Leeham News and Analysis
There's more to real news than a news release.
Leeham News and Analysis
- Solid start for stand-alone GE Aerospace despite cuts to LEAP output April 23, 2024
- SPEEA, Boeing at impasse over safety program, union says April 23, 2024
- Better transparency needed on Boeing’s 1Q earnings call April 22, 2024
- Bjorn’s Corner: New engine development. Part 4. Propulsive efficiency April 19, 2024
- Boeing unlikely to meet FAA’s 90-day deadline for new safety program April 18, 2024
Bjorn’s Corner: Analysing the 737 MAX crashes
October 25, 2019, ©. Leeham News: To better understand what went wrong in the Boeing 737 MAX crashes I have over the last half-year run Corner series around aircraft Pitch stability and Aircraft Flight Control systems and how these attack the problems of today’s airliners need for stable characteristics over a very wide flight envelope.
With this as a backgound, we will now in a series of Corners go into the Lion Air final crash report which is issued today, to understand what happened and why.
What have we learned and how can we use it
We started with articles looking into the crashes and what the preliminary reports from Lion Air JT610 and ET302 could tell us.
The reports showed how an augmentation system, the MCAS (Maneuver Characteristic Augmentation System) that should help the pilot at the extreme of the aircraft’s flight envelope had misfired and caused the aircraft to crash.
To better understand why a system like MCAS is needed for modern airliners we ran a 10 week Corner series about the Pitch stability of aircraft and the problem areas of providing consistent pitch stability over the aircraft’s wide flight envelope.
We learned the most critical axis of movement for an aircraft is the pitch axis and that the pilot needs a consistent and stable aircraft over a speed range from 100kts to within 20% of the speed of sound and over an altitude from the ground up to 41,000ft.
The natural aerodynamics of modern aircraft does not provide a consistent and stable platform over this speed and altitude range without special means to help with the stability.
Some fixes can be made aerodynamically but others need the flight control system to augment the control feeling for the pilot (MCAS is an example of such a system) or to protect him from phenomenons like Mach tuck.
To understand how different flight control systems handle these needs for improved feel and protection we ran a 13-week series on Flight Control architectures and their capabilities when providing such assistance.
With this knowledge, we now use the next Corners to analyze the Lion Air final report.
“A critical sensor providing data to an anti-stall system had been miscalibrated by a repair shop in Florida and that there were strong indications that it was not tested during installation by Lion Air maintenance staff, the report said.”
That doesn’t explain the incident of previous flight which results in AoA replacement. Inculding ET, all of them experience similar AoA malfunction.
And how they know it was mis-calibratded. Did they recover the AoA from the site?
from the report
http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/2018%20-%20035%20-%20PK-LQP%20Final%20Report.pdf
page 284
Removed Angle of Attack sensor (P/N 0861FL1; S/N 21401)
Lion Air removed AOA sensor Part Number (P/N) 0861FL1 Serial Number (S/N)
21401 from PK-LQP aircraft on 28 October 2018 to address a maintenance write-up
stating that the speed (SPD) and altitude (ALT) flags appeared on the Captain’s
PFD. Following the accident, BATAM Aero Technik provided the removed AOA
sensor to KNKT on 5 November 2018. The KNKT subsequently provided the
sensor to the United States National Transportation Safety Board (NTSB) for
further examination and detailed testing.
On 10 December 2018, representatives from the KNKT, NTSB, FAA, and Boeing,
convened at a Collins Aerospace (previously known as Rosemount Aerospace)
facility to perform examination and testing of the AOA sensor in accordance with
the Collins Aerospace Component Maintenance Manual (CMM) 34-12-34,
Revision 9. Examination of the AOA sensor revealed an intermittent open circuit in
the resolver #2 coil wiring. At temperatures above approximately 60°C, the
resolver functioned normally, but did not function below that temperature.
The test conducted according to the Rosemount Aerospace Inc., Component
Maintenance Manual (CMM) 0861DR, 0861FL, 0816DR MOD1 and 0861FL1
Chapter 34-12-34 Table 1005 Test Data Sheet.
The vane travel test was performed per the test procedure contained within CMM
34-12-34. The AOA sensor passed the requirements for the vane travel at the
clockwise (CW) and counter clockwise (CCW) end stops of the unit when the
output from Resolver 1 was utilized. The Resolver 1 output is what is used as the
requirement within the CMM.
The vane travel was also evaluated using Resolver 2 of this unit. This test would not
normally be required within the CMM. The test unit, 0861FL1, SN 21401, failed
the requirements for the vane travel at the CW and CCW end stops of the unit. The
expected outputs from Resolver 2 were not sinusoidal in nature and therefore the
recording instrument could not interpret them. Therefore, the outputs from Resolver
2 were identified on the test data sheet as “unstable.” ….goes on
Thanks.
IMO, page 248 of report describes defects in the replaced AoA before accident, not the AoA on the accident plane.
Page 89~91 explains possible way how bias ( mis-calibration) could be introduced during an AoA repair. IMO, there isn’t explicit evidence that AoA in accident plane was miscalibrated one.
After the crash KNKT gave the AoA sensor from the previous flight to the US NTSB.
Ethiopia was clever. IIRC an US agency asked for the FDR, but Ethiopia didn’t want to give it to US. They preferred Germany, but Germany couldn’t read it out, so France got it.
Some interesting details here on the AOA.
https://www.flightglobal.com/news/articles/lion-737-max-inquiry-uncertain-over-swapped-sensor-t-461809/
You can conclude that if you don’t have the data then the test was not done.
Could you be a bit more specific about what is clever about that, and what you believe a US investigative agency (or even Boeing for that matter) would have done with the EA FDR if it had been given to them? Destroy it accidently-on-purpose? Alter the data? What exactly is the basis of such accusations? Thanks.
Clearly Ethiopian airline and or the government did not trust the US.
That included the NTSB which is not complicit in any of the issues (just the contrary).
But you cannot blame them for a lack of trust as the FAA and Boeing tarred the NTSB in this case as well and politically it was not a fight one or both of the two involved (Ethiopian airline and or government) did not want to deal with.
sPh
If I’m responsible for an investigation and another country is asking me to hand out important things, I would ask myself, why do they want to have it, especially if that country could be the one responsible for the crash.
There was no reason to hand out the AoA sensor.
Maybe I would give them an AoA sensor, but another one I manipulated, just to see what they will find out.
What do we have here.
Boeing, who doesn’t respect regulations, who is hiding and cheating.
FAA, who doesn’t control regulations, who was the last to ground the MAX.
Congress, which is pushing FAA not to regulate.
Presidents, who are pushing not to regulate and not funding the FAA enough.
What are their intentions to do this?
We will see what the FAA will do now. I expect the FAA will not respect regulations and will certify some crap.
Why do I expect this, shouldn’t I have 100% trust in the FAA to implement all safety standards?
Patrick Ky’s PowerPoint presentation to the European Parliament says EASA got involved because Ethiopia wanted them as an advisor.
My question is, why was the AoA sensor failing repeatedly when brand new? By all rights the MCAS problems should’ve take YEARS to show up at all.
AOA’s aren’t that reliable, and didn’t need to be before MCAS depended on them to fly the aircraft .. look at any accident database for AOA errors
for example..
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https://avrodex.com/?q=aoa
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Yes I have repeatedly brought up the point that they have issues.
More relevant is that they used a bogus set of data (allowed but should not be) based on AOA internal failures vs all causes (including bird and ramp strikes)
Boeing could ask FAA to ensure that the full data set is used but did not.
Another one of those we can sneak this through when its in everyone’s interest to have all the facts before you decide how dangerous a system is .
The British pioneers of high T-tail aircraft in the 1950s developed powerful compressed nitrogen stick pushers for the BAC 1-11 and Hawker Sidely Trident since both of these aircraft could suffer from a super stall. These stick pushers were powerful enough to over power the pilot so great care was taken with sensor redundancy to prevent false triggering. There was an over ride. As far as I can tell the B727 never had a stick pusher so Boing has no experience with this type of device which may explain its cavalier attitude to MCAS false triggering. The resolver or synchro technology used to transmit alpha vane position is really quite robust and relies on wound coils. Each alpha vane has two synchro Transmitters it should have been possible to detect an electrical fault. The whole system stinks. I don’t think grandfathering should be allowed anymore.
The whole issue of pitot static and alpha sensor instruments on both Airbus and Boeing is ectremely disconcerting from the point of view of redundancy and diversity. Failure of such sensors has repeatedly led to tragedies. I particularly find the almost exclusive use vane type sensors foolish. Having only 2 or 3 sensors is also inadaquete . The pressure null seeking sensor works in a different principle and is resistant to freezing. There are also vane switches on wing tip leading edge stagnation points and even distributed pressure sensor. Birds directly detect boundary layer separation by feathers lifting off.
No one at Boeing was around when the 727 was in its hey day.
They do have experience with 767 and FBW.
They can read
And that is aside from the logic busts involved.
When I read it was a single input to failure it was, they are out of their flipping minds. I would not do that with a non life safety system.
AoA sensor signal is “analog”. And analog signal requires proper “shielding and grounding” to prevent signal errors. AoA sensor itself may work fine and produce correct signal. But without proper shielding and grounding of connecting wires, the signal is corrupted along the way, and destination computer gets erronous signal.
It is quite like a wiring problem. Not AoA sensor itself but electrical connection from AoA sensor to flight computer.
In other words, AoA is fine but “wiring” to computer seems problematic.
You are simply wrong. The original AOA was found to be bad in the lab. Period.
The replacement AOA was not calibrated.
There are actually two wipiing circuit on that AOA shaft, totally independent of each other feeding different computers.
Both computers registered the wrong data, ergo the VANE itself was set wrong.
It was not in the circuitry, it was the AOA.
In the case not covered, only one was bad and it appears to have in-puted to the Flight Computer.
The non calibrated one imputed into both computers (the o0hter is a secondary system of some kind)
This is the same signature that the crashed Ethiopian MAX had, both AOA inputs bad and after takeoff, a bird strike would exp0alin that.
