737 Max

[Charles Darwin]

Fast forward to 5:27

YouTube

[6L6]

I fly jets for a living. They are incredibly complex machines that have so many rules and regulations around them it's mind boggling. I've been studying this problem with the information I can find, and having multiple daily discussions with 3 pilots whom are very good friends and fly the Max. We're getting into the very nether reaches of flight control rules and stability requirements and discussing the type of things that almost never come up outside of the flight test community.

Here's what we know for sure....


















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Get the point?

The FDR and CVR have only been gotten to a place for analysis in the last 24hr. That data will have to be reconstructed and analyzed, and that will take time. There is basically nothing known about the Ethiopian crash at this time, aside from some rudimentary radar track information.






So.



Here's what you should do in the meantime, if you want to have any chance of understanding where the conversation is almost certainly going to head in the next few months - Read up on aircraft dynamic stability, static stability, positive stick force gradient, changes in stick force with changes of center of gravity, and stability at various power settings. The MCAS is a certified solution to address issues in these areas. (which are normally done with the feel computer, but this needed a bit more than that)

I suspect there's an error in how it interfaces with the aircraft, and things are pointing to a single point of failure that messes up the system somehow. I.E., the MCAS is getting bad info and makes erroneous changes to "fix" something that's not happening.


It would take me a couple hours to write the pages necessary to explain in a way that might be understandable by someone who has never flown, because we're talking about the most fundamental 'feel' of an airplane - which is to say that airplanes fly like airplanes because it's very specifically engineered to feel a certain way and react a certain way if you are within the standard flight envelope, and if it doesn't, it can't pass certification.

Anyway, the media gets about 90% of anything relating to aircraft just plain wrong. Have you ever seen a news clip on something in your profession? How much of it did they get correct? See what I mean?

[chrisb]

Is there much credence to be put into things that I’ve read that imply this particular model has different aerodynamics -I guess you’d call it “feel” - than the numerous other models of the 737 family on which the bulk of pilots will have had their sometimes tens of thousands of hours of experience? That compounded with a Maneuvering Characteristics Augmentation System receiving erroneous sensor input could make for -well, I guess we’ve seen. Starting to look like Boeing and the FAA have some work cut out for them.

[6L6]

Originally Posted by chrisb

Is there much credence to be put into things that I’ve read that imply this particular model has different aerodynamics

Yes.

-I guess you’d call it “feel” - than the numerous other models of the 737 family on which the bulk of pilots will have had their sometimes tens of thousands of hours of experience?

Feel is related to aerodynamics and also shaped in response to it. interrelated for sure.

Again, the Ethiopian crash still has essentially no information known around it and everything is speculation at this point. Let's talk when there is real information known.

[KaffiMann]

Originally Posted by Charles Darwin

Fast forward to 5:27

YouTube

I do not fly jets for a living, but this seems very relevant. Important details on the new implemented functions. I think that if Boeing starts blaming this on pilot training, they'd run into trouble quick. Seems they implemented changes to the auto correction system that can potentially completely over ride most actions from the pilots.

[Charles Darwin]

I find it worrying that according to that pilot in the link Boeing said that the Max behaves exactly like previous 737 models, no further training would be needed and that pilots did not even know that MCAS existed until the Lion Air crash.

Meanwhile more and more reports of difficulties to to control the Max 8 surface from all over the world including US and Dutch pilots.

[avtech23]

Here's what we know for sure....

+1 for everything 6L6 said. Thanks, you saved me a lot of typing!

Is there much credence to be put into things that I’ve read that imply this particular model has different aerodynamics

Yes. The stability of an aircraft in flight depends on a delicate balance of mass-moment as well as parasitic elements, aerodynamic shapes etc. The CFM Leap engines on the Max have larger nacelles and are placed further forward than on the 737-800 for example. This (apparently) made the handling profile different compared to the other 737 models. Think of how steering and suspension geometry affects a race car handling. To combat the instability at high angles of attack (the angle of relative airflow on the aerofoil) computer augmentation can be used to keep the aircraft in the safe operating areas (think traction/stability control in cars).

There is an article here that explains it quite well to save me some typing:

Boeing’s automatic trim for the 737 MAX was not disclosed to the Pilots - Leeham News and Analysis

Until the NTSB reports are published, there can only be armchair speculation which is often upsetting to the families of loved ones searching for answers.

[Charles Darwin]

Originally Posted by KaffiMann

I think that if Boeing starts blaming this on pilot training, they'd run into trouble quick.

The Lion Air crash was ultimately blamed on shoddy maintenance by a second rate charter airline which led to a faulty sensor.
At least that was strongly implied if not the official result.

This doesn't really work for Ethiopian as their practices are widely recognized as impeccable.

It'll be interesting what the flight recorder data comes up with. However I am also disturbed by the strong worded insistence that the recorders must be analyzed in the US. Luckily they went to Paris for analysis.

[Bonsai]

There was a piece on the BBC that showed the flight patterns (speed and altitude) for both the Lion Air and the Ethiopian Air MAX 737's from take off to crashing (about 5 minutes or so IIRC). Both show airspeed all over the place and huge changes in altitude. In the Ethiopian Air case, it dropped over 1000 feet in about a 10 second window before climbing again.

I've flown hundreds of times all over the world - I cannot imagine what those flights must have been like.

As 6L6 says - we will not know until the data has been analysed in full. As electronics guys, we know squat about aerodynamics at this complexity level.

[traderbam]

I am not a pilot. I do wonder if real pilots think pilot error could explain the erratic behaviour and sudden nose dive to the ground (albeit if a sensor was faulty). My engineering background makes me suspicious of the plane not obeying the pilots. Boeing has emphatically denied allegations that the planes are unsafe.