so are left with nothing to use to get Boeing to change anything. The diameter of the wheel apparently changed somewhere along the line, possibly into the NG to cope with changes to the cockpit layout which reduced the mechanical advantage. It apparently takes 15 turns of the wheel to make 1 degree of stab change. Now whether there is a requirement for a manual system or just some level of independent back up I don't know. I don't know what the airbus set up is for the stabiliser, but I think it's similar. The 737 apparently had back up motors at one time but they got removed in later versions.

I think the answer to the "Would a .." is most definitely Yes, at least for the second crash. The poor Ethiopian pilots apparently tried to move the stab manually after they disabled the trim motor, but couldn't move it, not helped by their high speed. That's why they turned the trim motors back on and then plummeted into the ground. Only one pilot could try this as the other was holding the plane just about horizontal with both hands. Later on the "roller coaster" method was noted as being removed from the manual which released some of the tension on the stab in a dive before you pulled up and then tried again.



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

 

[dik]

#3, will be more interesting, with what has happened.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Alistair_Heaton]

I am pretty sure but not 100% that the airbus trim is operated by a backup hydraulic system which is powered off an emergency bus.

The main system has 3 electric motors and then the 4th backup system which has multiple electrical power sources. I think the only thing which doesn't have more than three backup methods is the actual main screw jack itself. But as the elevators are hydraulically powered with 3000 psi and there is 3 hydraulic system which power them as well even if the stab becomes locked you can still move the elevator and fly it.

The only way they get away with FBW is by having at least triple of everything that's involved in primary safety. The new generation of FBW goes even further. the A220 has 6 AoA sensors. But I might add we still don't have an AoA indication on the instruments in the cockpit.

The issues is that the 737 is now FBW with computer inputs into the primary flight controls but has none of the required FBW backups. Which is one of the reasons why I think they had a limit of how far they could push them to change things without scrapping every single aircraft that they had already produced.

 

[Alistair_Heaton]

EASA has released its requirements.

https://ad.easa.europa.eu/ad/20-184

They have also set a load of limits to perform low viz and autolands and also coupled RNP approaches . Which may cause Ryanair no end of problems.

But the big thing is the

Foreign AD: Federal Aviation Administration (FAA) AD 2020-24-02 dated 20 November 2020,which is not adopted by EASA.

Which is to be honest the most worrying aspect.

 

[Sparweb]

Yes, they have a few special features in their proposed new AD that the FAA didn't address.

Looks like the circuit breakers for the stick-shaker need to be found in a hurry, so the normal procedure for this will become "pull the breaker". This is the kind of procedure that systems design has been working AWAY FROM for 50 years. I bet Transport Canada will get on board with this strategy too, given some of the other things they've said in the past few months.

So I have to wonder, now, if the reliability level has been "rounded down" from the required 10^^-9 to... maybe 10^^-8.9. And stay out of the operations where you really depend on both high functionality and reliability at the same time (RNP for example). And everyone is just going to put up with it for now, maybe hoping that a more long-term fix can be finished a year or so from now. Proper DAL is not whipped into black boxes like magic, or overnight.

Does that cover all the holes in the swiss-cheese?

http://www.sparweb.ca

 

[Alistair_Heaton]

There are more than a few QRH cards on the 737 that require CB pulls. The question is will this one need 1.5 meter long arms or get out your seat or not.

I don't really understand what the problem is with the RNP stuff. Its all pumped through the same flight director logic as the ILS coupling. The fancy stuff is all done in the box of tricks doing error calculations and using the SBAS to get the high resolution both horizontally and vertically.

But issues like this are not for stick monkeys like me to be worrying about.

And it definitely won't and can't cover all the holes in the swiss cheese. There are still holes there from the initial 1960's design that have never been fixed.

 

[davefitz]

So, after a year of not flying passenger jets, do the skills of the average pilot get a bit rusty?

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

 

[Alistair_Heaton]

Hell yes you can feel it after 2 weeks vacation.

I am feeling rusty flying 30 hours a month.

They will go to the SIM first but you don't get in the groove until your banging in 8-12 approaches a week.