William. Your post makes some unclear jumps so at some points I don’t understand exactly what you are saying. So here is my question: Are you saying that sensor technology has evolved and that the pitot tube and vane sensors are archaic and unreliable and should not be a part of modern fly by wire systems? Are you saying the only reason they might be used now is because it allows manufacturers to use grandfathering as a way of getting around new certifications for what would be state of the art innovations?
Steve: Background wise:
AOA and Pitot while refined are original tech from early aircraft (Bi-plane tech)
They do have all sorts of issues.
Unfortunate, something that works the same is hard to come by, the 787 system was one of the few so far and its backup.
Both are very failure prone (and you don’t want to get into a Pitot calibration!)
There should have been a lot more work on replacements of both.
Sideline:
is the aoa sensor type max specific?
Why does rosemount apparently have quality/testing coverage issues?
Original part had issues.
The part from the repair/spares path had issues
Seems to be a common sensor that has been in use for decades. The C130 uses one.
how about the line of parts for Airbus FBW?
Anything different?
Uwe, fromPage 37 of the report .. the AOA sensor was previously on a 737-900ER (non MAX aircraft). It looks like they were not buying new sensors, but, saving money by refurbishing out of spec sensors.
===========
This AOA sensor was previously installed on the right side of the fuselage of a
Boeing 737-900ER aircraft, Malaysian registration 9M-LNF, which was operated
by Malindo Air. The AOA sensor had been removed on 19 August 2017 due to
maintenance write-ups indicating that SPD and ALT flags were shown on the FO
PFD during a pre-flight check.
=====================
Note that repairing and overhauling of expensive components is SOP, many parts used in maintaining your car will be such.
Needs quality shop of course, I had to coach PW’s ‘rotables’ administrator on that, but note that manufacturers err too – the AOA vane that was removed before the fatal Lion Air flight
Do note as well that this is a very common sensor, used for several decades. (The Rosemount name is back on it, having cycled through BF Goodrich IIRC, the new ‘Collins’ mush has chosen to go back to the original name. I have little memory of it on 707/727/737 but it was onboard the latter two for sure, the 707 had Rosemount pitot probes, IIRC the 737’s combined pitot-static probes were made by Rosemount. IIRC they had their own little wind tunnel for development. And now used on Airbus airplanes.
In Boeing’s response to the Indonesian Final Accident Report, they mention a few changes to the MCAS system. The one I’m most pleased to see is the returning the column override limit switches into the MCAS system. If the pilot has the column pulled back into his stomach with all his force, now MCAS should deactivate. If this one switch had been active in the two accidents, there’s a good chance, they wouldn’t have happened.
==========
Over the past several months Boeing has been making changes to the 737 MAX. Most significantly, Boeing has redesigned the way Angle of Attack (AoA) sensors work with a feature of the flight control software known as Maneuvering Characteristics Augmentation System (MCAS). Going forward, MCAS will compare information from both AoA sensors before activating, adding a new layer of protection.
In addition, MCAS will now only turn on if both AoA sensors agree, will only activate once in response to erroneous AOA, and will always be subject to a maximum limit that can be overridden with the control column.
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https://boeing.mediaroom.com/2019-10-25-Boeing-Statement-On-Lion-Air-Flight-610-Investigation-Final-Report
====================
Boeing finally gave in to the fact that the pilots must be allowed to fly the airplane.
I’ll be interested in how the lower speed pitch up tendency will be addressed for the Irish newspaper report made clear that it had to be fixed. Clearly now it won’t be. So it will be up to the pilots.
The article from the Irish Times is from today, but the story was last updated on June 2, 2019 from the New York Times.
Something wrong?
Nothing wrong .. the Irish Times reprinted the article in June .. from the original NYTimes article. Here’s a link to the original NYTimes article
The Irish times website has today’s date at the top of their web page. I wish newspapers would put the original date at the top of their articles, and also their location.
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https://www.nytimes.com/2019/06/01/business/boeing-737-max-crash.html
======================
Thanks Richard,
I read the Irish version, the name Forkner is not mentioned there.
The New York version is much more detailed, the name Forkner is mentioned many times. Then I got blocked because I don’t have a subscribtion.
What I think is remarkable,
the New York version is old, very detailed and mentioned Forkner. Something everyone involved with the matter should have read. But Dickson obviously did not know it, which made him write to Muilenburg for an explanation last week.
How is it possible that Dickson didn’t know the NYT article?
Also the BBC is blaming Forkner today.
Smells something here?
Leon, The press at large barely notices the JATR report. But, they see some type of smoking gun in a couple of pilots emailing each other after a day at work. (Julian really made me see this)
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https://leehamnews.com/2019/10/22/boeing-recaps-actions-ahead-of-earnings-call/#comment-286500
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The head of the FAA is worried about these emails, so much that he fires off a letter to Boeing? I will agree with him, that Boeing has been very tight lipped. I can only hope that changes after the ET302 report becomes finalized.
Tight lipped is not the word.
Aviation has had a latitude that if things are reported, charges are not filled in the so called interest of safety.
For Boeing to withhold documents is damning in and of itself (and possibly chargeable)
That the context is in issue may not be, but when you add in I Lied unintentionally (no such thing) and Jedi Mind Tricks? That is huge red flag the size of a PFD.
Wrong Info:
1. Putting out wrong info knowing its wrong is a lie
2. Putting out info you think is factually and is wrong is not a lie.
So add in Jedi Mind tricks and it biases it to what he meant, I lied but did not want to admits it, i.e. hedging.
Two admittance lend this to it was a lie. Maybe the software was not finished but it was doing the major part of what it was deigned to do (massive elevator degrees shift )
Is there something wrong. Am I missing something?
Specifically, the chief test pilots said in the report that the lower speed pitch up tendency had to be fixed. That’s why it went to 2.5° from 0.6°. They are rolling back on 2.5°. Some reports suggest all the way back to 0.6°. But 0.6° that wasn’t enough to fix the problem. Therefor no longer fixed. This means the pilots will have to deal with it.
I am by the way confused. Boeing are not giving specifics. So it’s all interpretation.
Of course you are confused. Rather than jumping to conclusions you need to get all the details.
What it really is amounts to if the 2.5 deg t was needed and why other steps were not done such as speed specific movement stab limits (not to mention the rest of the software hash up) and why this was not published and given to the FAA for review.
That is what the investigation is all about. FAA clearly did not feel it was needed so why was it implemented let alone so disastrously.
Of course Boeing is not giving specifics, their collective butts are on the line. They think that by holding back it will save them.
It will come out, its just going to take some time.
Clearly patience is not a newer generation virtue.
Rome was not built in a day and a good investigation takes a long time (much quicker to hose things up than it is to find out what happened)
When they say that the column can override, that could either mean that the elevator still has more authority than the stab at a certain setting after one activation of MCAS, or, it could mean that pulling the column back to the limit shuts off power to MCAS.
Ted, You’re making me pace back and forth again. I guess I read in what I wanted to read in to it. I hope they don’t consider the column overriding MCAS as the elevator fighting with the stabilizer. MCAS needs to be controlled by the pilot (an OFF switch) or redesigned to full FBW certification, because it’s flying the aircraft, if there is no OFF switch.
The safety review aspect, of whether a system is dangerous, hazardous, catastrophic etc, needs a review itself. Who designated MCAS as hazardous? Boeing or the FAA or both? I guess any system that controls a flight surface, needs full review any time there is a change. I don’t see anything being done so that this accident of design doesn’t happen again. More redundancy in the review process (i.e. more people looking at it) may help. As in the old time Boeing, monster, design review meetings.
Bjoern, I hope your coming articles on the Lion Air Accident Report will cover (all) three main contributing causes; (1) the design of part of the FCC (MCAS); (2) training – both related to MCAS functionality, but also to ‘modern pilots’ capability to handle upsets and fly manually (as dealt with in the NTSB’s note to the FAA); and (3) the quality of the maintence carried out related to the AOA failure and subsequent testing, but also Lion Air maintenance in general.
I guess the report will follow the spirit of IACO annex 13, – look for improvements, so as to avoid similar accidents, and not to much on finding ‘persons or organizations’ to blame. That is how it should be.
Finally, I have one wish to your editorial staff, when yo start a series of articles, please call the first one ‘PART 1.
I don’t think it will review all the causes, just focus on the stability side. That’s what the backgrounder series have been leading up to.
Should make a great book , putting all the material together
Svein:
I make a clear distinciton between what occured with the Comet and even Boeing early days with jets (lots of accidents) as to not undertanding what the faults are were.
They did not know and did their best. They failed and a lot of people died.
Boeing does know better (as does the FAA)
There should be an accounting in this case, this was all deliberate bad work or failure to do your job ( if all we can do is ruin their careers then so be it – the FAA should have stopped the move Boeing made to have the inspectors report to Boeing instead of the FAA)
Its also been too cozy a relationship that should have been stopped long ago and that was in the power of the FAA.
We have been over this before. They did know about fatigue, they did run test sections through pressurisation cycles, and previous pressurised planes had square windows/hatches as well. It just came all together at higher altitudes and quicker cycles along with some construction flaws. Boeing was still having fuselage fatigue failures in the last decade.
Of course it’s not a destination but a constant journey for improving aviation safety.
IIRC deH tested a nose section for stress but not a fuselage. (Nose being more complex structure).
Riveting method was a factor in the early fatigue, something to do with impact as method, using an air hammer backed by a metal bar is common, squeeze would be better but requires long arms.
No doubt there some design faults, pilot training issues etc. that should be solved relatively easily.
The way the MAX was designed and certified in the 2011-2017 period I find far more worrying. Reduced independency, congress pressure, lobbying, rulemaking and cozy delegation & cooperation easily defeated flight safety. To stay competitive.
A crusial topic, Boeing, Congress and FAA will go a long way to avoid, blind-eye. https://www.gao.gov/assets/690/683649.pdf
AoA is based on resolver which is absolute position sensor. Does it need calibration on the sensor itself ?
https://www.pprune.org/tech-log/616624-maintenance-lapse-identified-initial-problem-leading-lion-air-crash-8.html
Found an informative discussion on AoA.
take a look at the details of the AOA sensor- its mickey mouse
https://www.satcom.guru/2019/03/aoa-vane-must-have-failed-boeing-fix.html
one loose screw ( main drive gear ) can foul things up
I think my electric shaver has better construction and more reliable gearing
Its certainly old tech (is an A320 etc any different?). We saw what Pitot issues do on all aircraft but more prone on Thales.
