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 13th Mar 2019, 04:44
  #921 (permalink)  
 
Join Date: Dec 2000
Location: 30W
Posts: 64
bunk exceeder is offline  
Old 13th Mar 2019, 04:49
  #922 (permalink)  
 
Join Date: Mar 2010
Location: L.A.
Age: 52
Posts: 561
Originally Posted by FCeng84 View Post
. With this in mind, the nose up thrust induced pitching moment generated by the 737MAX engine is not greater than that for a 737NG. In fact, it is probably less as the center line of the larger MAX engine is higher than the center line of the smaller NG engine given their respective attachment geometries.

Hopefully it is now clear that the pitching moment of concern with the 737MAX engines that gives rise to the need for MCAS is related to the aerodynamic impact of the engine cowling location and geometry, not the magnitude nor location of the thrust vector generated by those engines.
Yes, but the 737NG already had a thrust induced pitch problem, as was amply demonstrated by the Bournnemouth incident, where an NG pitched up to 47 degrees - mostly caused by increased thrust when close to the stall. I have no doubt that Boeing had this problem in mind when they chose to implement the MCAS system. (This was sufficiently well known to already be in the simulator software, which would happily pitch you to 90 degrees up if you got too slow with full power applied.)

The problem being that the MCAS solution was ill thought out and badly designed. The system needed multiple inpututs, including airspeed and attitude. It needed greater redundancy, with another AoA sensor. It needed more refined logic, instead of running to full forward trim, which no aircraft should ever do. It needed greater error checking, to disable the system if faults or data discrepancies were detected. And it really needed to act on the elevator and thrust levers, rather than the stab (ie: reducing the thrust when close to the stall, as per the QRH recommendation).

Apart from that, it was a great design....

Silver
silverstrata is offline  
Old 13th Mar 2019, 04:54
  #923 (permalink)  
 
Join Date: Aug 2005
Location: Bangkok
Posts: 28
Originally Posted by FCeng84 View Post
While there is not yet sufficient information to draw a clear link between the ET accident that is the subject of this thread and MCAS I am deeply troubled by the amount of misinformation regarding MCAS that is being spread here. Reluctantly I offer the explanation below without any suggestion that this system contributed to the tragedy in Ethiopia this last weekend. The truth will be revealed by the recorder data and the full investigation. I strongly implore those who do not know MCAS details to stop providing incorrect information here or anywhere else. Posing questions is fine, but please do not state as fact that about which you are not sufficiently knowledgeable.

MCAS Operation Clarification

MCAS is triggered when all of the following are true:
A. Sensed AOA exceeds a flight condition based activation threshold
B. Flaps are fully retracted (i.e., up)
C. Autopilot is not engaged

When triggered, MCAS commands nose down stabilizer as a function of how much AOA has exceeded the activation threshold and the current Mach number. For large exceedence of the MCAS activation AOA threshold, MCAS will command 2.5 degrees of stabilizer at low Mach number but less than 1/3rd of that at cruise Mach number (gradual Mach number based schedule between). For a lesser exceedence of the MCAS activation AOA threshold the size of the stabilizer increment will be proportionally less. MCAS stabilizer command will be stopped immediately upon pilot activation of pitch trim. (Pilot trim input also serves as MCAS reset - see next paragraph.)

Once MCAS has commanded one increment of stabilizer motion, it will not command more until it has been reset. MCAS is reset if any of the following occur:
1. Pilot makes a manual trim command. (MCAS will not re-activate until there have been 5 continuous seconds without pilot trim command.)
2. AOA drops below MCAS activation threshold and MCAS has run stabilizer in the airplane nose up direction taking out the increment of airplane nose down command it inserted earlier.
3. Autopilot is engaged and then disengaged.

Without pilot trim input, MCAS will not run the stab more than one increment (up to 2.5 degrees) unless MCAS is reset via either 2 or 3 above.

