Boeing 737 Max8 Aircraft Crashes and Investigations [Part 2] 44

[Alistair_Heaton]

This thread is a continuation of:

thread815-445840


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Another 737 max has crashed during departure in Ethiopia.

To note the data in the picture is intally ground 0 then when airborne is GPS altitude above MSL. The airport is extremely high.

The debris is extremely compact and the fuel burned, they reckon it was 400knts plus when it hit the ground.

Here is the radar24 data pulled from there local site.

It's already being discussed if was another AoA issue with the MCAS system for stall protection.

I will let you make your own conclusions.

 

[RVAmeche]

Agreed, commercial aviation should be one of the most risk-adverse fields out there. There have been two crashes, of the same make/model, relatively soon after the model was released. I would think that's enough justification to put them on the ground and see what's going on and determine what (if anything) needs to be addressed.

 

[Pud]

Looks like the French are going to look at the flight recorders:

http://uk.reuters.com/article/uk-et...ines-flight-recorders-spokesman-idUKKCN1QU2TR

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[zeusfaber]

...and that Boeing is now putting a worldwide grounding in place (though with an FAA ban in place and no access to any of the major worldwide hubs, this could be a case of bowing to the inevitable).

A.

 

[thebard3]

At any rate, I think a simple risk matrix can be used to support a grounding, even with as little as we know. Two brand new Max 8 apparently fly themselves into the terrain on a clear day with experienced pilots reporting control issues, killing all souls on board. That weighs heavy on the consequence side of the equation even if the probability is low or non-existent for most of the 300+ planes in the fleet.

I sort of agree, but regarding the previous crash, I have a hard time blaming the aircraft design although it seems the MCAS was perhaps a contributor. It flew several previous flights with a known hardware issue that was never properly repaired. Also, there is an assumption that this crash is somehow related to the first, although as far as we know here there is no evidence yet to support that. Assuming they are related to the MCAS, new aircraft always require some type of in service modification/improvement just like anything else. I guess you just hope that an issue like this would be identified and corrected without people losing their lives.

Brad Waybright

It's all okay as long as it's okay.

 

[thebard3]

Agreed, commercial aviation should be one of the most risk-adverse fields out there. There have been two crashes, of the same make/model, relatively soon after the model was released. I would think that's enough justification to put them on the ground and see what's going on and determine what (if anything) needs to be addressed.

I wish I had just said that instead.

Brad Waybright

It's all okay as long as it's okay.

 

[MacGyverS2000]

Caught a glimpse of the Ethiopian crash site on the local news... it showed a bulldozer pushing large masses of scrap metal into even larger masses. Someone please tell me they're not making the site more "tidy" by using a bulldozer. I thought immediate course of action was to collect all pieces of the aircraft and reconstruct in a local hangar, making careful note of where each piece was found.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[LittleInch]

I agree it doesn't look like a very "secure" site, but the level of destruction is unreal, it all basically buried itself several metres down in what is apparently quite soft ground out there having gone in near vertical by the look of things.

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

 

[RoopinderTara]

Apparently there is a way to turn off the MCAS with a switch in the console between the pilots. Can anybody verify this with a picture? I'd like to update our article (below) with that information.

From my research for the article, I found that not all pilots were informed of the MCAS or the cut off switch. The head of one pilots union said words to the effect of "Why should they know? I don't know how my TV works."

https://www.engineering.com/Electro...a-May-Have-Caused-Boeing-737-MAX-Crashes.aspx

Roopinder Tara
Director of Content
ENGINEERING.com

 

[waross]

From the discussion of the Lion Air crash it appears that every time the pilots turned the system off, it turned itself back on.

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

 

[LittleInch]

Roopinder,

See this which is the best diagram and photo I've ever seen on the lion Air crash.

https://www.nytimes.com/interactive/2018/11/16/world/asia/lion-air-crash-cockpit.html

I still think they are talking about the STAB TRIM CUTOUT switches in the centre console below the throttle levers.

The manual trim switches on the yoke can override the trim position but only for a few seconds.

Now how you manage to flick the safety covers out the way and flick those switches down while the plane is going haywire and bouncing around is another thing. Also you need to do both at the same time by the look of it (can a pilot confirm this?)

If you only manage one and then the system kicks in I can only imagine one trim going one way while the other stays put won't be good.





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

 

[LionelHutz]

Apparently there is a way to turn off the MCAS with a switch in the console between the pilots. Can anybody verify this with a picture? I'd like to update our article (below) with that information.

It was already posted by SparWeb. This link has a picture.

http://www.b737.org.uk/mcas.htm

However, the switches don't disable the MCAS, they disable the motor operating the stabilizer. Then, the pilots have to manually control it.