Also keep in mind that the failure assessment of the AOA only dealt with its own failures.
It did not take into account a ramp hit, bird strike (Ethiopian ).
So like the Japanese cooking the geological data books on the Fukushima reactor design risk, Boeing cooked the AOA (or are allowed to) books and limited the data set to allow a vastly lower than real risk of
AOA failure.
BBC NEWS is blaming Forkner today:
There were revelations this month that employees had exchanged messages about issues with MCAS while the plane was being certified in 2016.
In documents provided by Boeing to lawmakers, a pilot wrote that he had run into unexpected trouble during tests. He said he had “basically lied to the regulators [unknowingly]”.
https://www.bbc.com/news/business-50177788
Final KNKT Lion Air Flight 610 Accident Investigation Report:
http://knkt.dephub.go.id/knkt/ntsc_home/ntsc.htm
Download Link to the final report
FINAL KNKT.18.10.35.04
Aircraft Accident Investigation Report
PT. Lion Mentari Airlines Boeing 737-8 (MAX); PK-LQP Tanjung Karawang, West Java Republic of Indonesia 29 October
http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/2018%20-%20035%20-%20PK-LQP%20Final%20Report.pdf
Thanks William, not it downloaded.
Parsing the report, what I find on Airspeed and Altitudes is what I would call sloppy but relativity close (a distraction which may have been enough for undoing)
The question is why was the calibration that sloppy.
I note that the PFDs attitude indicator was -1 on the Captains side (PF) and and 13 deg on the FO side.
What I am seeing here is a confluence of events that in league with the disastrous writing of MCAS 1.0 pushed it into unmanageable by some crews.
While it in no way relieves Boeing of any responsibility, it does reflect how these things cascade (or can)
I think the issue of sloppy maint and procedures is justified in being put on Lion.
I don’t know what the allowance is, but the PFD should be on zero with a digital display readout. I am willing to best I could easily set one on the old Artificial Horizon to under 3 degrees.
Feelings as a pilot are conflicted. Boeing created a disaster, but poor pilots and air operations also contributed. I am disgusted at both.
MCAS solved or not, the piloting and maint of Lion is an atrocity – its a wonder they don’t have more crashes.
It will be interesting on the tech level to see what Ethiopians looked like.
If some find that reprehensible, that is what techs do, we look at data, though I fully understand the human side of this (I lost my father when I was young due to a bearing installed wrong on a boat out drive system)
I suggest that the following boeing document will help to understand what Boeing believes re use of AOA
http://www.boeing.com/commercial/aeromagazine/aero_12/aoa.pdf
great illustrations and discussion
and also read
http://www.ata-divisions.org/S_TD/pdf/other/IntroducingtheB-787.pdf
about use of inertial system for independant air speed etc pages 35 to 45
Why is it, that Boeing / FAA expects pilots to respond in 3 seconds, (in this case, with all of the confusing alarms, bells, shakes etc, it took 8 seconds), yet, after a few months, Boeing issues their infamous AD, just handle it like a runaway stabilizer event, if these dozen things happen all at once, and make sure you read the fine print, because otherwise you could end up in a bad situation. And then after 6 months, and another crash, they don’t want to ground the plane to sort things out?
If they had put the column limit switch back in the loop, or rewired the stab trim cutout switch and put out new procedures, in the months between the accidents, there’s a good chance ET302 would not have happened. This isn’t Monday morning quarterbacking on my part. They had literally months to figure out a reasonable fix, and only came out with the runaway stabilizer AD. The sim tests they did originally for MCAS didn’t test for a bad AOA reading, even though they had thought of it. The sim tests for the runaway stabilizer procedure seems to have missed the stuck trim wheel as the sim didn’t match the real aircraft. The old IBM logo “THINK” seems to be needed.
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https://www.ibm.com/ibm/history/exhibits/vintage/vintage_4506VV2024.html
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I am far from an engineer, but I have been reading posts here religiously for the past few months. I have seen a lot of discussion of how to fix the logic of Angle of Attack sensor failure if you have only two sensors. And I’m not sure I ever read anyone suggest: MCAS will only kick on if the two sensors are in agreement about the angle of attack. At least to me, that seems so simple and elegant after all the stuff I read here. I know next to nothing, but before reading any responses from the cynics, it made me take my hat off to Boeing engineers (not to any of the greedy, incompetent executives who should go to jail for letting this monstrosity further develop and not using their engineers to produce a new, elegant, sleek, efficient and state of the art Boeing 15 years ago that would have put everyone else out of business).
Steve, Yes, that is one of the ‘safety’s that Boeing is putting on the new MCAS system. If the two AOA’s are out of sync by over 5.5 degrees, then MCAS won’t activate. That will hopefully take care of false triggering. Unless of course you have both fail at once, which has happened in cold weather (two out of three AOA’s frozen). So, is that ‘safe enough’. Meaning how often will two fail at the same time? You’re on the right track. Keep thinking up solutions.
So, if one AOA is giving a correct reading and the other AOA is giving a false reading, then the new MCAS won’t activate. Which means that, if the correct AOA is indicating truly excessive pitch, then MCAS won’t do the job it was originally intended to do, and there’s a risk of a stall. And that’s supposed to be “safe”? If Boeing’s answer is “yes”, then they might as well remove MCAS altogether.
So now we can all wait for the first serious incident / crash with a re-certified MAX due to stall on climbout…
Peter, Boeing still thinks that MCAS isn’t a stall protection system.
So, with that in mind, they aren’t worried about MCAS protecting the plane from stalling. They seem to be in a box. If you rip MCAS out of the plane, how does it fly? Originally it seemed to be truly a speed trim system, but, when the upped the power to 2.5 degrees in 2016, after test pilot Ed Wilson noticed poor level flight, low speed stall tendencies, then they made it into a stall protection system. But, they don’t want to admit to that. Not even telling the FAA about the change at the time. I’m not sure if they’ve even fixed the paperwork yet. It would be interesting to ask Ed Wilson what he noticed on that test flight in detail, other than “something was off” and needs to be fixed.
Peter, I’m with you. I put it this way, if MCAS turns itself off when there is a problem, what’s the point in it.
Richard, the report makes clear that MCAS is about stall. Page 252, second paragraph.
From the systems side of thing you do not see a “true” and a “false” signal. What you see is “signals differ”.
There is no further data available to indicate which of the two is the false ticker. {drumroll} enter the third sensor.
“… , Boeing still _thinks_ that MCAS isn’t a stall protection system.”
Boeing still _tries to present_ MCAS as not linked to stall prevention. purely cosmetic. … and a lie.
Uwe, I agree about the need for a third AOA sensor, together with a well-developed voting mechanism. If EASA does its job properly, it will demand this.
A lot of beating a dead horse.
Frankly it does not make any difference at this point if it was stall or speed trim or a trip to the moon.
How Boeing sold it to the FAA and how it got there is part of the investigation and will come out.
MCAS 2.0 is not 1.0 and needs to be assessed on the basis if its good and well done or not.
Transworld, not everyone has to wait for MCAS 2.0 to actually appear in order to discern that it will be intrinsically flawed. Extending your horse analogy, there’s also such a thing as a “non-runner”. An alchemist can try pouring Ganges water on tin to see if it will turn into gold, but a chemist will be able to tell in advance that that’s a waste of time.
Comparing Boeing with an alchemist, that’s a good one.
Congress should tell this to Muilenburg tomorrow.
Richard Davenport
If you are speaking of the A320 series crash caused by freezing of the AOA vanes, a key factor was that the AOA vane housing is not mounted flush to the skin, looks like the skin overlaps the housing, thus there is possibility of a thick film of water covering the rotating joint between housing and base of vane. I think the 737 installation is flush.
In that accident the pilots did not handle the situation well.
Whereas in the Lion Air flight prior to the accident flight, both pilots did well – the PF held attitude and thrust – standard procedure, figured out his instrumentation was bad, turned control over to F/O, they went through emergency procedures. They did have help from a deadheading MAX-qualified F/O in the jump seat. But the Captain did continue with the flight to destination, which is not wise (albeit more maintenance was available there). One omission is he did not log stall warning nor use of cutout switches (which one of the pilots returned to normal position once on ground), perhaps he thought the problem was not AOA but he still should have logged such a significant event as stick shaker.
Installing the sensor slightly raised moves it out of the airflow surface disturbance “skin”. i.e. it sticks into laminar flow. Better signal, less noise.
I don’t get your “water catch pocket” idea.
for the “vanes frozen return to owner test flight” washing the plane had not been done in the prescribed way. The “functional test” was done at an insufficient height and the crew flying wasn’t qualified to do that test to begin with. cheese holes.
Steve,
You are not wrong though there is a subtlety that is techy that requires some rougher control.,
So first, AOA agreement – it would work though you need parameters (can they disagree 1/2 a degree, one degree or??) –
Or as the current MCAS 2.0 is doing, if there is an AOA disagree, it just returns the MCAS off. There are also limits on how much it can move the stabilizer and it can only do it once per AOA alarm.
Yes Boeing pulled off an amazing feat in making the MAX competitive.
They also did some lethal work in letting MCAS turn into a killing monstrosity (yes that is loaded) when good common engineering sense said it should not be and the cure was lethal while an accelerated pitch up is not.
A great deal of pilot training is put to staying away from stalls and then a great deal (more so now) to dealing with a stall.
I am willing to bet I could get into a 737 and un-stall a MAX in 3 seconds or less with pitch up in full play.
Why? Because a stall response is simple MCAS or not, you put the nose down. Stall is no longer in play.
And the only time a pilo0t will see a stall in his lifetime of piloting is in a Simulator.
He might if he is a light aircraft flyer see them in training (check out).
The only time I have ever seen a commercial aircraft get out of whack to the point it could stall, the pilots had failed to fly on their instruments and got disoriented by a misleading horizon (that is why we have that big PFD display in front of you, all you have to do is put the wings level and the nose on the horizon and you are good) There are two backups to it (the backup system and the other pilots PFD)
So the Boeing aerodynamic engineers did a fantastic job and the software engines undid all of with a very small bit of horrible programing.
