Go Back  PPRuNe Forums > Flight Deck Forums > Rumours & News
Reload this Page >

Ethiopian airliner down in Africa

Rumours & News Reporting Points that may affect our jobs or lives as professional pilots. Also, items that may be of interest to professional pilots.

Ethiopian airliner down in Africa

Old 9th Apr 2019, 21:21
  #3761 (permalink)  
 
Join Date: Apr 2014
Location: NY
Posts: 6
And yet...it's the MD95, also known as the Boeing 717, that never has had a fatality..... McDonnellDouglas made a great plane...
diclemeg is offline  
Old 9th Apr 2019, 21:30
  #3762 (permalink)  
 
Join Date: Apr 2014
Location: NY
Posts: 6
Originally Posted by GordonR_Cape View Post
Avionista



I sincerely hope that Boeing engineers are doing this as we speak, otherwise they won't have a leg to stand on if this ever comes to trial. Saying that it was designed and calculated to do X and Y back in 1968, is not going to impress a jury...
Unless a jury is composed of very competent pilots, then I doubt a layman will lead to a real prosecution.
diclemeg is offline  
Old 9th Apr 2019, 21:47
  #3763 (permalink)  
 
Join Date: Jul 2009
Location: La Canada, California
Posts: 2
Only 156 produced though . . .
Dad was ATC is offline  
Old 9th Apr 2019, 21:59
  #3764 (permalink)  
 
Join Date: Aug 2008
Location: Trinidad
Age: 60
Posts: 31
“Just because the prelim report has no mention of activity during this time does not mean it was absent, we do not have a CVR transcript just a few excerpts.”

True. There is no mention of the gear up call.
dingy737 is offline  
Old 9th Apr 2019, 22:16
  #3765 (permalink)  
 
Join Date: May 2010
Location: Boston
Age: 69
Posts: 443
Originally Posted by ecto1 View Post
That's called irreversibility. A screw Jack is irreversible. A ball recirculation screw Jack is reversible. The steering of a truck as an example of the latter.

And to the poster who suggested to stick to what happened and not to what may have happened, I think he is right and I would try to post only probable theories, not merely possible ones. The trim drift is bugging me inmensely but it is probably irrelevant and the rocking explanation also fits.
Not sure context of your comment, whether just to illustrate the difference or suggest 737 uses recirculating ball screw.

To be clear the 737 does not use a ball recirculation screw Jack, it uses a acme nut and threaded rod hence irreversible .
I am not an aircraft mechanic (engineer across the pond) so I could be wrong but a quick search seems to confirm my understanding.
MurphyWasRight is offline  
Old 9th Apr 2019, 22:28
  #3766 (permalink)  
 
Join Date: Jan 2004
Location: Here and there
Posts: 2,852
Originally Posted by Chronus
With it now comes an additional instrument, the AoA indicator wired into the whole system of automation. This piece of instrumentation did have its rightful place in the cockpit of a fighter jet, with its all moving horizontal stab, but does it really also have a place in a civil transport aircraft. Especially as a command function. After all to what is known so far about this particular event is that it was the stubborn stab that took the aircraft down despite all the crews efforts to encourage it away from its determined course.
The AoA vane (not an indicator) is not new with MCAS. All airliners use AoA vanes.
AerocatS2A is offline  
Old 9th Apr 2019, 22:42
  #3767 (permalink)  
 
Join Date: Nov 2018
Location: Jakarta
Posts: 19
Originally Posted by Brosa View Post
That's what they tried to do, but it didn't engage.

It was engaged in 05:39:20 with AP CMD A for 30 seconds [off about 05:39:50], or i was wrong?

Since it engaged, the pilot confidence to told the FO retracting the flaps. 05:39:45




FDR ET AVJ
Realbabilu is offline  
Old 9th Apr 2019, 22:56
  #3768 (permalink)  
 
Join Date: May 2016
Location: Nantes
Posts: 63
Originally Posted by yanrair View Post

As you accelerate the plane pitches up due to lift being in front of cg and you need to trim nose down to fly level. And vice Versa. Lesson 1 of type rating course on sim covers this.
I know that, thank you

At low speed and with a limited amount of AND untrim, increasing speed may reduce or cancel aft column required, due to static stability of the aircraft. But in the case of ET302, even at 500 kt IAS and still both pilots pulling as much as they can, the aircraft has a -10° AoA and -2g ! No hope to reach any in-trim airspeed..