Talk of MCAS running the stabilizer for 10 seconds, pausing for 5 seconds, and then running it again repeatedly without pilot trim input are patently incorrect.
So, to cut a long story short if the AOA and/or air speed readings are incorrect its actions are worse than doing nothing.
Innaflap is offline  
Old 13th Mar 2019, 04:55
  #924 (permalink)  
 
Join Date: Sep 2008
Location: Australia
Posts: 40
Originally Posted by rh2600 View Post
If ever you wanted a good example of regulatory capture, the continuum with China sitting at one side champing at the bit to throw at stone at a US company at the first hint of smoke, and the FAA sitting right at the other holding fast while everyone else sees a fire is a pretty great illustration of the effect.
The FAA needs to set their weather radar to "Shit Storm". Because that's what is ahead.
Aloha_KSA is offline  
Old 13th Mar 2019, 05:03
  #925 (permalink)  
 
Join Date: Mar 2019
Location: Australia
Posts: 2
Boeing 777 Certification

re the comments on this thread about FAA’s willingness to allow certification of a software fix to overcome other issues I recall the 777 was certified to fly over water with only 2 engines after computer simulations only. This was despite certifications up to that time requiring real world testing before certification. 737 Max experience might be part of the continuing trend to engineer workarounds.
KJSlice is offline  
Old 13th Mar 2019, 05:03
  #926 (permalink)  
 
Join Date: Jan 2008
Location: australia
Posts: 114
In long ago days of “excessive government red-tape” new airliners were assessed and certificated by aviation authorities in each country where they flew. For Boeing aircraft we all now rely on certification by the US Federal Aviation Administration and in turn FAA delegates most analysis and testing to Boeing.

Until recently senior company engineers called ''Designated Engineering Representatives'' assessed compliance on behalf of FAA. Delegation went further on the Boeing 787. It was first airliner approved under a new ''Organisation Designation Authorisation'' (ODA) arrangement, specifically intended to reduce FAA involvement.

Somehow hazardous lithium ion batteries slipped undetected through the new procedures. Several batteries caught fire and the 787 was grounded. Independent National Transportation Safety Board investigators found:
  • “Boeing’s electrical power system safety assessment did not consider the most severe effects of a cell internal short circuit and include requirements to mitigate related risks, and the review of the assessment by Boeing authorized representatives and Federal Aviation Administration certification engineers did not reveal this deficiency."
  • ”Boeing failed to incorporate design requirements in the 787 main and auxiliary power unit battery specification control drawing to mitigate the most severe effects of a cell internal short circuit, and the Federal Aviation Administration failed to uncover this design vulnerability as part of its review and approval of Boeing’s electrical power system certification plan and proposed methods of compliance."
  • "Unclear traceability among the individual special conditions, safety assessment assumptions and rationale, requirements, and proposed methods of compliance for the 787 main and auxiliary power unit battery likely contributed to the Federal Aviation Administration’s failure to identify the need for a thermal runaway certification test.”

737 Max is second aircraft to be certificated under ODA. After two fatal accidents FAA and Boeing claim the aircraft is safe but admit that mandatory design changes are needed to a Maneuvering Characteristics Augmentation System (MCAS) which is unique to the MAX.

In a “Continued Airworthiness Notice to the International Community” FAA says its “oversight activities” include:
  • Boeing’s completion of the flight control system enhancements, which provide reduced reliance on procedures associated with required pilot memory items. The FAA anticipates mandating these design changes by AD no later than April 2019.
  • Design changes include:
  1. · MCAS Activation Enhancements
  2. · MCAS AOA Signal Enhancements
  3. · MCAS Maximum Command Limit

Which confirms Boeing is running the show and almost invites foreign authorities to play safe and ground the Max.

Who’s ever heard of a “CANIC”? Surely a Notice of Proposed Rule Making is required?