” So the Boeing aerodynamic engineers did a fantastic job and the software engines undid all of with a very small bit of horrible programing.”
Actually the programming did exactly as designed – so who was responsible for changing the values and NOT telling anyone?
That is a spurious argument. The software was not designed or intended to kill people, it did that as a result of stupidly and failure.
That it worked badly is not as deigned but a major screw up in implementation and the quality assessment process that did not take place.
>The only time I have ever seen a commercial aircraft get out of whack to the point it could stall
Here is a very near stall in the exact scenario MCAS was originally designed to mitigate. A high speed turn at high elevation.
https://australianaviation.com.au/2019/03/atsb-releases-final-report-on-qantas-747-stick-shaker-incident/
I get the impression that Boeing paid GE several billion dollars to develop a more aggressive hot section for the B737 LEAP 1B to compensate for the larger fan diameter of the A320 LEAP 1A. The question is what kind of contract is preventing GE from applying the same tech to the LEAP 1A.
Airline mfgs negotiate how much money the Engine mfg give them not the other way around.
…”Because a stall response is simple MCAS or not, you put the nose down.”
Not a particularly savory course of action when the plane is near the ground. You might want to re-think placing that bet…
Think that Boeing SB was waiting for FAA approval before issue, the FAA was delayed by the goverment shutdown, then ET302 happened.
Even if Boeing had recommended grounding the FAA was closed and could not have acted. One can argue that all aircrafts with FAA TC should be grounded under FAA/US Goverment shut downs. Just like when an aircraft type engineering office is closed then its Airworthiness cannot be maintanced and the fleet is grounded by the Airline or Air Force.
Boeing should have done like SW Airlines did and offer to pay the FAA to stay open during the shutdown (grin).
====================
https://simpleflying.com/southwest-airlines-government-shutdown/
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https://www.faa.gov/news/press_releases/news_story.cfm?newsId=24314
FAA revokes the repair certificate of the instrument shop that Lion Air was using to repair AOA transmitters. Failure to maintain records documenting work performed.
And Lion Air maint itself?
Ugly all the way around. And Boeing triggered this into lethal with bad software.
TW, how many links of the single chain broke? How many didn’t have dual links? It is ugly all around.
My brief read of the Indonesian investigative agency’s report is that many things went wrong to generate the crash scenario. Primary among them was Boeing’s design failure, but it was far from the only contributing factor. As was suspected based on the initial reports, although that line of analysis was shut down by the “Boeing Must Be Destroyed” contingent.
Much respect to the Indonesian authority that did a thorough job of following where the facts led.
The apparent deficiencies (bad design, certification requirements circumvented or explained away ) exposed for these crashes completely unlinked the airline specific insufficiencies enumerated and the manufacturer misdeeds.
Boeing should “own” its blame though they haven’t accepted that yet. Still trying to squish out. “Dog ate my homework” childish behavior.
“” Failure to maintain records documenting work performed. “”
Boeing did that thousand times. What did FAA do then?
A Iovi vs. Bovi thing :-))
Hard to believe Boeing will still pay out a bonus to top executives like Muilenburg this year given everything that has transpired. I would expect a responsible Board of Directors to change the compensation rules. Have these people no shame?
https://www.seattletimes.com/business/boeing-aerospace/no-bonuses-for-white-collar-boeing-employees-this-year/
No its not hard to believe.
Its how Corporate America works these days.
Its all the scum welfare people who need to buck up and be held respisnbile.
Kind of like Bombardier. They deliver a plane years late, the stock is, oh, around a buck and a half, and the executives think they’re gods. The Wells Fargo guy, maybe got 100 Million to go away. These stories go on and on. A California power company filed for bankruptcy, and gave 350 execs bonuses.
It’s about as bad as an accident investigation report can be.
Pretty much everybody who could just plain fouled up.
1) Boeing created a grossly deficient MCAS design and concealed MCAS’ existence, then FAA lack of supervision allowed certification when it shouldn’t have.
2) Boeing (through a subcontractor) inadvertently disabled the “AoA Disagree” error indicator & message, then themselves decided it was minor enough to wait until the next year’s routine software upgrade.
3) Lion Air put an inadequate copilot in the right-hand seat (“the FO’s training records that showed several comments indicating that the FO had difficulty in aircraft handling. The Lion Air policy for such deficiencies was that the flight crew would be treated with additional briefings or rehearsal. The reappearance of difficulty in aircraft handling indicated that the treatment was not effective”)
4) The outstation line maintenance engineer (an employee of a subcontractor) almost certainly didn’t test the AoA indicator he replaced. It was faulty but he never tested it and …
5) The maintenance organisation that repaired the AoA indicator was using unsuitable and inadequately documented equipment to calibrate the repaired AoA indicator. They shipped one out that was about 20 degrees misaligned. The FAA (a different part of it) never noticed the repairer’s non-adherence to the FAA’s requirements.
6) The pilot of the previous flight pressed on when he should have turned back, so the repair required was done at an outstation, rather than main base. He also didn’t write up the fault completely – partly because the “AoA disagree” didn’t come on [see 2)], partly because he didn’t know about MCAS [see 1)], partly because …?
So many slices of cheese, so many gaping holes.
🙁 🙁 🙁
The accident report took the view that the only thing that needed highlighting in the synopsis was MCAS. The detail then set out human failure, but that is humanity.
With regard to MCAS, the accident report simply made clear that it does not have fail-safe redundancy. It also made clear that the purpose of MCAS is stall protection not speed trim.
So it comes back to this, is MCAS a primary control system or a secondary control system? In other words is it necessary for the airplane to fly safely? For the regulators to answer.
My only disappointment with the report is that it doesn’t state when MCAS engages, unless I missed a page. But we now know that it engages on the basis of AoA and Mach number. The AoA only needs to be elevated, whatever that means and the Mach number doesn’t need to be high. But why isn’t altitude part of the decision to engage MCAS?
Excellent report
Oops. Mach number varies with altitude. Too early in the morning and I’m more interested in the Rugby
Actually mach ( re speed of sound ) varies with temperature, which absent a storm or similar varies with altitude. So for a constant mach, the ‘mph’ varies with temperture.
So 0.2 mach = 150 mph approx on a ‘ standard ‘ day ( 20 deg cent or 68 F )
0.7 mach = 530 mph approx
And in simple flat plate against airstream, aero force varies as square of speed. so if 150 mph = say 1000 lbs force, then 300 mph = 4000 lbs force.
Noter I realize many here know the above general relationships, but some do not. The above then becomes a simplified explanation as to why the manual trim wheel does not work well at speed IF significantly out of trim.
Forgot to add that at 40000 ft mach .7 = approx 460 mph due to temperature of approx minus 56 degrees C
this gets the MCAS numbers in a bit of perspective as to speed, stall, altitude, and forces required- resultant
YMMV
I know Bubba. Very early in the morning, no cup of coffee and then Rugby. We won! And I can’t be bothered to write a long post.
Inexcusable. Mach number does vary as you said.
But may I ADD to your comment with regard to dynamic pressure. Yes in an idealised airflow the dynamic pressure is approximately the square of the speed. But it’s an approximation even in an idealised airflow.
But, wing/engine mountings are not idealised airflow. The wing/engine mounting is central to the problems of the 737 MAX.
Simple approximations don’t work in non-idealised flow.
Simple approximations have been replaced with computer fluid dynamics that typically use the Euler equations or more importantly the Navier-Stokes equations.
I don’t think Boeing ran the maths on the wing/engine mounting.
But then as you suggest, I don’t think Boeing ran the maths on manual trim, even the maths that say dynamic pressure is the square of the speed.
Human factors. TW, Mike Bohnet, sPh and others. Human factors.
I haven’t seen many people talk about the effect of the altitude of Ethiopia’s airport on all of this. The only exception is Dave Walker’s article on Medium.com
“Addis Ababa Bole airport is located at 7,625 feet — well more than a mile above sea level. This high altitude, combined with Ethiopia’s equatorial temperatures, imposes a natural performance penalty on all aircraft operations, causing a loss of engine thrust while also requiring aircraft to achieve faster ground speeds on takeoff. This morning the air was only 75 percent as dense as air at sea level. For those who are familiar with aviation terminology, the “density altitude” was 9,251 feet.
“Many airline captains can go through their entire careers and never once take off at a density altitude of more than 9,000 feet. Captain Getachew did it routinely …”
https://medium.com/@dawalk6/accident-timeline-of-ethiopian-302-ed20e33f900a
Almost everyone eyeball this fact – Addis Abbeba is hot & high. Personally, from a long time I suspect that was one of the reasons that among contradict warnings and unreliable airspeed they choose not to touch throttles, second reason – they were threw towards ground at low altitude by MCAS, third one – terrain around airport elevats progressively, so even leveling aircraft – you go towards ground actually. So not advised to roll back power in high & hot conditions. And you don’t have time and altitude to think things over. We’ll have to wait to Ethiopian report.
Steve:
Valid points well worth repeating. I knew about it but as a pilot I tend to discount it was it is just a known aspect of flying if you operate from fields like that.
Denver in the US is noted for it (mile high) Joberg SA is also a really high main field and some in South America.
I never had to deal with it really in my flying as it was pretty much a non issue where I flew.
But we sure ran the calculation as a lot of the US Western States small town airports it is major.
MCAS was never about “Speed Trim”.
but
MCAS uses the execution path that the “Speed Trim Function” provides ( i.e. electric actor working on the trim spindle).
IMU another reason why MCAS is “insidious”. On first blush Speed Trim and MCAS action appear indistiguishable, MCAS hides as Speed Trim action.
1. I don’t understand all the excitement of miscalibration of AoA sensor – for me doesn’t matter if it was miscalibrated, inproperly mounted, hit by bird / ramp / truck. Things happens but it shouldn’t bring the plane down by any mean, because in aviation we have something called redundancy and failure management.