 

[Spartan5]

Caught a glimpse of the Ethiopian crash site on the local news... it showed a bulldozer pushing large masses of scrap metal into even larger masses. Someone please tell me they're not making the site more "tidy" by using a bulldozer. I thought immediate course of action was to collect all pieces of the aircraft and reconstruct in a local hangar, making careful note of where each piece was found.

As he spoke, a bulldozer dumped more debris from the plane into a huge pile in front of the assembled mourners, while men wearing white masks and carrying plastic bags picked through the dirt.

The plane plowed nose down into the earth, and much of the wreckage was buried at least 60 feet deep, said Zhang Jun, a construction engineer working at the site.

He brought his back hoe and bulldozer from Addis Ababa, where he was working on an airport construction project.

“It is in the soil very deep,” he said of the aircraft debris. “The pieces are very small, no more than two meters [about 6 ½ feet] long, he said. The human remains he found, he added, “were even smaller.”

https://www.washingtonpost.com/worl...aa9c2a-4659-11e9-8aab-95b8d80a1e4f_story.html

 

[itsmoked]

This 'buried in the dirt' has me wondering how they found the Boxes so quickly.. Oh wait, they're now in the tail aren't they?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[IRstuff]

And, they beep.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

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[Pud]

Grounded until May at least:

http://www.bbc.co.uk/news/business-47567039

Cheers

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

 

[MDEAus]

The Stab trim cutout switches are inline one is a backup in case the first one fails closed. flipping one should still cut power to the motor but for safety sake it's a redundant pair that gets flipped at the same time. In the closed position it has protection from being moved to cutout accidentally. Once moved to Cutout all electric trim is lost, pilots can only manually trim the plane. The pilots electric trim on the stick stops MCAS for 5 seconds after release before it re-initiates trimming (runaway trim is apparently different in that the pilots electric trim switch does nothing to stop it and can be up or down). MCAS can not turn itself back on after stab trim cutout switches are moved to cutout, only after being stopped momentarily by the pilots trim switch(5s before reactivation).

I think from pictures of the crash site it is clear it was a high speed nose down crash, and that rules out any mid air explosion or engine failure. There is a very concentrated debris field around the crater, not a large extended debris field cover kilometers before the crash. Any sort of mid air explosion the was significant enough to cause a high speed nose down crash would have left a secondary debris field.

The FDR and CVR data can not come out soon enough but I will wait patiently.

 

[Sparweb]

I am still struggling with the purpose of the MCAS.

This new location and size of the nacelle causes it to produce lift at high AoA; as the nacelle is ahead of the CofG this causes a pitch-up effect which could in turn further increase the AoA and send the aircraft closer towards the stall. MCAS was therefore introduced to give an automatic nose down stabilizer input during steep turns with elevated load factors (high AoA) and during flaps up flight at airspeeds approaching stall.

What I get from that is the MCAS is most active during take-off and climb-out (the times of both crashes). It should be inert and/or remove all compensation during cruise and descent for landing. Right so far?

Also, there seems to be a variable lift-curve on the nacelle body, possibly energized by the intake's airflow. What doesn't pass into the nacelle is accelerated before passing over the nacelle body, generating lift on that surface. Takeoff and climb are the high-power phases of flight, too, so the acceleration would be greatest.
One more thing: none of the descriptions of the MCAS system refer to an engine power as an input value, just AoA airspeed and altitude.

The MCAS function becomes active when the airplane Angle of Attack exceeds a threshold based on airspeed and altitude.

Lion Air crashed into the ocean (alitude=0) and Addis Ababa is at 7,700 feet so we have a wide spread of altitude inputs with the same result.
What is common in both crash events is that the airspeed and angle of attack were all over the place.

Would it help if we thought in terms of a PID controller that is not properly tuned, leading to an overshoot? The literature (in the media; I haven't been able to read Boeing's data) says that the rate is 2.7 (correction: 0.27) degrees per second. So there's no way to tune the rate to keep up with more rapid pilot inputs or gusts? Making it not even a "P" controller (Proportional)?
Or is this a wrong-headed way of thinking about this system's function?

<edited to fix an incorrect number, thank you LH>
No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[waross]

LittleInch and MDEAus; Thanks for the clarification.

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

 

[Alistair_Heaton]

Rumours are going around that they found the elevator screw Jack and it was in the fully nose pitch down position.

 

[LittleInch]

Oh,

The thing I haven't figured out is what happened apparently at the end of the Lion air flight, i.e. it bounces around seemingly between the application of the MCAS and recovery in a cycle of several seconds and then after some time it just dives near vertical.

Does the MCAS gradually increase the max trim angle?
Does it allow a certain number of cycles and then go beserk and just goes max nose down?
If you don't pull the elevator trim back to level does it go a second time after a few seconds for another attempt at nose down until it runs out of elevator trim?

Sparweb, from what I've heard the trim control goes at a certain increase angle per second to a max of 2.7 degrees after I think 9 seconds.



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