Ethiopian Airlines plane crashes on way to Nairobi

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Stephan van Tonder
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Stephan van Tonder » Fri Mar 15, 2019 9:05 am

Ugly Duckling wrote:
Fri Mar 15, 2019 7:48 am
A long read. It details the reports filed on the NASA ASRS or Aviation Safety Reporting System.
https://www.theatlantic.com/notes/2019/ ... ax/584791/
What is interesting there are two identical reports of airplanes starting to sink immediately after engaging autopilot, which is suposedly something that will disable mcas. So are we looking at some other undocumented feature not yet discovered? Both of those had fairly strong crosswind during take off.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Volo » Fri Mar 15, 2019 9:11 am

The elevator trim runs independently from the Stabilizer trim which is controlled by the Jack screw . It follows that if the Jack screw winds the Stabilizer to produce a nose down force ,It can be countermanded by the elevator trim until it runs out of authority and is overpowered by the Jackscrew. That's when the aircraft noses down irretrievably unless the jackscrew is reversed but that seemingly takes too long either hydraulically or manually to bring the nose up again . This also explains why it could be repeatedly re trimmed as much as 24 times as in the LionAir accident .
There was a report that the Ethiopian accident aircrafts Jackscrew was found and there was evidence of the Jackscrew having telltale evidence of negative stabilizer deflection.
A common thread in these accidents appears to be incorrect airspeed as the primary trigger in the accident sequences - just my opinion.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Stephan van Tonder » Fri Mar 15, 2019 9:45 am

there is only one trim system and that is that is the stabilizer (using the jackscrew). It is either wound manually by drum and cable via the trim wheel or electrically by motor (which apparently can be / should be able to be overpowered by hand)
Justin had a diagram of it earlier. There is no separate trim system that activates on the elevator.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Spoke Eagle » Fri Mar 15, 2019 10:19 am

Shurely MCAS is not to blame? One of the Spook pilots is getting airspeed warnings and keeps on accelerating the aircraft. At the same time it gives MCAS speed warnings which keeps on trimming down until the pilots cant hold her anymore. It must be a Spook that works off airspeed telling the others to react.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Volo » Fri Mar 15, 2019 11:15 am

http://aviationweek.com/site-files/avia ... jillas.jpg

Image of MAX 8 elevator and trim tab
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Volo » Fri Mar 15, 2019 11:20 am

https://encrypted-tbn0.gstatic.com/imag ... 7Hpc-JBRoQ

This image calls it a balance tab as opposed to a trim tab - so I think this is normally not adjustable as in a trim tab
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Stephan van Tonder » Fri Mar 15, 2019 11:26 am

http://code7700.com/aero_balance_tabs.htm

https://www.pmdgsim.com/2016/10/why-doe ... 37_21.html

Yes balance tabs which assists in control forces during hydraulic system failure. It is not a trim system actuated during flight.
I know there is also some sort of hydraulic linking of then these days so that during flap activation they become an anti balance tab. Just can't find that right now.

Edit - this is a good description. That was for 737 Ng but 'should' also apply to max.

source here: https://www.slideshare.net/theoryce/b73 ... t-controls


Elevator Tab Control Mechanism The elevator tab mechanism changes the function of the elevator tab. When the TE flaps are up, the elevator tab operates in the balance mode. When the TE flaps are not up, the elevator tab operates in the anti-balance mode which aids nose up control with the flaps not up. The elevator tab control mechanism attaches to the aft edge of each elevator. Functional Description When the flaps are up, the elevator tab operates in the balance mode. As the elevator moves, the tab moves in the opposite direction to elevator movement. In the balance mode, the tab moves 0.75 degrees for each degree of elevator movement. When the flaps are not up and hydraulic power is on, the elevator tab operates in the anti-balance mode. The actuator extends, moves the crank and repositions the elevator balance tab rods. When the elevator moves, the elevator tab moves in the same direction that the elevator moves. In the anti-balance mode, the tab moves 0.50 degrees for each degree of elevator movement. When the TE flaps are not up, and the FCCs send signals to the left solenoid control valve. This connects system A pressure to the actuator for the left tab. When the TE flaps are not up, there is a 10-second delay before the right actuator moves. The purpose of the 10-second delay is to improve autopilot performance. When power goes to operate the control valve it connects system B pressure to the right actuator. NOTE: With Both hydraulic system A and B failed in Manual reversion mode there is no pressure and the tabs remain in the balance mode to assist the pilot.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by StressMerchant » Fri Mar 15, 2019 12:17 pm

First let me say that I have no particular knowledge of the Max systems - I called some of my contacts at Boeing on the Max, and the response was "hmmm... we can't talk about it now, chat in a week or so". Understandable, I guess.

OK, so looking at the Max:
The Max was certified against the standards existing in about 2013. The 600/700/800 was certified against standards from about 1992. Between those two dates, one of the key changes to the regulations was the inclusion of FAR 25.143(g):
" The maneuvering capabilities in a constant speed coordinated turn at forward center of gravity, as specified in the following table, must be free of stall warning or other characteristics that might interfere with normal maneuvering: "
(The table then includes some specific test points).

Now my conspiracy theory is that 25.143(g) is behind the MCAS requirement.