2. “The star” of the crash report is MCAS, which was very well known fact and obvious from the start. So nothing new. Please hold enthusiasm about new MCAS version untill someone, eg. EASA which is only willing to speak about this publicly, will test MAX without MCAS and then with new MCAS. Then will see about MCAS. And they are other flaws / issues to address apart MCAS.
3. Best pilot could have worse day, and an average pilot could have average day, and a worse pilot could have a worse day – but they’re always 2 pilots – Captain & FO – the team is redundant itself. So pls don’t be excited about FO flight hours or previous performance. That day I think they both gave more then we could had expect.
I agree. The mis-calibration should have been irrelevant. Fail-safe redundancy was invented because of human factors.
The Captain appeared to be a bit of a genius with the electric trim wheel. Most of the time he appeared to know the exact amount of reverse trim to use in order to reverse the trim of MCAS, even though the flight deck offered no insight. The Captain appeared to have a bit of a crystal ball.
The FO wasn’t the equal of the Captain. But to the credit of the FO, at one point he did ask the Captain. But the Captain was distracted trying to work out what was going on. Soon after it was all over.
The problem is you guys don’t understand the process of what the investigation is intended to show.
Along with the most probable cause finding, you always find other aspects and issues.
In addition to the MCAS debacle, we also see Lion has maint issue and pilot issues. All those get addressed.
MCAS 1.0 is being addressed, along with the whole meltdown of how it got there as it was not just bad programming.
Pilots not acting the way assumed is a very important one that needs to be addressed.
How Simulator got programs wrong needs to be addressed (it goes back to the NG so its not a MAX related issue)
Sloppy PFD settings is also an issue as is sloppy calibration of the Air speeds and altitudes between the two sides (while not the cause they cause considerable troubleshooting)
Swapping to the FO would well be an issue with 13 degree disagreement on his PFD, already he will not have the nose where it should be.
Both PFD should be zero, how tight the speeds and altitude can be calibrated to should be there and not Creation their own alarms adding to the confusion while other issues are in play.
Nothing simple about it. Boeing is clearly the Most Probably cause but the other aspects put in their own as each was a distraction from the main issue.
Some like the change in the Trim Forces should never have been allowed and an investigation unto itself to see why that blew an Ocean Liner through the certification’s wall, major not miner issue.
347 people died and we want to extract every much as possible improvement from and for the system. Clearly its the least we can do as we can not bring them back.
Give it a break. You don’t understand.
A lot of the report addresses what is referred to as a functional hazard analysis (FHA). The pupose of the analysis is to categorise the hazard, the risk.
With regard to FAA regulations, many of the regulations are only triggered if the hazard is categorised as above a certain level. Consequently, FAA regulations can be by-passed by arbitrarily reducing the hazard, the risk. In simple terms, a major hazard/risk is arbitrarily reduced to be a minor hazard/risk.
That is what happened with MCAS. This was first confirmed by JATR and now confirmed by the report into the Lion Air crash. Expect it to be confirmed again in the Ethiopian Airlines crash.
Human factors must always be part of a FHA analysis. Indeed human factors are central to a FHA analysis. There is nothing unusual in the report with regard to human factors.
But I agree human factors do need documenting. It doesn’t mean that they should be elevated to avoid addressing underlying problems. The Lion Air crash report is very careful not to do that. It points the figure at MCAS.
Clearly the 737 MAX does have a pitch up tendency and it starts well below the pre-stall region of the envelope. This was confirmed by the JTAR report and now by the Lion Air crash report. It will be confirmed again by the Ethiopian Airlines crash report.
Give it a break. You don’t understand.
Well, someone doesn’t understand. Over the last 6 months a small group of LN commenters have advanced a series of arguments that if accepted in full would call for the shutdown and dismantlement of Boeing Commercial Aircraft. These calls have been so vehement and have so thoroughly infected the technical arguments the same set of commenters have made that it renders their judgement suspect. Now an independent investigative agency issues a report with multiple casual factors discussion and the “Boeing Must Die” response is that the entire report except the MCAS – a system already acknowledged as badly designed – can be dismissed. No agenda here!
I am still waiting for the technical evidence of the 737MAX’s fundamental aerodynamic instability. No links yet, but I am sure they will be provided soon.
@sPh
Again, give it a break. I have never critised the safety of the 787 or any previous generation Boeing airplane.
@sPh
Yes, the big question, what is the instability . The trrm ‘elevated’ is now being used. MCAS is activated at elevated AoA.
In english, ‘elevated’ is used as being less than ‘high’, and ‘high’ less than ‘extreme’.
But it’s inexact. Don’t like that.
With regard to the rest of your post. Give it a break. Boeing engineers do know how to build a naturally stable airplane. Never said anything else.
So I want to know what stopped them from doing it this time. My guess, and repeated guess, is management.
Philip:
I suggest you give it a break.
Lion has an abysmal safety record.
AF could not train pilots, should they have been shut down?
spH nor I are giving Boeing any break on the MCAS.
But there is an interesting bent there that Boeing is solely responsible for all the ills when in fact just plane bad piloting kills a lot more people than MCAS ever will (because its fixed)
spH like myself is tired of the uninformed conspiracy rantings about unstable 737s.
None of which is supported by Bjron who is an aviation engineer and more than worth listening to.
But AF can kill a whole wide body worth of passengers and that is just fine.
Or in Ethiopians case, pilots went disoriented and dumped a 737 into the Mediterranean killing all on board and that is ok, it was just a pilot mistake.
I got news for you, pilots kill vastly more people than any aircraft mfg ever did.
Pilots and maint operations are a day in day out ongoing problem.
The Lion report clearly shows (as well as their abysmal safety record ) that unless that is corrected, they will continue to kill people.
But that is fine, its only Lion doing the killing (or Air Asia or Ethiopian) as long as there is not a big evil (American) corporation to blame.
@sPh:
Your “observation” has no contact to reality.
What is demanded by all reasonable posters here is that “Boeing must Change its Ways”.
“Blame the pilot” is a long standing strategy brought forward by and/or others to the advantage of Boeing.
Certification wise 787 deficient batteries design had the same systemic underpinnings found around MAX MCAS.
You seem to go for “nothing to see, move on”. Boeing is “Holy Cow, untouchable”.
TransWorld
I’m sure Lion’s FO was a nice guy but he should never been in a cockpit and especially shouldn’t have been called at 4 am.
But how can pilots be blamed if MCAS was kept secret, if training was a one hour joke on an ipad, if other things changed from the previous 737 NG and some things didn’t work too. How about pilots who never flew the NG, how can they fly the MAX. Three seconds to respond and 100 lb on the control column.
This is all Boeing’s fault alone, especially after Sullenberger and others tried it and could do nothing too.
Put 100 lb around Muilenburg’s neck and see how he swims.
Leon, the Lion Air report makes clear what happened based on the evidence. The combination of bad A0A reading, bad MCAS behavior, and exclusion of MCAS from the flight manual, placed the pilots in an extremely adverse situation. Everyone here agrees those things were wrong, should not have happened, and need to be corrected
Despite this adversity, the captain had quickly worked out how to interrupt and counteract the MCAS cycling, even though he didn’t know what was causing it. This required his constant attention due to the continuous cycling of MCAS. But he was able to continue the climb to the requested holding pattern, so as to continue working the problem and figure out what was wrong. He did not issue a pan-pan or mayday. He didn’t see a crash as being imminent.
Then he gave control to the first officer, without comment or explanation. The first officer did not continue the captain’s actions to interrupt and counteract MCAS. The aircraft began a rapid descent based on the uncontested actions of MCAS, and crashed.
So with this in mind, it’s clear that the crash had multiple causes. Boeing absolutely has responsibility for the MCAS component, both the incorrect behavior and the exclusion from the flight manual. No question and no defense for those oversights. But these were not the only factors. As is always true, pilot skill also plays a significant role.
Boeing designed the MAX with the assumption that action to counter the failure shall not require exceptional piloting skill or strength.
@TransWorld
I think I understand quite well how the investigation works – everything shall be taken into consideration, every flaw or slip, even a smallest one and investigated.
I wrote about excitement among flying public that arose about miscalibration of AoA sensor.
@sPh
I also can’t wait MAX instability will be checked. But we’ll have to wait, until EASA will do it, but timing depends on Boeing readiness only.
Well seeing as instability is something that is developed deep int he fold of some minds that don’t understand aerodynamics is irrelevant of course.
Damn the facts, full speed ahead.
An A320 (and other FBW) aircraft cannot land and barley fly without the computers.
Now that is unstable. Passengers have to hope that all the bases are covered (like 2 out of 3 pitots ly9 and which ones ) or the whole scheme goes into the trash.
Credit Boeing with going another step in alternative speeds on the 787.
No, that does not undo the hideous MAX 1.0 work, but it says something too about the future.
@TransWorld
From where you have had draw the idea that FBW airliners and or A320 can’t fly without computers? Stunning. Maybe you mistaken an FBW airliner with a FBW jet fighter?
@TransWorld
You are the prince of unsuitable comparisons.
“An A320 (and other FBW) aircraft cannot land and barley fly without the computers. ”
A 737 can’t fly or land without the steel wires and push rods coupling yoke to control surfaces.
Which failure rate is lower?
Can I say this. Awhile back I offered a theory with regard to elevator inoperability, inviting everybody to shoot it down. It didn’t work. My theory was a guess but I didn’t get the facts. I want the facts.
The good thing is we do now know most things about how MCAS works. But and it’s a big but. We still don’t know when it activates. Yes we now know it activates on the basis of AoA and Mach. But we have not been told the numbers. So we know how but not when.
So we still don’t know when the pitch up tendency starts. Perhaps LNAs articles should take that into account. We are still guessing.
One way or another Boeing are going to have to own up.
Philip, there’s no flashing light saying MCAS active. It’s hidden within all of the normal speed trimming. So, the trim wheel moving, to a pilot, means either the normal speed trim function is running, or MCAS is active. It doesn’t make a different sound. Just the wheel turning, as it does multiple times a flight. Maybe there should be an alert .. MCAS ACTIVE sounding or flashing lights? How many times in the past has MCAS activated? No one knows? Are there any records? It’s hidden in plain view. How does a pilot know when MCAS is active?
How does he know when MCAS is happy and has been reset? There are no indications.