What I mean is that manual trimming was impossible due to loads on elevator (which vary as the square of airspeed) ; that the only thing that could have save the day is to slow down at a speed where loads would have permitted manual trimming.

Instead, they let full power up to VMO and above... I could not imagine why, now I know that it was what was recommended by Boeing...

Last edited by deltafox44; 9th Apr 2019 at 23:20.
deltafox44 is offline  
Old 9th Apr 2019, 23:07
  #3769 (permalink)  
 
Join Date: May 2016
Location: Nantes
Posts: 63
Originally Posted by derjodel View Post
AP disengage when AoA disagree.
No. AP has been ON for 33 seconds with AOA disagree since the rotation. It disconnected only when the captain decided to maintain runway heading while the heading selector induced a right turn.

I have read that, depending of software version, AP would disconnect after 5 minutes of stick shaker, but I don't know it is the case for ET301
deltafox44 is offline  
Old 9th Apr 2019, 23:25
  #3770 (permalink)  
 
Join Date: Jan 2010
Location: Edinburgh
Age: 82
Posts: 48
Acme nuts and threaded rods CAN be reversible, especially in a vibrating environment, as has been realised too late too many times.
But probably irrelevant in this case.
DType is offline  
Old 9th Apr 2019, 23:36
  #3771 (permalink)  
 
Join Date: Nov 2010
Location: USA
Posts: 98
Aviation Week: Boeing Expands MCAS Demos To Speed Lifting Of 737 MAX Grounding

Aviation Week: Boeing Expands MCAS Demos To Speed Lifting Of 737 MAX Grounding

Aviation Week: Boeing Expands MCAS Demos To Speed Lifting Of 737 MAX Grounding

Guy Norris Apr 9, 2019

Pilot feedback to the proposed software changes to the Boeing 737 MAX Maneuvering Characteristics Augmentation System (MCAS) flight-control law is positive, says Boeing. After demonstrations, pilots believe the potential for further flight-control problems from the system are a “nonissue,” the airframer says.

However, despite the positive response from pilots to the upgraded control system and associated training package, Boeing is gearing up for a prolonged international effort to reinstate the grounded MAX fleet. The embattled company, which first unveiled the proposed MCAS changes to a group of certification authorities and airline pilots in Seattle on March 27, is embarking on a global campaign to convince regulators that the updates will be sufficient to enable the aircraft to return to service.

The campaign encompasses a series of simulator demonstrations and briefings at multiple training sites throughout Europe, Asia and Australia and comes as Boeing attempts to handle a situation unprecedented in its history. Because the MAX was grounded first by China and other authorities around the world days before the FAA followed suit, the company says it is imperative to build support for an international caucus of regulators willing to reauthorize the MAX to return to flight.

The FAA, which in past years would have taken a lead role in such an effort, is similarly shifting gears and is now working alongside a broader group of international regulators to adjudicate the case. The agency says it expects to receive Boeing’s final package of its software enhancement over the coming weeks. Meanwhile the FAA has set up a Joint Authorities Technical Review (JATR) to conduct a comprehensive review of the certification of the aircraft’s automated flight-control system. Chaired by former NTSB Chairman Christopher Hart, the JATR is comprised of a team from the FAA, NASA and international aviation authorities.

Boeing, which on April 5 signaled a 19% production slowdown of its 737 line to ease the growing logjam of undelivered aircraft, is also providing more details about the changes to the MCAS functionality contained in the new P12.1 flight-control computer (FCC) software load that will replace the existing P11.1 software. Based on pilot reaction to date, the company says it is confident its software upgrade is certifiable.