Boeing and FAA swept Lionair accident under the carpet but cannot do same with Ethiopian because it’s more reputable and real people (US and UN) were killed; not just Indonesians on an LCC.
ozaub is offline  
Old 13th Mar 2019, 05:07
  #927 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 47
Originally Posted by silverstrata View Post


The broken part was a MCAS system that reacted to a single faulty input - instead of comparing that input with its partner; deciding there was a discrepancy; and switching itself off.

On second thoughts, the real broken parts were the designers and engineers who thought that MCAS was a good idea. It looks to me like a case of group confirmation bias, were a small cabal decide upon an action, and they have sufficient authority that nobody else will question their wisdom. As someone said above, flight crews have to do CRM every year, so do Boeing engineers do DRM or ERM every year? (design or engineering resource management)

Silver

Originally Posted by acad_l View Post
True. But the Airbus planes are stable throughout their flying envelope. The Max alas is not. The FAA should have never allowed a software fix as a remedy for a basic design flaw. And there must have been engineers at Boeing who were very upset of having been overruled by bean counters and MBA types. Admittedly the MCAS as it is today is a remedy (to the symptoms) worse than the disease. But there should never have been an MCAS in the first place, the right thing to do was to redesign the horizontal stabilizer.

Only airliner I can think of that turned out to have a stability issue was the BAC-111. But that was found late in the game, not by design, and the remedy apparently worked.

Don't get me wrong, I totally agree. The 737 should stop at 150 people and 3 hours, (if B wants a bigger plane start building the 757NG.) If you have stretched your plane so far you need an extra telescoping landing gear and higher speeds to prevent a tailstrike, and software trimming because of inherent instability you are doing something wrong. If you implement said band-aid with a single source input and call it a day, you are well on your way to criminal negligence. MCAS should never have been designed, build or approved this way, my post was just a reply to someone who was more scared of software than hardware, and I disagreed with his POV.
hans brinker is offline  
Old 13th Mar 2019, 05:09
  #928 (permalink)  
 
Join Date: Nov 2018
Location: Jakarta
Posts: 19
Originally Posted by ReturningVector View Post



And how many times did the pilots save the airplane from the automation?
at least those pilots who saved the previous pk-lqp Dps-cgk lion air won against Mcas accident, without knowing Mcas even existed and stick shaker blaring all along flight.
as a pax, are these pilots that could handle this situation are rare or not ?
if not then Boeing should really re examined their mcas, and aoa parts should be on MEL.
But could whole AOA system tested on ground ?

Last edited by Realbabilu; 13th Mar 2019 at 06:41.
Realbabilu is offline  
Old 13th Mar 2019, 05:10
  #929 (permalink)  
 
Join Date: Aug 2007
Location: Alabama
Age: 54
Posts: 366
US FAA will issue a statement, only once or US airlines will have adjusted their workload, be able to replace the MAX without losing money. Sector by sector
FrequentSLF is offline  
Old 13th Mar 2019, 05:13
  #930 (permalink)  
 
Join Date: Jan 2000
Posts: 210
Originally Posted by crosscust View Post
MCAS is operational with flaps up. Most (if not all) airlines do not start retracting flaps till 3000’ AFE. According to reports, Ethiopian never achieved anything higher than about a 1,000’ (not even close to 3k).


Clearly you have never left the US and are not familiar with the various forms of noise abatement procedures used worldwide. Google NADP2 (Proc B) and you'll understand most non-US carriers worldwide routinely accelerate and commence flap retraction at >800' (NADP2) or >1000' (Proc B) above 1000' AFE.