@Richard Davenport
I am asking myself from a quite time about it – how many times MCAS activeted during all flight. Is a true that it’s operates only in far corner of the envelope, as Boeing says, or this is only a Boeing tale and it activate on daily basis. Boeing says nothing, so will have to wait until EASA will check it.
Pablo, Maybe there’s another way to find out?… There are some old MAX simulators around. Not many, but, some. Depending on how accurately Boeing’s sim data packages are, you could ‘fly’ an old simulator, to see, but, you’d have to somehow be able to differentiate between the normal trim signals and the MCAS trim signals. That would take some data analysis of the data package. But, I’m assuming the answers could be there also. Some sharp sim tech at the simulator maker should be able to break out the different logic paths to see what the actual MCAS programming thresholds are. I assume EASA would have to formally request this, as there’s probably some legal agreements between the sim maker and Boeing about who own’s the data, and/or how it can be used.
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https://www.cnn.com/2019/03/28/africa/ethiopian-airlines-boeing-max-8-simulator-manual-intl/index.html
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Amazing, some of the world true experts have weighed in and we have two outstanding ones at our finger tips (Peter Leme and our own Bjorn) but its two individuals who have no aircraft experience of any kind that have sleuthed out the Evil instability and MCAS working all the time.
I guess the US did not land on the Moon in the Summer of 69 after all, it all was a hoax.
TW,
2016, Boeing Pilot Ed Wilson lands after a test flight and tells the engineers that they need to fix the low speed stall problem (we have no real details). They change MCAS at the last minute and don’t inform the FAA. They don’t tell Airlines about the system at all.
Then, the first crash happens and we find out from Boeing, that there is this thing called MCAS that will move the stabilizer at .27 degrees per second, up to 2.5 degrees and 9.26 seconds at a time, which is news to the FAA and the world. Aviation folks gasp at the speed of MCAS. Speed trim isn’t supposed to be that fast and powerful for that long a time. Boeing says it activates when the flaps are up, and the autopilot is off, and the angle of attack is “high”. It should shut off, when the angle of attack is “sufficiently lowered”. Other than that, I don’t think the world knows the values of ‘high’ or ‘sufficiently lowered”. Boeing should. But, they aren’t saying. They’ve been working on a software fix, and seem to be working on a dual channel reconfiguration of the computer system, and wiring in the other AOA into MCAS. which is not trivial. But, Boeing has not described the pitch up problem or MCAS trigger numbers. Maybe it’s trivial, but, with Boeing making these changes, it sounds like without MCAS or some other change, the 737-MAX isn’t certified. It looks like Boeing is taking their time to make sure thing are fully redundant because MCAS is a primary control system. Why the stab trim cutout switches were rewired is very puzzling, Peter Lemme is also scratching his head about that change. Someone at Boeing went to the trouble of changing the switches. Have you ever heard of a planes control system, major or minor, not being described to an airline in some repair or flight manual before? It’s baffling. That’s why there’s so much speculation, because after a year, we still don’t know simple facts about MCAS, like what is the ‘high’ value that it triggers at, and any real numbers or a description of the pitch up issue. Bjorn has some good ideas on the problem, but, no numbers to go with them. That’s why I’m frustrated. Boeing has been keeping the details, even a summary, of this pitch up problem in the dark for so long. And it obviously is serious enough for them to spend over a year redesigning MCAS and associated fixes.
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https://airlinerwatch.com/content/images/2019/03/737NG-vs-MAX-engines.png
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Page 197 of the report (MCAS Function)
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To incorporate MCAS, the basic column cutout function had to be inhibited during
the MCAS activation. Pulling back on the column normally interrupts any electric
stabilizer aircraft nose-down command, but for the MAX with MCAS operating,
that control column cutout function is disabled.
============
Can anyone explain to me why MCAS needs the column cutout function to be inhibited? Why MCAS needs to override the pilots commands? Why MCAS takes control of the aircraft, leaving the pilots powerless? Why would you design a Boeing aircraft that way? MCAS is not FBW certified. Boeing’s doctrine has been the pilot has ultimate control of the aircraft. Did I miss a memo?
Richard, the thinking behind that was that an impending stall situation might be created by a pilot pulling back too much on the column, without anticipating the MAX’s accelerated pitch characteristic at high AoA. This is the situation that MCAS was designed to address and avoid. So if MCAS was disabled by pulling back, it effectively cannot fulfill it’s function.
I don’t know how Boeing has addressed this, but my guess was they would not establish the column cutout switch, but would instead alter the MCAS software so it doesn’t have the authority to override the pilot’s elevator inputs. It should only serve to counteract the accelerated pitch tendency at high A0A, which is all it was ever meant to do. To the pilot using the control column, this should feel like the MAX does not have this pitch tendency, it would feel like a more linear pitch behavior, which is what the pilot is expecting and is similar to the rest of the flight envelope.
If MCAS had been properly designed and implemented, this would be the desired behavior. Again you can look to military versions of MCAS that do behave like this. Why the same design was not used on the MAX, we still don’t know. I hope this will be addressed in the investigations.
@Rob
Boeing would disagree with you because MCAS is not an anti-stall system, its only augmentation system, giving MAX only NG feel. So what are talking about man? 😉 [sarcasm intended]
I just look at what MCAS does. MCAS was intended as an augmentation system, to compensate for the accelerated pitch tendency at AoA (the non-linear portion of the pitch curve Bjorn has discussed at length). In the absence of augmentation, the risk is that a high AoA maneuver could lead to an impending stall.
So I think this is a distinction without a difference. You could also say that MCAS helps the MAX feels more like the NG, that is also true. Whatever Boeing says and whatever alternative opinions are expressed, MCAS does what it does, and that should define it.
Rob, The problem is that an AOA failure on a 737-MAX has proven to be deadly in 2 accidents. AOA failure’s shouldn’t be this dangerous. AOA’s do fail. But usually they are a nuisance. (I picked out three occurrences below)
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https://www.avherald.com/h?article=4b4f3b2b&opt=0
https://www.avherald.com/h?article=49931cb1&opt=0
https://www.avherald.com/h?article=40b278ab&opt=0
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All dealt with without crashing. The 737-NG has a speed trim system but, doesn’t have MCAS. Boeing was using MCAS in a role (stall prevention) that it wasn’t designed for.
We’ll have to wait for EASA’s tests to find out how serious the stall problem is (does it need 2.5 or is 0.6 enough?) and how Boeing will deal with it.
Rob, If that truly is the case, then Boeing needs to certify MCAS as a true FBW primary control system, with all of the needed redundancy. And a few questions raised about why this wasn’t done in the first place. (I don’t doubt that this may be the case) Hopefully EASA will find the answer. I don’t have any confidence at all in the FAA, as they don’t even want to talk to the designated FAA reps directly, or have any say in choosing them any more.
I agree that MCAS should have received much more thorough certification. The reasoning behind not doing this, was that the initial MCAS affected a small portion of the flight envelope that most pilots and aircraft would never experience. But that became invalid when the function was expanded to the low-speed case, and granted much greater authority. If it was capable of fully deflecting the stabilizer, then that is bordering on FBW and needs similar verification and safeguards.
No, it just has to be done right, not sloppy half assed per the way Boeing did it.
MCAC 2.0 is totally different and people really should read the list of corrections before commenting. .
The MCAS 1.0 horse is dead, lets quit beating MCAS 2.0 with the MCAS 1.0 stick when MCAS 2.0 is the topic for going forward.
How MCAC 1.0 got to the major movement (and no speed relation) it needed is a totally different story than what MCAS 2.0 does.
So, keep MCAS 1.0 assessment with 1.0 and not 2.0.
If you are going to talk 2.0 don’t use 1.0 at all, its not the least bit relevant (other than MCAS is active all the time in my car and unstable conspiracy theorists aside) – those I invite to visit area 51.
As far as I know no regulator seen new MCAS version as finished product. Then no regulator has tested MAX stability issue without MCAS. Too early to assume anything.
Rob,
Military versions of what you are talking about have big control surfaces to stop the acceleration. The F22 is a very good example. It has a very large pair of all moving stabilisers.
That’s why Boeing shifted to the stabiliser on the 737 MAX to control the moment curve. The elevators can’t do it. But they should have upgraded the stabiliser to an all moving stabiliser controlled by the yoke. In the alternative they should have built a bigger stabiliser with bigger elevators.
Many want a conversation that says the 737 MAX has a typical moment curve. In other words what is all the fuss about. I would agree. What is all the fuss about, if the moment curve is typical? But then if the moment curve was typical MCAS wouldn’t be necessary.
I don’t think the moment curve of the 737 MAX is typical, I think it is atypical. Atypical can mean one of the following or a combination of the following. No part of the moment curve is linear. The linear part of the moment curve is very steep. The non-linear part of the moment curve starts early. The non-linear part of the moment curve involves steep accelerating.
I emphasis that steep linear moment curves are not a good idea.
Boeing won’t tell. EASA are demanding to know. EASA want to fly the 737 MAX without MCAS.
Philip, the military MCAS system I referenced is on the KC-46 tanker. That aircraft is based on the 767 has similar control surfaces to the 737 MAX. In the case of the tanker, the pitch stability curve can be altered by shifts of the fuel load at high AoA. This is a slightly different problem than the MAX, but the function and intent of MCAS is the same. And it was much more thoroughly developed.
As far as the stabilizer vs elevator, the elevator is under the pilot’s control, so the stabilizer is used for trim. Those functions are intentionally kept separate for safety, to make sure the pilot always has full elevator authority available. That is one of the problems with the MAX MCAS, it didn’t operate in a way to preserve elevator authority. Excessive deflection of the stabilizer could and did result in extremely high control forces on the control column and elevator.
The all-moving stabilizer on the 737 is used for trim because it results in increased fuel economy. The large area of the stabilizer requires only a small defection to provide trim forces, which reduces drag since trim is in effect during the entire flight.
The moment curve (pitch stability) has been discussed by Bjorn at length, he indicated that the behavior is not exclusive to the MAX. Aircraft use various means to address the non-linear part of the curve. Boeing used MCAS, Airbus embeds that function in the FBW system.