The briefings continue to emphasize that the MCAS, which was added to the speed-trim system to standardize handling qualities with those of the 737 Next Generation, is “not a stall-protection function and not a stall-prevention function,” says Mike Sinnett, Boeing Commercial Airplanes vice president of product development and future airplane development. “It is a handling-qualities function. There’s a misconception it is something other than that.“

Added to ensure a linear relationship between stick force per G, “speed trim is a function of airspeed, so if you’re going fast, it’s a low angle-of-attack (AOA), and if you’re going slow, it’s at higher AOA,” he notes. “The thing you are trying to avoid is a situation where you are pulling back and all of a sudden it gets easier, and you wind up overshooting and making the nose higher than you want it to be.”

Underscoring the difference between the speed-trim system on the 737 Next Generation (NG) and the MAX, Sinnett says: “Mechanically, on the NG there is a column cutoff switch that stops any automatic trim when the column is back to a certain spot. On the MAX, we still needed automatic trim when you got to that spot. MCAS differs from speed trim at elevated alpha because it bypasses that switch by design. To do that, it activates based on AOA rather than based on speed—which is what speed trim does. Speed trim is a function of airspeed, and MCAS is a function of angle-of-attack and Mach number, but it only triggers off AOA.”

In the initial briefing sessions for pilots on March 27, “we didn’t talk specifically about either of the accidents, but we ran through MCAS scenarios,” says Sinnett. “From the accidents, we now know how MCAS can behave when there is an erroneously high AOA input, so we walked through scenarios where that could occur. We demonstrated those in the simulator.”

In these sessions, pilots and regulators were able to interact via intercom and a big screen with Boeing pilots in the 737 MAX engineering cab. Following the sessions, “we went back to the classroom and said, ‘Here are the things that concern us most when we look at the scenario of the two accidents we just experienced,’” Sinnett says. “Upon reflection on what has occurred, it appeared the system could present a high-workload environment—and that’s not our intention. So we looked at changing the design to compare values from multiple AOA indicators to essentially eliminate the unintended trigger condition that causes MCAS to activate."

Sinnett says pilots appear satisfied that the three main layers of protection now added to the MCAS will prevent any potential repeat of the circumstances involved in the Lion Air and Ethiopian Airlines accidents. “We answered a lot of questions during the discussion, and then we went back into the simulator and demonstrated a number of different scenarios to run against these changes,” Sinnett says. “And the most compelling thing is that the AOA failure case turns into a run-of-the-mill AOA failure case like you might have on any other airplane. We didn’t get any negative feedback. It was all very positive, and any of the pilots who got into the simulator and saw the before and after, it was like, ‘Yes, OK, this is now a nonissue.’”

The first main layer of protection provided by the update is a cross-channel bus between the aircraft’s two FCCs, which now allows data from the two AOA sensors, or alpha vanes, to be shared and compared. AOA data continues to be fed from left and right vanes into their respective air data inertial reference units before being passed to the flight computers. However, the AOA data in both computers is now continuously compared. The change is made by software only and requires no hardware modification.

“In a situation where there is erroneous AOA information, it will not lead to activation of MCAS,” says Sinnett. He underlines that the entire speed-trim system, including the MCAS, will be inhibited for the remainder of the flight if data from the two vanes varies by more than 5.5 deg. If an AOA disagreement of more than 10 deg. occurs between the sensors for more than 10 sec., it will be flagged to the crew on the primary flight display.

The second layer of protection is a change to the logic in the MCAS algorithm that provides “a fundamental robust check to ensure that before it ever activates a second time, pilots really want it to activate,” says Sinnett.

The change would have protected the system from continuing to activate in the case of the Lion Air accident, in which the left AOA vane was stuck in the 20-deg.-nose-high position. In that circumstance, the logic rechecked if the MCAS was required and, registering the apparent nose-high position from the errant vane, commanded more nose-down trim. “Now it sees you’re in the same spot, it says you’ve got a stuck vane and says, ‘I’m not going to activate again,’” Sinnett notes.

“That’s assuming it will activate in the first place, which it won’t because one AOA vane with a high value won’t activate,” he adds. “When you do defense in depth, you have to artificially fail one layer to make sure you adequately design and test the next layer—so that’s what we had to do.”