Noise Abatement Procedures

Last edited by Dune; 13th Mar 2019 at 05:35.
Dune is offline  
Old 13th Mar 2019, 05:23
  #931 (permalink)  
gmx
 
Join Date: Nov 2018
Location: Brisbane
Posts: 25
Originally Posted by hans brinker View Post
Don't get me wrong, I totally agree. The 737 should stop at 150 people and 3 hours, (if B wants a bigger plane start building the 757NG.) If you have stretched your plane so far you need an extra telescoping landing gear and higher speeds to prevent a tailstrike, and software trimming because of inherent instability you are doing something wrong. If you implement said band-aid with a single source input and call it a day, you are well on your way to criminal negligence. MCAS should never have been designed, build or approved this way, my post was just a reply to someone who was more scared of software than hardware, and I disagreed with his POV.
We are still awaiting confirmation that MCAS is responsible for either crash.
gmx is offline  
Old 13th Mar 2019, 05:25
  #932 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 47
Originally Posted by Luc Lion View Post
There are such switches, although they are hidden in the column.
See FCOM 9.20 "Controls - System Description" - "Stabilizer Trim".
Read also the function of the "Stabilizer Trim Override Switch"
Thanks for the correction, not on the 737 myself.
hans brinker is offline  
Old 13th Mar 2019, 05:26
  #933 (permalink)  
 
Join Date: Jun 2001
Location: Rockytop, Tennessee, USA
Posts: 5,432
Originally Posted by Dune View Post

Clearly you have never left the US and are not familiar with the various forms of ICAO noise abatement procedures. Google NADP1 vs NADP2 and you'll understand most non-US carriers worldwide routinely accelerate and commence flap retraction (NADP2) above 1000' AFE.

http://www.b737mrg.net/downloads/b737mrg_noise.pdf
Looks like this lad is trying to get some international experience at QR:

Originally Posted by crosscust View Post
FMC Overheat: Was the offer for a DEC or an FO? Thanks. Just wondering what they're interviewing for.
I wish him well in his future endeavors.

Airbubba is online now  
Old 13th Mar 2019, 05:37
  #934 (permalink)  
 
Join Date: Mar 2019
Location: Australia
Posts: 2
I’m not sure there was any suggestion this caused the latest accident- just that it’s bad design.
KJSlice is offline  
Old 13th Mar 2019, 05:39
  #935 (permalink)  
 
Join Date: Apr 2009
Location: PugetSound
Age: 72
Posts: 47
What does the data say?

Non-pilot but expert number cruncher with a basic questions about the DATA shown in post 69 and several prior to that.

Looking at the ADS-B numbers, in ascending time sequence from the start of the takeoff roll at 05:38:01Z, I see:

18 seconds with 0 elevation gain (to 7,200') and acceleration from 0 to 93 knots (ETH-302 still on the runway?)
5 seconds with 25' elevation gain (to 7,225') and acceleration from 93 to 105 knots (ETH-302 still on the runway?)
11 seconds with 00' elevation gain (to 7,225') and acceleration from 105 to 154 knots
11 seconds with 25' elevation LOSS (to 7,200') and acceleration from 154 to 183 knots (did ETH-402 try to lift off runway and then settle back on to it?)
14 seconds with 25' elevation gain (to 7,225') and acceleration from 183 to 200 knots

59-seconds after beginning the takeoff roll - the plane was at 200-knots and had gained NO altitude above the runway (based on elevation at 105-knots). Is that possible?

At 59-seconds there could not be much of the ~12,465' runway left ahead of the plane since it had been doing an average of 150-knots (250 fps) for 33-seconds (8,250') and had travelled about 3,000' accelerating in the first 26-seconds.. At what point would the takeoff be rejected? Or is this just a normal takeoff at a hot and high airport?

I assume MCAS could not have been active during the first 60-seconds of the takeoff event.

Continuing with the sequential timestamps:

50-seconds with 925' elevation gain (to 8,150') and acceleration from 200 to 263 knots.
25-seconds with 450' elevation LOSS (to 7,700') and acceleration from 263 to 323 knots.
45-seconds with 900' elevation gain (to 8,609') and acceleration from 323 to 283 knots.

From the time ET-402 reached 226-knots at 7,575' there were 33 ADS-B reports of which only 7 showed a loss of altitude and they all occurred in a 21-second period (5:39:55 to 5:40:16)

During the period 5:40:09 to 5:40:45 the plane maintained an altitude of 7,750' +25'/-50'.

