Moon of Alabama Brecht quote
March 17, 2019

Flawed Safety Analysis, Failed Oversight - Why Two 737 MAX Planes Crashed

Two accidents of the Boeing 737 MAX aircraft led to a loss of 338 lives. Planes of that type are now grounded world wide. We earlier explained in detail why the incidents happened. New reports confirm that take.

For commercial reasons Boeing wanted the new 737 version to handle like the old ones. But changes in the new version required an additional system to handle certain flight situations. The development of that system and the safety analysis of its implications were rushed through. Pilots were not informed of it and not trained to counter its failure.

Boeing now hopes that a software update, planned for April, will allow its grounded 737 MAX airplanes back to the flight line. For several reasons that is unlikely to happen.

On Thursday Captain C.B. Sully Sullenberger, who successfully landed a plane on the Hudson river after a bird strike disabled both engines, spoke out against Boeing's patch up attempt:

It has been obvious since the Lion Air crash that a redesign of the 737 MAX 8 has been urgently needed, yet has still not been done, and the announced proposed fixes do not go far enough.

The public will not trust Boeing's, or the Federal Aviation Administration's assurances if Sullenberger sticks to his view.

Another reason that Boeing's update will not suffice is a detailed bombshell report researched mostly before last Sunday's crash but just now published by the Seattle Times. It summarizes:

[T]he original safety analysis that Boeing delivered to the FAA for a new flight control system on the MAX — a report used to certify the plane as safe to fly — had several crucial flaws.
...
Current and former engineers directly involved with the evaluations or familiar with the document shared details of Boeing’s “System Safety Analysis” of MCAS, which The Seattle Times confirmed.

The safety analysis:

  • Understated the power of the new flight control system, which was designed to swivel the horizontal tail to push the nose of the plane down to avert a stall. When the planes later entered service, MCAS was capable of moving the tail more than four times farther than was stated in the initial safety analysis document.
  • Failed to account for how the system could reset itself each time a pilot responded, thereby missing the potential impact of the system repeatedly pushing the airplane’s nose downward.
  • Assessed a failure of the system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.

The 737 MAX maneuver characteristics augmentation system (MCAS) depends on the input of a vane on the side of the airplane.


Angle-of-attack sensor

The vane measure the angle between the airflow and the wing. It thereby detects if the nose of airplane points up or down. It can easily be damaged by a ramp accident or due to a bird strike. The MCAS system depends on the input of only one of these sensors.

The corrections MCAS applies to the trim of the airplane are too large for a busy pilot to counter. (A detailed explanation of the system and the accidents is provided by a professional pilot in two videos here and here.) That the system, as designed, engages repeatedly can lead to situations that are extremely difficult to handle.

The Seattle Times also reports that managers at the FAA pushed their safety engineers to delegate more certification tasks to Boeing itself. Boeing was eager to get the new version of the 737 out of the door to catch up with Airbus's A-320 NEO. Shortcuts were taken to rush the safety analysis through.

The MCAS system is poorly engineered and the design should never have been certified in the first place. But the issue is even worse. The certification that was given relied on false data.

The first MCAS design, on which the safety analysis and certification was based, allowed for a maximum trim movement by MCAS of 0.6 degree of a maximum of 5 degree. Flight tests proved that to be too little to achieve the desired effects and the maximum movement was changed to 2.5 degree. A safety analysis for the new value was not conducted.

“The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
...
“None of the engineers were aware of a higher limit,” said a second current FAA engineer.

Boeing and the U.S. government have a special relation. All administrations, independent of which party rules, give it extraordinary support. That leads to regulatory capture. The FAA is under constant political pressure to relent to Boeing's demands:

For Boeing’s 102-year history, dating to the start of the First World War, the company and the country have relied upon one another, together creating hundreds of thousands of jobs, outfitting the United States with top military aircraft and supplying planes worldwide to allow the growth of passenger air travel and to boost U.S. exports.
...
“Whenever the government is seeking to enhance exports, usually you’re going to find that Boeing is heavily involved in whatever initiative they’re carrying out,” said Andrew Hunter, a defense industry expert with the Center for Strategic and International Studies. “That was true in the Obama administration, and it’s true in the Trump administration.”
...
“The risk is obviously that when agencies that are regulatory in nature work closely with a company over a long period of time, the concern is that it could undermine its independence,” Hunter said.

After the accident last Sunday Boeing used its political connections to prevent the grounding of the 737 MAX. Only after all other countries prohibited further flights did the U.S. join in. It was the president, not the FAA, who announced the decision.

The new reports about the outsourcing of FAA safety analyses to Boeing itself, and of the inappropriate certification process, add to the impression that the FAA can no longer be trusted. Even if it certifies Boeing's patch-up solution for the MCAS problem other regulators will disagree.

That then will become a severe political problem. Trump's trade negotiations with China depend on the Chinese willingness to buy a large number of Boeing planes. If the Chinese regulators, who were the first to ground the MAX, do not accept the solution Boeing provides, those trade negotiations will go nowhere.

It is clear than that Boeing will have to provide a better solution. The U.S. government will have to strengthen its aviation regulator and will have to protect it from political pressure. Should either not happen Boeing's role in the international airline business will be severely damaged.

Posted by b on March 17, 2019 at 12:26 PM | Permalink

Comments
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@ Jen # 101 with the link about safety options for the 737 Max

Of course the lawyers always win, but it will be interesting to see how this plays into the legal mess that this will become. Are the airlines on the hook or should have Boeing provided it w/o it being an option for more money?

Why does the West allow profit between consumers and risk management decisions they are not made aware of?

I also want to state that I doubt that the rest of the airplane manufacture's are perfect with regards to their cost/risk management decisions. Because of PROFIT all are forced to operate within a lower safety priority in risk management decisions.

