Ethiopian Airlines plane crashes on way to Nairobi

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by mnmodels » Thu Mar 14, 2019 4:17 pm

Thank you.

So all systems are integrated to a single electric hydrolic actuator controlling a jack screw to change the angle of stab....

Even more scary than i thought. So no redundancy build into system? No man can overpower that system!

If it lock in a bad position -nothing will fix it. This system was and is working flawless for decades until another system was integrated with this single actuator....

rgds
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Fransw » Thu Mar 14, 2019 4:17 pm

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chartoftheday_17354_boeing_aircraft_deliveries_n.jpg
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by JCO7 » Thu Mar 14, 2019 4:25 pm

jimdavis wrote:
Thu Mar 14, 2019 3:27 pm

It is hugely powerful and there is no way that the elevator will overcome it if it runs away to one of its extremes.

jim
The aircraft is supposed to be flyable on elevator only, regardless of stab position.

From Max 8 QRH (Stabiliser Trim Inoperative):
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Thu Mar 14, 2019 4:26 pm

mnmodels wrote:
Thu Mar 14, 2019 4:17 pm
Thank you.

So all systems are integrated to a single electric hydrolic actuator controlling a jack screw to change the angle of stab....

Even more scary than i thought. So no redundancy build into system? No man can overpower that system!

If it lock in a bad position -nothing will fix it. This system was and is working flawless for decades until another system was integrated with this single actuator....

rgds
Grabbed from https://www.airliners.net/forum/viewtop ... start=1800 :
eIPESaX.jpg
As you can see, there is a manual (mechanical) cable connection directly from the jackscrew to the cockpit (big wheel at the pilot's knee). The actuator motor is designed so that it can never produce enough torque that the pilot can not overpower it with relative ease.

EDIT: Note that nothing here changed on the MAX series. MCAS is only software on the flight computer, and uses the existing autopilot trim output to the actuator.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by mnmodels » Thu Mar 14, 2019 4:41 pm

Justin,

"The actuator motor is designed so that it can never produce enough torque that the pilot can not overpower it with relative ease"

If this is true - then stab trim did not crash the 737.....a co pilot with 200 hours can hold the wheel and the captain can fly the plane back to airport regardless of computers.... after all it is a Boeing fly by wire....

The plane was pitching up and down - like a loose jackscrew effect....

Or am i missing something...
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by JCO7 » Thu Mar 14, 2019 4:50 pm

mnmodels wrote:
Thu Mar 14, 2019 4:41 pm
Justin,

"The actuator motor is designed so that it can never produce enough torque that the pilot can not overpower it with relative ease"

If this is true - then stab trim did not crash the 737.....a co pilot with 200 hours can hold the wheel and the captain can fly the plane back to airport regardless of computers.... after all it is a Boeing fly by wire....

The plane was pitching up and down - like a loose jackscrew effect....

Or am i missing something...
The oscillations in altitude would be caused by intermittent activation of MCAS in trimming the aircraft nose down, followed by pilot reacting with pitch and trim to correct, followed by MCAS trimming nose down again - an on-going battle between the pilot and the MCAS. Once the trim cutout switches are moved to cutout MCAS can no longer trim and the aircraft can be flown using manual trim.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jvdl » Thu Mar 14, 2019 5:00 pm

Interesting article by a former NTSB chairman: https://www.nytimes.com/2019/03/13/opin ... unded.html

Bolded font by me, not the NYT.
A new-model airliner crashes, killing all 189 people aboard. Less than five months later, another airliner of the same new model crashes, killing all 157 aboard. Both seem to have occurred under similar circumstances. The world was understandably terrified, and until Wednesday, the United States Federal Aviation Administration stood alone as the only major aviation safety agency that had not ordered the grounding of this airline model, Boeing’s 737 Max 8.

President Trump’s executive order on Wednesday afternoon to ground all Boeing 737 Max 8s was a necessary step. But it is a step that should have been taken directly by the federal agency responsible for aviation safety. That it came from the White House instead speaks to a profound crisis of public confidence in the F.A.A.

The roots of this crisis can be found in a major change the agency instituted in its regulatory responsibility in 2005. Rather than naming and supervising its own “designated airworthiness representatives,” the agency decided to allow Boeing and other manufacturers who qualified under the revised procedures to select their own employees to certify the safety of their aircraft. In justifying this change, the agency said at the time that it would save the aviation industry about $25 billion from 2006 to 2015. Therefore, the manufacturer is providing safety oversight of itself. This is a worrying move toward industry self-certification.

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Thu Mar 14, 2019 5:03 pm

mnmodels wrote:
Thu Mar 14, 2019 4:41 pm
Justin,

"The actuator motor is designed so that it can never produce enough torque that the pilot can not overpower it with relative ease"

If this is true - then stab trim did not crash the 737.....a co pilot with 200 hours can hold the wheel and the captain can fly the plane back to airport regardless of computers.... after all it is a Boeing fly by wire....

The plane was pitching up and down - like a loose jackscrew effect....

Or am i missing something...
Now that is the interesting bit. Calculating G loads from FR24 data, it looks like some of the pitch events resulted in +/- 2G excursions (although the majority of the flight was <|0.5G|). So the G loads should not have been enough to seriously inhibit the pilots.

So, either it is a spectacularly mismanaged trim runaway (MCAS or otherwise), or something else went wrong.

The mechanics of the control system are identical (as far as I can find out) to the NG, so there are millions of flight hours without any issues.

No idea what else it could be?
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by JCO7 » Thu Mar 14, 2019 5:20 pm

heisan wrote:
Thu Mar 14, 2019 5:03 pm
mnmodels wrote:
Thu Mar 14, 2019 4:41 pm
Justin,

"The actuator motor is designed so that it can never produce enough torque that the pilot can not overpower it with relative ease"

If this is true - then stab trim did not crash the 737.....a co pilot with 200 hours can hold the wheel and the captain can fly the plane back to airport regardless of computers.... after all it is a Boeing fly by wire....