From 5:40:35 to 5:41:02 (end of data) the plane climbed steadily and gained 875' while accelerating to 383-knots.

How does the data above fit with the theory of MCAS forcing a rapid descent?
TacomaSailor is offline  
Old 13th Mar 2019, 05:41
  #936 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 47
Originally Posted by 4runner View Post
The 737 incurs a pitch up moment with additional thrust because of engine placement and moment. Not because of “lift”. I’m glad you’re working on your multi engine ratings right now and went over vmc factors including accelerated induced flow.
I think you are replying to me but don't know how to use the quote function.
Sorry to disappoint you, but I have 5 type ratings, 10K+ hours, FAA ATP & JAA ATPL.
And as explained more clearly below MCAS has nothing to do with thrust, and everything with aerodynamics.
I suggest you read it, and let me know if you need any more help becoming less condescending.

Originally Posted by FCeng84 View Post
Hans - your patience is amazing. You are correct about the relationship between 737MAX engines and need for MCAS. It has nothing to do with the thrust pitching moment!!!

There is a cert requirement that as AOA increases, the nose up pilot command required must not decrease. This is demonstrated at fixed thrust levels so there is no change in thrust pitching moment. The 737MAX issue here that gives rise to the need for MCAS is that as AOA increases the lift provided by the engine cowling that is so large and mounted so far forward of the wing causes a nose up pitching moment that results is a decrease in the column pull needed to maintain a steady positive AOA rate. That characteristic is not compliant with the requirements. MCAS comes active during this maneuver putting in nose down stabilizer that must be countered by the column. The net effect of engine cowling lift and MCAS nose down stabilizer as AOA increases is that the column needed to complete the maneuver does not decrease part way through the range of AOA for which characteristics must be demonstrated. 737MAX without MCAS fails the cert demo. 737MAX with MCAS passes the cert demo.
hans brinker is offline  
Old 13th Mar 2019, 05:50
  #937 (permalink)  
 
Join Date: Nov 2010
Location: Denver
Age: 52
Posts: 47
Originally Posted by gmx View Post
We are still awaiting confirmation that MCAS is responsible for either crash.
We don't know about Ethiopian, but I am convinced Lion Air is directly caused by faulty AOA info to MCAS. Should the pilots have been able to recover like the ones did the day before? Probably/absolutely, but that doesn't change that the MCAS design is a major problem.
hans brinker is offline  
Old 13th Mar 2019, 06:10
  #938 (permalink)  
gmx
 
Join Date: Nov 2018
Location: Brisbane
Posts: 25
Originally Posted by hans brinker View Post
We don't know about Ethiopian, but I am convinced Lion Air is directly caused by faulty AOA info to MCAS. Should the pilots have been able to recover like the ones did the day before? Probably/absolutely, but that doesn't change that the MCAS design is a major problem.
You are likely correct about Lion, but it is yet to be confirmed. There were flight control issues on that aircraft prior to the ineffective (unwarranted?) replacement of the AoA vane.
gmx is offline  
Old 13th Mar 2019, 06:32
  #939 (permalink)  
 
Join Date: Dec 2017
Location: home
Posts: 42
Originally Posted by hans brinker View Post
..... If you have stretched your plane so far you need an extra telescoping landing gear and higher speeds to prevent a tailstrike, and software trimming because of inherent instability you are doing something wrong.

Well, while not exactly the same, I guess you think they better dump the 777-300ER as well due to the design features needed on that jet??
greenfields is offline  
Old 13th Mar 2019, 06:35
  #940 (permalink)  
 
Join Date: Oct 2017
Location: Vienna
Posts: 117
Originally Posted by RatherBeFlying View Post
By the time a MAX 8 or 9 has made it to cruise, the phase of flight that claimed Lion and ET is long past. And the pax have to land somewhere, preferably within reasonable reach of destination.
MCAS event could happen at any phase of flight. You just need: a failed AoA sensor, AP disengaged (would failed AoA disengage AP?) and flaps up.
derjodel 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.