Almost all of the recorded 737 MAX flight hours have been flown without MCAS. MCAS activation would appear in the flight data. The test flight data that was used to develop MCAS should be available from Boeing. If the EASA want to repeat those tests, that should be possible. It should be possible to disable MCAS in the simulator as well.
Thanks for the clarification. So to speak.
With regard to Bjorn, he’s guessing. He doesn’t know the moment curve, you don’t, I don’t.
Airbus don’t use atypical moment curves. That is a lie and a total lie. All Airbus airplanes are naturally stable. They have typical moment curves.
I do admit that Bjorn does claim Airbus do what Boeing do. Not true. Airbus don’t do what Boeing do. They can’t be further apart. It’s a lie to suggest Airbus do what Boeing do.
Tarring Airbus with the brush of Boeing doesn’t work for me.
But as Scott said to me a long time ago, it’s his blog.
Again. I don’t quite understand all of the technical implications of this discussion. Does one of the core issues involve an attempt to create what looks like a “fly by wire” system for a stridently non-fwb aircraft or system? Doesn’t this produce a whole lot of unexpected complications? Isn’t this one of the issues? It’s my impression that while the 767 might not be entirely fbw, it has, at least, a fbw back up as part of its redundant systems. Would this make it more amenable, or more compatible with a FBW-like patch such as MCAS? Are we talking apples and oranges?
What a hoot, Bjorn does not know the true aspects of this?
Best laugh of the week.
I hate to break the news to people who do not know what they are talking about, but talk about it anyway.
Steve:
You hit the nail on the head.
Its all a system and you can’t do bits and pieces. The agenda here is to ground the MAX for all time no matter how well it can be made to work. Call it FBW is the only thing that is ok (but ignore all those pesky pilots killing plan loads of people, that is fine)
I am still howling at Bjorn is only guessing. I assume Einstein was only guessing at E=MC2!!!!!!!!
His guess you can take to the bank.
Philips, not even at sea level, I would put it at the bottom of the Marianne’s trench.
Steve, the notable thing is that the military version of MCAS already had the features that Boeing has now added to the 737 MAX MCAS. The military immediately looked into this after MCAS was implicated in the 737 crashes, and were satisfied that the same problems didn’t exist in their version. The KC-46 has had its own development problems so I’m sure they wanted to be sure.
My basic point was if Boeing can do this correctly for the KC-46, they can for the 737 as well. The question is, why didn’t they do so in the first place? I hope that question is addressed at some point.
@TransWorld
Nor Bjorn, nor you, nor EASA, nor anybody, only Boeing knows, what are stability aspects of MAX. So he is guessing, we are guessing. EASA will finally test it.
The U.S. Military-Industrial-Congressional Complex at its finest!
(Sarcasm mode on)
Boeing Shaped a Law to Its Liking. Weeks Later, a 737 Max Crashed.
https://www.nytimes.com/2019/10/27/business/boeing-737-max-crashes.html
Shouldn’t the New York Times and its investigative staff — shouldn’t the Fourth Estate — have written an aggressive investigative piece about this horrific piece of legislation before it was crafted, voted on and signed? Huge, wealthy corporations such as Boeing that advertise and sometimes pay the bills of a floundering industry (newspaper journalism) have a tremendous amount of power. The journalistic bar is held very, very high before critical stories about them are allowed to move past the editor’s desk.
What ? A paragraph or two in legislation thats hundreds of pages and lobbyists fingerprints everywhere.
You need to know what ‘news’ is . Something new has to happen first as a hook for events and background to be added. The FAA is mostly a non news area, unless its to do with airport delays etc.
Boeing is a business to business company, no passengers pay Boeing for a ticket, so it doesnt advertise like you think, especially with the type of paper – a Journal of record- the NY Times is.
Actually, companies like Boeing advertise all the time. Investigative reporting doesn’t have a “new” element. Beat reporters regularly read hundreds of pages of reports.
A hazardous failure condition is >1/10million flight hours.
Boeing said they found 25 failures in 240 million hours but didn’t described it hazardous.
Boeing lost it.
What about the FAA, maybe drank too much coffee.
FAA caved to Boeing, plane and simple.
Yes in the MCAS 1.0 there is a really ugly nasty viscous bit of work involved by Boeing.
But some of that is set in FAA reg even before this that real world failures are not how they assess and they should be (bird strike, ramp rash , no calibration etc)
Coffee has nothign to do with it nor does dope.
Its an ugly part of the system that we don’t have our legislatures keeping an eye on and stopping. That gets into a whole different area.
TWA ” FAA caved to Boeing, plane and simple.” is just partly true, The biggest IMHO contibutor is the change made in DER versus ODA game. The DER gamealllowed FAA-Boeing paid employees to go communicate directly with FAA and were insulated from Boeing management fairly well. When SPEEA struck in 2000-2001, Boeing at first said no big deal, who needs the engineers to ‘assemble’ airplanes, etc. That was for the most part True. But when the DER ( engineers ) walked out- Boeing mismanagement found out that ‘ NO nerds NO birds ‘ had meaning.Boeing could build the planes, fly the planes( maybe ) but could NOT deliver without certain DER signatures. This little oopsie enraged management and started the ‘ move’ to ODA, wherein the same DER types had to route all thru ‘ Boeing systems- management’ by whatever name.
And management bonus was based on making the numbers and schedule.
As the NYT article covers- the rest is history. 777 was the last DER airplane on first flight,. The history of 767 tanker in 2001-2-3 and 787, and later versions of 737, and kc46 and 747-? and other boondoggles too numderous to mention here eventually resulted in the MAX-MCAS.
But mcnearney still enjoys his golf game ..
This is not exactly new and the point is?
You are welcome to go to Mr Mcnnearniey golf course and take his balls away from him.
Do I get a choice of
Tweezers,fingernail clippers, garden shears,or dull bowie knife, or a small stretchable O ring used for steers ?
Do I need FAA or Boeing approval ?
On October 25, Peter deFazio, Chair of the House Committee on Transportation and Infrastructure (Congress), commented the Lion Air accident report, saying ”And I will be introducing legislation at the appropriate time to ensure that unairworthy commercial airliners no longer slip through our regulatory system”.
I was under the inpression after the Paris crash of the McDonald Douglas DC10 no more hand shakes over certification of aircraft or A.D,s it seems like ground hog over again.
That is what has me just incredulous.
Suddenly the FAA has lost its credbility ?.
Boeing and the FAA have been doing this for a long time.
I guess it gives the other AHJs cover for suddenly coming to realize how evil the two are (so they are not exposed as to how lame they are)
DC-10 was one and the 737 Rudder Failures were another.
The 767 valve could have been much worse but thanks to Niki Lauda who single handedly (thank you very much) got that dealt with . It would take someone with the focus, technical knowledge and resources to do what he did there.
I guess when you come late to the table you don’t know your history. That is what old farts are good for if the newer generations actually have the grasp to listen instead of thinking they just invented the wheel.
” The 767 valve could have been much worse..”
Did you mean 737 rudder hyd servo valve ??
Don’t hold your breath. The Senate has to co pass and with its makeup, that is not going to happen.
At best they do fix it and then the chipping away begins.
Maconda mandates are attempting to be overturned.
Wall Street and bank limitation are already undermined (with a big endorsement from both sides)
What we need is a rule that say you can muck with this for 100 years once we have got it under control.
Not so . The FAA Authorisation Act has to be done every couple of years. Thats when the last changes were made and can be ‘unchanged’ in the next one. Without a new authorisation or at least an extension , the whole FAA apparatus could grind to a halt.
Its the American way of doing things
No, it does not have to be. Its just the way it is being done.
But yes its our way of mucking things up.
Brexit anyone?
You’re exactly right about the Macondo well regulations. After the blowout and oil spill, regulations changed to say that the blowout preventer must be capable of controlling the well in all circumstances (most cannot, they are only designed to control a kick).
Although this spurred major improvements in preventer technology, and resulted in preventers that could control a blowout, the industry was unhappy about the increased costs, and said it was unfair because the vast majority of wells do not blowout. Yet there are still multiple blowouts every year.
So the older, less capable technology will become legal again. This seems crazy given the forces that are unleashed in a blowout, not to mention the pollution. It’s like rejecting safety in an airliner because the vast majority of flights do not crash.
Finally it is leaking out.
“An examination by The New York Times, based on interviews with more than 50 regulators, industry executives, congressional staff members and lobbyists, as well as drafts of the bill and federal documents, found that Boeing and its allies helped craft the legislation to their liking, shaping the language of the law and overcoming criticism from regulators.
In a stark warning as the bill was being written, the Federal Aviation Administration said that it would “not be in the best interest of safety.””
Thanks free press, NYT. Boeing, Congress and FAA have been trying to ignore / dismiss this root cause for months.
Boeing was meeting regulations they crafted themselves and let Congress approve them. Congress members getting campaign support from Boeing. Congress setting, cutting FAA budgets, setting goals. Operation “Streamlining”
Read the 2017 GAO-17-508T report and latest JATR report in case of doubt.
Nothing new, we have a problem and have had one for a long time.
How to solve it is not easy, may not be doable as it gets deep into Politics that we can’t discuss despite the relevance.
Yes, but … that bill was not a root cause. The bill was passed shortly before the Lion Air crash, and by that time the MAX had already been certified.
What the bill does, though, is even further reduces the strength of the FAA oversight, and allows companies to influence FAA staff by providing input into their performance reviews.
Incredible.
In the GAO report it becomes clear this process was pushed hard from 2011 already and all the FAA re authorizations since then.
The ARC , Aircraft Certification Process Review and Reform
Aviation Rulemaking Committee (ARC) has been succesfully “streamlining” the certification process, pushed by sponsored opportunisist in congress, with little aviation safety knowledge. Now the chickens come home to roost.