Explaining the background to the third layer of protection, Sinnett says: “We also made sure if the second layer of protection failed somehow in some weird way and allowed MCAS to activate multiple times, the system now ensures the sum total is command-limited.” The result is that the pilots always have maneuvering authority remaining with the control column. “Pilots will always have the ability to override—although they had that before in other ways, like with the trim switch, for example. But with the software update, the column itself will always provide at least 1.2g of maneuvering capability. So you don’t just have the ability to hold the nose level, you can still pitch up and climb.”
airman1900 is offline  
Old 9th Apr 2019, 23:40
  #3772 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 12,496
Originally Posted by MurphyWasRight View Post
To be clear the 737 does not use a ball recirculation screw Jack, it uses a acme nut and threaded rod hence irreversible .
I am not an aircraft mechanic (engineer across the pond) so I could be wrong but a quick search seems to confirm my understanding.
No, that's not correct.

DaveReidUK is offline  
Old 9th Apr 2019, 23:41
  #3773 (permalink)  
 
Join Date: Jun 2009
Location: Europe
Age: 51
Posts: 11
Originally Posted by Realbabilu View Post
It was engaged in 05:39:20 with AP CMD A for 30 seconds [off about 05:39:50], or i was wrong?

Since it engaged, the pilot confidence to told the FO retracting the flaps. 05:39:45



FDR ET AVJ
Take a look at the blue line named "AP Warn CAPT".
That's the autopilot disconnect warnings they got.
You get that warning when
1. autopilot has disengaged.
2. an autopilot engage attempt is made and is unsuccessful.

The first two warnings were because of the unsuccessful attempts to engage the autopilot at around 400 ft.
The third warning was when it was disconnected after about 30 sek on autopilot.

But there is also a fourth warning at 05:43:15, right after they made those two quick trim inputs.
It certainly looks like they made a failed attempt to engage the autopilot here, doesn't it?


Was that the plan?
To turn the trim cutout switches back on so they could reengage the autopilot, hoping the automation would sort out their problems?
Brosa is offline  
Old 9th Apr 2019, 23:42
  #3774 (permalink)  
 
Join Date: May 2010
Location: Boston
Age: 69
Posts: 443
Originally Posted by DType View Post
Acme nuts and threaded rods CAN be reversible, especially in a vibrating environment, as has been realised too late too many times.
But probably irrelevant in this case.
True, but they can be designed to reliably lock if the conditions are known.
There is a discussion of this in the Lion Air thread, I remember that the consensus seemed to be that it is unlikely to happen in the 737 design, certainly not enough to cause a noticeable issue.
I recall that one point is that Boeing would have designed it to not drift with vibration to eliminate need for an independent brake.
MurphyWasRight is offline  
Old 10th Apr 2019, 00:11
  #3775 (permalink)  
 
Join Date: Oct 2017
Location: Tent
Posts: 707
So the Boeing software fix.

When you get a AOA disagree MCAS will not engage, and the "safety" requirement stick force feedback will not be there.

Is the feel of the stick there to assist the pilot not to over pitch? and is the feel of the feedback not best to have when you have falling items such as the AOA's.

I think this is not a satisfactory fix, as simply not having MCAS would be safer.
Bend alot is offline  
Old 10th Apr 2019, 00:37
  #3776 (permalink)  
 
Join Date: Aug 2007
Location: Alabama
Age: 55
Posts: 366
A stupid question from a SLF, how many not FBW aircrafts needed a software patch to certified? I cannot understand why a main control surface has to be actuated by HAL on a not FBW aircraft, when the certification requirements could be fulfilled with a redesigned feel system, I understand that such will imply no grandfathering, but still, if the problem is pilot feel, adjust the feel, without moving control surfaces...
I apologize if the above sounds stupid, but would like to have a proper understanding ...
thanks for your patience
FrequentSLF is offline  
Old 10th Apr 2019, 00:37
  #3777 (permalink)  
 
Join Date: May 2010
Location: Boston
Age: 69
Posts: 443
Originally Posted by DaveReidUK View Post
No, that's not correct.