 

[Sparweb]

I don't really understand what the problem is with the RNP stuff. Its all pumped through the same flight director logic as the ILS coupling. The fancy stuff is all done in the box of tricks doing error calculations and using the SBAS to get the high resolution both horizontally and vertically.

I bet inside that box there is too much reliance on the same AOA vanes that got us into this mess. Sure you can correct it with the GPS but it's a correction of +/- applied to another number that's gone full-scale wacky. If the system still doesn't have the power of voting down the bad data...

http://www.sparweb.ca

 

[Alistair_Heaton]

As such it just provides a heading or a vertical speed to the flight director which the autopilot then gives control input instructions to a set of servo's to adjust the relevant controls. It will use the same screjack motor as everything else does to control pitch.

There is no flight envelope protection on that side of things if it try's to do something stupid it will take the aircraft to the stick shaker. Which might be the reason, there was an issue with the stick shaker running and the autopilot not kicking out. Which wouldn't be fun at 100ft and the ground not insight a a go-around would involve the aircraft touching the runway.

 

[JohnRBaker]

Note that American Airlines flew their first 737MAX flight today since the grounding, with albeit non-paying customers, but for the first time, they were not American Airlines people. In this case, it was a group of reporters which were flown from Dallas to Tulsa. It appears that they will soon be making revenue generating flights. Delta and Southwest are expected to follow suit.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[Alistair_Heaton]

What's your feeling for general feeling about the MAX your side of the pond?

To be honest there is that little flying going on in Europe and Norwegian is utterly screwed. In fact I think the court case with Boeing is due to start soon over several billion dollars. Even if it was released to fly it wouldn't be in the air anyway

I am flying around with loads that would be poor in a Q400 never mind a A220.

I expect that most pax wouldn't know the difference between and Boeing and an airbus and if the safety card didn't mention the model then they wouldn't have a clue what they were on.

 

[waross]

I expect that most pax wouldn't know the difference between and Boeing and an airbus and if the safety card didn't mention the model then they wouldn't have a clue what they were on.

An other possible issue may be rebranding.
Even if Boeing doesn't re-name the Max, there may be a suspicion that some airlines may rename the Max.
Then there is equipment substitution; the craft listed in the booking information may be substituted with a Max without notice.
With that in mind, and with a healthy distrust of Boeing, some of us will be avoiding flying with carriers with Boeing fleets of any flavour.

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

 

[Alistair_Heaton]

Commercial pressure is starting with Airbus now with the A220 Air France is trying to get Airbus to stretch the A220-300 already and its only been flying for a few years.

They prefer it to the A320 NEO. And to be honest I don't blame them. The airbus FBW is decades old now and clunky compared to the Canadian product.

Seems like Ryanair have ordered another 75 737-MAX-8200 but to my knowledge its not even certified yet for the additional pax numbers which require another emergency exit

 

[davefitz]

Whatever happened to the ryanair proposals to fly with only 1 pilot + 1 stewardess, passengers will have to stand, and pay to use the toilet?

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

 

[Alistair_Heaton]

That's just his normal bluster to get free advertising. He usually comes out with something every 6 months to get social media excited.

I hope they put the video public of the pax evacuation tests with 197 pax trying to get out with only 50% of the doors working and no wing slides in 90 seconds.

 

[Alistair_Heaton]

At least the new jets won't be stinking of pee and poo after a week flying

https://www.buzzfeednews.com/article/tasneemnashrulla/emotional-support-animals-airlines-new-rule

 

[davefitz]

I recall one of the evac tests ( in 1975) where they recruited 197 college athletes to act as the passsengers, priming them for the fast reaction requirements , and of course they passed the 90 sec test. I guess they do not recruit patients from nursing homes to be the test passengers.I wonder how fast the evac is when half the passengers have dogs and miniature horses as their "comfort pets" .

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

 

[LittleInch]

I'm sure one of the trials / tests they did to re enact a poor real evacuation was to offer cash incentives to the first 50 people off the plane, regardless of where you were sitting to replicate the panic that could ensue in a fire / smoke situation.

They discovered that the narrow gap in the aisle due to the galley caused a log jam of people, but not before there were a few broken bones and sprains as people vaulted over seats and basically forced themselves to the front of the queue. And that was a 737.

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