25.143(g) calls for a 40 degree banked turn from level flight. As we all know, when you do a coordinated turn in level flight, stall speed increases with bank angle. At 40 degrees the stall speed increases by about 14%, and the load factor from 1G to 1.3G. If you consider normal handling being assessed from 1.3 Vsr1, the new requirement means that the gap between "normal handling" and "stall behaviour" has shrunk by about half. The regs and guidance aren't clear on the exact meaning of "characteristics that might interfere with normal maneuvering", but the basic idea (no change in slope direction) would probably apply.

So you need a compensation that increases the control force in a slow speed turn. The airspeed indicator itself is not a valid measure, since the load factor is greater than 1.0. The best measure is a combination of airspeed and AoA. And since it is essentially an augmentation system, it can probably be passed as a Level C or D software. At that level redundancy may not be required, provided that pilot action in the event of failure can fill in the gap. "Continued safe flight and landing" would be the criteria!

If you're going to augment the behavior in a turn at a constant speed, you need an AoA input. And if you're dealing with Level D software, you could probably get by with just one input. In operational terms, all you need to do is put in a little downward trim as the AoA increases, to increase the stick force gradient.

The catch is that when the system malfunctions, you'd need to identify the problem quickly and act to counter it. And perhaps that is the problem - the difference between what the certification authorities thought was a realistic "recognise and act" scenario, and what is actually happening?

My big question is, assuming that my conspiracy theory is correct, was the 600/700/800 capable of meeting the latest requirements? If not, was a requirement introduced by the FAA "for safety" actually the root cause of the MCAS system and the accidents? And were any accidents ever attributed to the lack of such a regulation?

I know. all conspiracy theories.....
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by GRAHAMW » Fri Mar 15, 2019 12:28 pm

Interesting article about satellite data contributing to the grounding of Boeing's 737 Max

The Federal Aviation Administration, or FAA, grounded Boeing's 737 Max airplanes on Wednesday, after receiving data from air traffic surveillance company Aireon about the deadly crash of Ethiopian Airlines Flight 302.

Aireon's system piggybacks on Iridium's network of 75 satellites. Expected to become fully operational in a few weeks, Aireon can track airplanes anywhere on the planet. But the company's data is already proving to be critical, as Aireon said in a statement to CNBC that "the system was able to capture information associated with Flight 302."

https://www.cnbc.com/2019/03/14/iridium ... ation.html
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jimdavis » Fri Mar 15, 2019 12:41 pm

GRAHAMW wrote:
Fri Mar 15, 2019 12:28 pm
Interesting article about satellite data contributing to the grounding of Boeing's 737 Max

The Federal Aviation Administration, or FAA, grounded Boeing's 737 Max airplanes on Wednesday, after receiving data from air traffic surveillance company Aireon about the deadly crash of Ethiopian Airlines Flight 302.

Aireon's system piggybacks on Iridium's network of 75 satellites. Expected to become fully operational in a few weeks, Aireon can track airplanes anywhere on the planet. But the company's data is already proving to be critical, as Aireon said in a statement to CNBC that "the system was able to capture information associated with Flight 302."

https://www.cnbc.com/2019/03/14/iridium ... ation.html
Very interesting - thanks Graham. :lol:

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Spoke Eagle » Fri Mar 15, 2019 1:16 pm

Hi Slow Approach, is this irridium system not the thing your're involved with?
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by CandyMan_ZA » Fri Mar 15, 2019 1:42 pm

https://www.foxnews.com/world/ethiopian ... t-says.amp

"Investigators on Friday reportedly found a piece of a stabilizer among the wreckage of the fatal Ethiopian Airline crash with its trim set in an unusual position akin to that of a Lion Air plane that crashed last year.

Two sources familiar with the matter told Reuters that investigators found the stabilizer, which moves the jet’s horizontal tail. The find could help determine whether it was set nose down for a steep dive."
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Darren » Fri Mar 15, 2019 3:28 pm

Aireon is just satellite-based ADS-B, so I would imagine ATC Kenya has the same data.

We'd have it too, if FR24 and others had better volunteer ADS-B receiver coverage in East Africa.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by cage » Fri Mar 15, 2019 3:48 pm

minor tangent, Boeing's woes continue
(CNN)In a blistering attack on Boeing, the Air Force's top acquisition official said the company has a "severe situation" with flawed inspections of its new KC-46 air refueling tanker aircraft, after trash and industrial tools were found in some planes after they were delivered to the Air Force.

Dr. Will Roper, assistant secretary of the Air Force for acquisition, technology and logistics, made clear his concerns after visiting Boeing's Everett Washington plant where the plane is assembled.
"I left concerned, and I also left thinking Boeing understands they have a severe situation that's going to take top level engagement from their company," Roper said.
After discovering the problem, the Air Force stopped accepting the new tankers from Boeing on February 20.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Christo » Fri Mar 15, 2019 7:02 pm

https://www.bloomberg.com/news/articles ... et-to-dive
screw-like device found in the wreckage of the Boeing Co. 737 Max 8 that crashed Sunday in Ethiopia has provided investigators with an early clue into what happened, as work begins in France to decode the black boxes recovered from the scene.

The so-called jackscrew, used to set the trim that raises and lowers the plane’s nose, indicates the jet was configured to dive, based on a preliminary review, according to a person familiar with the investigation.
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