Thanks.
I stand corrected,looks like it is indeed a ball screw.

I was misled by more than one diagram referring to the above assembly as a 'nut', some even said 'acme nut'.
That and reading the Alaska Air report which did have a nut rather than ball screw.

This is a good illustration of the pitfalls of using other than detailed drawings/schematics for analysis.
So far in this thread I have seen only one what looks to be a true schematic, the yoke trim switches with wire# but unclear labels, everything else has been a conceptual logic illustration or worse.

Same thing applies to reading the fdr plots without access to the numerical data and other factors such as sampling rates.
I suspect that the sloped lines on binary events on the plots might represent sampling uncertainty but have no way of knowing.
MurphyWasRight is offline  
Old 10th Apr 2019, 00:38
  #3778 (permalink)  
Psychophysiological entity
 
Join Date: Jun 2001
Location: Tweet Rob_Benham Famous author. Well, slightly famous.
Age: 81
Posts: 4,910
airman1900 #3824

Taken from Mike Sinnett's publication:

Underscoring the difference between the speed-trim system on the 737 Next Generation (NG) and the MAX, Sinnett says: “Mechanically, on the NG there is a column cutoff switch that stops any automatic trim when the column is back to a certain spot. On the MAX, we still needed automatic trim when you got to that spot.
The bee in my bonnet about that rear column cut-off switch having been removed on the MAX, is it seems, still open to interpretation. The inference is there, but not the positive statement.
Loose rivets is offline  
Old 10th Apr 2019, 00:55
  #3779 (permalink)  
 
Join Date: Sep 2001
Location: Toronto
Posts: 2,266
From the horse's mouth

Underscoring the difference between the speed-trim system on the 737 Next Generation (NG) and the MAX, Sinnett says: “Mechanically, on the NG there is a column cutoff switch that stops any automatic trim when the column is back to a certain spot. On the MAX, we still needed automatic trim when you got to that spot. MCAS differs from speed trim at elevated alpha because it bypasses that switch by design. To do that, it activates based on AOA rather than based on speed—which is what speed trim does. Speed trim is a function of airspeed, and MCAS is a function of angle-of-attack and Mach number, but it only triggers off AOA.”
The software is getting modified - should be good as long as both vanes don't get taken out by a flock and the algorithm to always leave 1.2 g authority in the elevator attains 10E-9 reliability.

What I haven't seen yet is a procedure to block MCAS in certain stick shaker cases, especially on rotation or early takeoff.
RatherBeFlying is offline  
Old 10th Apr 2019, 01:04
  #3780 (permalink)  
 
Join Date: Dec 2014
Location: Schiphol
Posts: 346
9th Apr 2019, 23:38 #3831 (permalink) Loose rivets

airman1900 #3824 Taken from Mike Sinnett's publication:

Underscoring the difference between the speed-trim system on the 737 Next Generation (NG) and the MAX, Sinnett says: “Mechanically, on the NG there is a column cutoff switch that stops any automatic trim when the column is back to a certain spot. On the MAX, we still needed automatic trim when you got to that spot."
@LooseRivets - The bee in my bonnet about that rear column cut-off switch having been removed on the MAX, is it seems, still open to interpretation. The inference is there, but not the statement.
The article also states:

On the MAX, we still needed automatic trim when you got to that spot. MCAS differs from speed trim at elevated alpha because it bypasses that switch by design.
Bypassing could also mean the switch is still there for use by other systems. So no removal?

Next to that you would like to know things like if we are talking column or columns. How many switches are there. Are they NG or MAX only. Etcetera, etc… Is there an official Boeing press release with this information? … stilll many questions…

So, Mr Sinnett’s statements add something but are not clear enough and not deep enough. Many would welcome more.

I posted earlier in the thread that my impression was that only a detailed public presentation and publication by the ‘chief engineer (with FAA delegated certification signature authority)’ of the MAX would do. I wonder if Mr Sinnett fits that bill? The text has a ‘nice and sunny taste’, rather more commercial than tech savvy …
A0283 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.