The plane was pitching up and down - like a loose jackscrew effect....

Or am i missing something...
Now that is the interesting bit. Calculating G loads from FR24 data, it looks like some of the pitch events resulted in +/- 2G excursions (although the majority of the flight was <|0.5G|). So the G loads should not have been enough to seriously inhibit the pilots.

So, either it is a spectacularly mismanaged trim runaway (MCAS or otherwise), or something else went wrong.

The mechanics of the control system are identical (as far as I can find out) to the NG, so there are millions of flight hours without any issues.

No idea what else it could be?
Just bear in mind that an erroneous AoA input would have caused unreliable airspeed and probably stick shaker activation. This would have been the pilots' primary focus. Then MCAS subtly trims in the background, creating a horribly out of trim condition. The pilot could have even lowered the nose himself initially to recover from the non-existent stall. You now have a nose down attitude with excessive nose down trim being applied without your knowledge.

You may then realise the aircraft is not actually stalling and attempt to bring the attitude and thrust toward the Airspeed Unreliable recovery settings (4 degrees nose up/75% N1) but you require large elevator and trim inputs to achieve this. Just as you start getting control the MCAS activates again and continues to trim nose down. You are faced with erroneous speed indications, stick shaker activated and struggling to control the aircraft in pitch.

The only way out is to timeously move the stab trim switches to cutout, IF you realise under the stress of the situation that there is uncommanded trim being applied.

All easier said than done.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jimdavis » Thu Mar 14, 2019 5:39 pm

JCO7 wrote:
Thu Mar 14, 2019 4:25 pm
jimdavis wrote:
Thu Mar 14, 2019 3:27 pm

It is hugely powerful and there is no way that the elevator will overcome it if it runs away to one of its extremes.

jim
The aircraft is supposed to be flyable on elevator only, regardless of stab position.

From Max 8 QRH (Stabiliser Trim Inoperative):
Thanks so much JCO7. My info came from a current airline captain, but if the QRH says otherwise - so be it! We live and learn. :D

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Bushpilotzaa » Thu Mar 14, 2019 5:45 pm

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jimdavis » Thu Mar 14, 2019 5:52 pm

JCO7 wrote:
Thu Mar 14, 2019 5:20 pm

Now that is the interesting bit. Calculating G loads from FR24 data, it looks like some of the pitch events resulted in +/- 2G excursions (although the majority of the flight was <|0.5G|). So the G loads should not have been enough to seriously inhibit the pilots.

So, either it is a spectacularly mismanaged trim runaway (MCAS or otherwise), or something else went wrong.

The mechanics of the control system are identical (as far as I can find out) to the NG, so there are millions of flight hours without any issues.

No idea what else it could be?
Just bear in mind that an erroneous AoA input would have caused unreliable airspeed and probably stick shaker activation. This would have been the pilots' primary focus. Then MCAS subtly trims in the background, creating a horribly out of trim condition. The pilot could have even lowered the nose himself initially to recover from the non-existent stall. You now have a nose down attitude with excessive nose down trim being applied without your knowledge.

You may then realise the aircraft is not actually stalling and attempt to bring the attitude and thrust toward the Airspeed Unreliable recovery settings (4 degrees nose up/75% N1) but you require large elevator and trim inputs to achieve this. Just as you start getting control the MCAS activates again and continues to trim nose down. You are faced with erroneous speed indications, stick shaker activated and struggling to control the aircraft in pitch.

The only way out is to timeously move the stab trim switches to cutout, IF you realise under the stress of the situation that there is uncommanded trim being applied.

All easier said than done.
[/quote]

Very interesting JCO7. Do you think that crew would, in desperation, look outside and try to fly visually? Also could the attitude indicator have been effected by erroneous inputs form the pitot or AoA sensors? Would it not have been instinctive for the crew to resort to basic power and attitude flying?

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by mnmodels » Thu Mar 14, 2019 5:55 pm

Thank you for making me understand...

My conclusion (if no other structual faults are found) is then that the 8000hr pilot was managing systems instead of looking out the window and flying the aircraft because the co pilot was not as expereinced. It was clear skies and cavok.

He should tell the diff between 200knts and 400knts by looking out the window 4000ft up....

As said before - easier said than done....the hudson river come to mind....

Rgds
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by JohnMagee » Thu Mar 14, 2019 6:05 pm

According to an article dd 29 Nov 2018: Southwest is adding new angle of attack indicators to its 737 max fleet. "The AOA indicator will provide a valuable supplemental cross-check in the event there is an erroneous AOA signal present"

https://theaircurrent.com/aviation-safe ... max-fleet/
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by biffvj » Thu Mar 14, 2019 6:07 pm

bucky_za wrote:
Thu Mar 14, 2019 2:21 pm

What is the possibility AirET managed to shut down the system as directed by Boeing after the previous crash,
and after regaining control our 8000 hour Pilot pulled up out of the dive, using dive recovery techniques no doubt practiced in the sim,
only to be caught out by the new pitch up characteristic on the MAX ending up in a stall that the MCAS is designed to prevent.

The various tracks as posted of the Altitude/Vspeed etc all show a big jump in altitude before going of Radar.
Looks like it.
The first holes in the cheese are built in to the MAX. MCAS on and with incorrect sensor inputs: nose down problem. MCAS off and plane does not fly properly. Tie that in with aircrew not realizing what is actually happening in the short time they have to recover.

BTW: Notice how similar the Boeing share price curve tracks the flight paths of both planes that went down.
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