I missed this part, from what they are describing, the 2.5 deg is low speed related and there is some reset curve to lower value as speed increases
https://www.flightglobal.com/news/articles/boeings-mcas-test-did-not-simulate-other-cockpit-ef-461815/
Steve:
This is a good more detailed look from engine mfg at supply chain issues
https://www.flightglobal.com/news/articles/cfm-returns-to-on-time-leap-production-preps-for-7-461821/
Each area be it hydraulics, electrical , fasteners and materials faces the same issues and sometimes more (just castings is not all there is to it, P&W came out with new blade type mfg, but then found out the reject rate was higher than they thought it would be and had to get more proeui9on centers to make more to accommodate it)
Hey speculators and xenophobes, observe that the AOA vane was designed and made in the USofA, and the repair shop is in the USA. So obviously US agencies should have a strong interest in it.
Indonesia trusted the US’ agency and got what seems to be a good analysis of the vane removed from the accident aircraft before it crashed, and of ways the test equipment could fail to detect an offset.
And keep in mind that Ethiopia has closer ties to northern Europe than to North America. France of course may have some knowledge of testing the AOA vane as it is used on Airbus aircraft, likely many are repaired in Europe (perhaps even by Lufthansa).
As for why the Indonesian investigators believe the AOA vane on the fatal Lion Air flight was misaligned despite not recovering the vane, I haven’t had the time to crawl through everything but note:
– it was obviously in error
– there was a test at the repair shop in FL that arbitrarily used something like 22 or 25 degrees offset to evaluate the shop’s test setup (the report says arbitrary but isn’t there a 22 degree theory of possible error from one failure mode? (Perhaps from Peter Lemme months ago.))
– perhaps there is data like FDR comparing left and right vanes.
Does seem to be a conclusion from best available information, but I repeat that it obviously was substantially in error for whatever reason (could be bird strike though suspicious is misalignment internally).
Certainly much learned about those AOA vanes by the investigation, including manufacturing them right, shop test, etc.
Keith, Here’s the link to Peter Lemme article mentioning the 22 degrees on the AOA
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https://www.satcom.guru/2018/12/angle-of-attack-failure-modes.html
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AND Transworld, I say mmmm – didn’t Boeing provide the messages to DOJ when they discovered them? If so, because of suspicion of false statements, isn’t that technically the purview of the DOJ not FAA? Would have been nice for either or both to advise Boeing they had some correspondence, if it was legal to and sound investigative practice.
BTW, related to defining what a lie is, there is law (whether actual law or ‘case law’ (in the British system which the US also uses) that does not exempt you if you _should_ have known a claim was false. That’s the case in defamation law and another field I forget. It will vary by country and vintage (Canada’s defamation civil law was substantially changed by a court decision a few decades ago). DOJ is of coures for criminal activity, defamation is civil law.
You are addressing a case where the uttterer genuinely believed what s/he was saying – with good reason, but erred.
Just a reminder – Tomorrow Tues 29 Oct. Boeing CEO will be testifying before congress hearing for two days. Should be available on CSPAN- free tv
Seattle times and WSJ both have some very revealing articles
There seem to be more than a few misconceptions regarding 737 MAX stability and MCAS swirling around LNA’s comments sections in the past year. This is happening despite Bjorn’s thoughtful and thorough series of articles on pitch stability explaining these very issues and the MCAS descriptions given repeatedly by Boeing and other technical sites on the web. These MCAS descriptions are echoed in the the KNKT final report on JT610 which also contains the NTSB System Safety and Certification Specialist’s Report in Appendix 6.2 (pg. 245).
I would like to address some of these misconceptions as best I can.
Misconception 1: The 737 MAX is longitudinally (pitch) unstable
The corollary to this is is that the MAX might be stable at lower AoA’s but becomes unstable above some non-zero positive AoA. To be clear, I am talking about longitudinal static stability which is another way of saying natural pitch stability. This is different from longitudinal dynamic stability where rotational inertia, rates, and accelerations must be considered.
If the MAX was truly unstable in pitch then the control column would be very “touchy” in pitch at all AoA’s, not just large AoA’s, and in both directions, not just in the ANU direction. This would render the aircraft virtually uncontrollable by all but the best pilots. Also, a feature like MCAS can never stabilize a statically unstable aircraft. This is because the MCAS is an open loop control law (note 32 at the bottom of KNKT pg.247) and it acts through the stabilizer incidence angle.
Static stability depends on the slope of the pitching moment vs. AoA curve as Bjorn has stated several times in his Corner’s. This slope can never be changed by varying the stabilizer incidence angle or even the elevator angle. The slope is affected by the static margin, the tail length, the stabilizer area, etc, but not by the stabilizer incidence or elevator angles. Changing these angles only changes the trim AoA, i.e. slides the pitching moment curve up and down. Since the slope is not changed the static stability is not changed. This applies to all AoA’s, even if the aircraft is stalling. For an unstable aircraft, the column will be very touchy whether MCAS is active or not.
Since the NTSB stated outright that MCAS is an open loop control law, MCAS cannot be used to give the MAX artificial pitch stability, like the control systems on modern fighter jets can. Besides, the jackscrew on the 737 stabilizer is much too slow for that.
Finally, to my knowledge, I have not heard any reports that the MAX pitch control is overly touchy, nor have I heard of any reported incidences of severe MAX pitch control problems outside of the flights and crashes when MCAS misfired due to faulty/damaged AoA vanes. Because of all this, the MAX is statically stable in pitch over all AoA’s short of stall.
Misconception 2: MCAS activates at lower AoA’s that are encountered during normal flight
The fact that the MCAS activation schedule is not publicly known and Boeing has not disclosed it in detail does not mean that MCAS activates at lower AoA’s than Boeing implied in its public statements (AoA’s closer to stall).
Since Boeing hasn’t publicly revealed the AoA’s where MCAS is active, instead of appealing to the unknown to prove my point I’m instead going make an educated estimate about the AoA’s where MCAS cannot be active. Bjorn states in Part 3 of his Pitch Stability series that normal flight of a clean aircraft (no slats or flaps) is flown at 2° – 4° AoA at cruise and 6° – 8° AoA in a turn or when waiting for landing at moderate speed in a circling pattern. I firmly believe in his numbers here because he calculates these types of parameters regularly when using his aircraft performance model to evaluate various aircraft for paying customers of LNA.
For cruise and long duration turns like circling patterns, the pilot would undoubtedly trim the aircraft for those situations. When the aircraft is trimmed, any MCAS action under these conditions would appear as un-commanded AND trims any pilot would immediately notice. So, why are there no reports surfacing about the MAX suffering unexplained repetitive AND trim events happening about 5 seconds apart during normal flight, other than the flights where MCAS misfired due to erroneous AoA readings? After all, it has been a year since the first accident and many people have come forward since then, whether anonymously or not, to share/leak their information about the MAX MCAS development and certification. It is because MCAS does not activate at AoA’s that are encountered during normal flight, which is up to 8°. This is my educated estimate. My guess would be that MCAS doesn’t activate at AoA’s below 10° accounting for AoA’s that are on the high end of what is considered normal flight. The NYT article published June 1, 2019 supports this. “But a few weeks later, Mr. Wilson and his co-pilot began noticing that something was off, according to a person with direct knowledge of the flights. The Max wasn’t handling well when nearing stalls at low speeds.“
Misconception 3: MCAS is a stall protection system or an anti-stall device
Several LNA commenters have repeatedly claimed Boeing stated MCAS was an anti-stall device or stall protection system. After much searching, I can’t attribute either of these labels to Boeing. These labels for MCAS were repeated in many news stories, but quite frankly, I don’t consider news stories credible sources for the technical analysis required to come to these conclusions. As far as I’ve read, Boeing does not say this, the KNKT final report on JT610 does not say this, and the NTSB System Safety and Certification Specialist’s Report does not say this. The JATR does not state this, but only says that “the JATR team was unable to completely rule out the possibility that these augmentation systems function as a stall protection system”
My contention is that MCAS is intended to be a stability augmentation function that also happens to aid in stall recovery. This is not the same as a stall protection system or anti-stall device. Pilots can still fly MAX into a stall if they so desire.
Misconception 4: The 737 MAX has an atypical pitching moment vs. AoA curve
I can find no credible basis to support this notion.
As far as I can tell the logic to support this misconception goes something like this:
1) The Leap engines are larger and placed higher and farther forward relative to the wing on the MAX vs. the NG.
2) This engine placement causes some mysterious aerodynamic effects to occur that Boeing can not or will not explain, and experts like Bjorn Fehrm also can not explain.
3) These mysterious aerodynamic effects result a pitch up moment for the 737 MAX that is disproportionately larger than any other previous commercial twin jet
4) These mystery effects and lousy pitch up tendencies only happen on the MAX, and not on any other commercial twin jet
5) Boeing had to hide these nasty tendencies from everyone so they increased the power of MCAS hoping no one would catch on
5) The fact that MCAS has these “stealth” purposes proves Boeing must be hiding something awful
6) Because Boeing is hiding something awful, it must mean that the 737 pitching moment vs. AoA curve has to be the weirdest and most atypical one ever seen
This is supported by cultish statements of faith that highlight how atypical the MAX pitching moment curve must be, especially compared to the Airbus gold standard:
In aerodynamic reality, relative changes in effect scale reasonably with relative changes in configuration, not an order of magnitude more. This is very true at lower speeds where compressibility effects are relatively small. At higher subsonic Mach numbers, the relative changes in effect are larger but again, not an order of magnitude larger. The diagrams overlaying the NG with the MAX illustrate that the configuration changes are relatively small.
Misconception 5: Boeing designed MCAS to be a primary flight control system
The unintended authority of original MCAS resulted from how the original software handled the reset after the MCAS activated and the AoA still read above the threshold. Boeing never tested AoA sensor failure because according to their flawed safety analysis, they didn’t need to. Some LNA commenters are trying to glean way too much from how the obviously flawed original MCAS responded to erroneous AoA readings.
Excellent post – thanks. Your description of the magical thinking on many LN threads in M.4 is particularly on-point.
Suggest you save this for re-posting in a more current discussion 😉
Thank you for the kind words. I’m glad you made it to the end. It’s a bit long and I have a tendency to drone on, so I wonder if many have the patience to get all the way through.
I created it on WordPress so I do have it saved.
We did get through it, and thank you for addressing these issues by rational explanation. Very helpful to the understanding of this discussion.
Muilenburg will have the patience once he is behind bars,
good You saved it for him,
otherwise he would only have some beans to count.