We have a systemic problem that only gets solved by getting rid of the PROFIT motive and that motive/narrative is brought to you by global private finance of centuries reign.

Posted by: psychohistorian | Mar 18, 2019 9:53:56 PM | 101

I did some web surfing about fatal airplane crashes, and the realm of small short-haul airplanes is definitely quite lethal, although it faces a myriad of risks that the "jet set" will probably never face. E.g.

25 August 2010. A Filair L-410UVP-E20C crashed with 20 fatalities in Bandundu, Democratic Republic of the Congo. According to the sole survivor, the crash was caused by a stampede of passengers after a crocodile escaped from a bag in the cabin. The crocodile itself survived the crash, but was killed by rescuers.

Posted by: Piotr Berman | Mar 18, 2019 10:31:12 PM | 102

Piotr Berman@103 - That crash was clearly pilot error. He should have followed Filair's in-flight emergency checklist for sudden, unexplained appearance of unconstrained alligators, crockodiles and eusuchians. The rear cargo door of the aircraft is opened, no smoking light illuminates, set flaps 15, engines to 80% nose trimmed up 12. When the giant lizards have slid back to the rear galley area, then violently rocking the aircraft back and forth will usually be successful in deplaing one or more of them. Thying to get them so sing show tunes will callm them down. They're quite good at it. Otherwise, they're likely to be scared of all the commotion. Sometimes they manage to snag a seat or some luggage with them out of anger as they fly out the door. That can be sorted out once the aircraft is safely back on the ground and tertieved.

And despite what one might think about the result of a high-altitude drop, those things are remarkable armored and surprisingly durable. They'll roll once or twice after a tremndous impact, get up and make a bit of an angry screetching sound. Then they just walk away like it never happened.

Posted by: PavewayIV | Mar 19, 2019 12:40:11 AM | 103

@103 Let me guess: the sole survivor went by the name of David Dunn.

And all the black box recorded was Elijah Price (in a wheelchair, naturally) shouting "Enough is ENOUGH! I have had it with these motherf**kin' alligators on this motherf**kin' plane!"

Posted by: Yeah, Right | Mar 19, 2019 5:28:38 AM | 104

> Boeing offering the two safety options for sale? Neither the Lion Air jet nor the Ethiopian Airlines jet had these safety options.

Posted by: Jen | Mar 18, 2019 9:37:45 PM | 101

This claim is half-true.
There was no two option but a one single option: informing pilots when AoA sensors disagree (showing at least one or maybe both sensors failed).

The claim that Boeing 737 had only single "no redundancy" AoA sensor is wrong - they have two sensors, always.

MCAS however, being last time "ugly patch" ignored that redundancy, it just kind of randomly picked one sensor and only used it for the flight. This time it picked wrong sensors.

Posted by: Arioch | Mar 19, 2019 7:09:18 AM | 105

There seems to be something very American in *selling* emergency information as deluxe option.

Airbus informed pilots dozen years ago in Quantas case - and ground team then instructed pilots how to regain control.

Also, if someone did not hear about Three Miles Island nuclear accident - one better read it.
That nuclear accident was made possible by the same idea: selling situational awareness as extra deluxe option.
When different crew members failed to understand one another and pushed nuclear reactor into self-destructing mode - NPP did not informed them until melting started.

Posted by: Arioch | Mar 19, 2019 7:12:43 AM | 106

Paveway IV: your confused advise for the crew shows that the problem is not easy to address, but since no similar accident repeated in the Democratic Republic of Congo, one may guess that proper measures were taken. E.g. while screening luggage, do not put your hand inside a bag without some prior checking of the content, but if you loose your palm in spite of precautions, do not allow the bag on the plane.

Posted by: Piotr Berman | Mar 19, 2019 7:43:43 AM | 107

This claim is half-true.
There was no two option but a one single option: informing pilots when AoA sensors disagree (showing at least one or maybe both sensors failed).
The claim that Boeing 737 had only single "no redundancy" AoA sensor is wrong - they have two sensors, always.
MCAS however, being last time "ugly patch" ignored that redundancy, it just kind of randomly picked one sensor and only used it for the flight. This time it picked wrong sensors.
Posted by: Arioch | Mar 19, 2019 7:09:18 AM | 106

The statement in bold applies to Arioch's confused proposition at least as much as to Jen's, if not more so.

There are two AoA sensors on ALL 737Max aircraft, one on the left and one on the right. Each of the sensors is connected to a flight control computer: the left sensor is connected to the flight control computer on the left hand side of the aircraft, while the right sensor is connected to the flight control computer on the right hand side of the aircraft. However only one of the two sensors is used at any given time because the aircraft uses only one of the two flight control computers, alternating between successive flights.

Normally there is no connection between the two sensors, and the sensors can only be accessed through the relevant flight control computer, but Boeing offers an option - for US$60,000 (sounds like a true Mafia option, doesn't it?) - to install a warning signal that indicates when the two sensors are in disagreement. Neither of the two 737Max's that crashed had the option installed.

There is NO redundancy in the two AoA sensors, unless the option is purchased. If the option is not purchased, there are two sensors in existence on the aircraft but the flight control computer only uses the signal from one of them, so no redundancy is in effect.

Posted by: BM | Mar 19, 2019 9:50:32 AM | 108

FAA is no longer trusted. Lots of court cases, including criminal ones, are coming up:

Canada re-examining Boeing 737 MAX approval after FAA certification probe

Transport Canada is re-examining the validation it gave Boeing Co’s 737 MAX jets, following reports of a U.S. probe into the aircraft’s certification by the Federal Aviation Administration (FAA), Canada’s transport minister said on Monday.
...
Garneau added that Transport Canada would do its own certification of a software change being prepared by Boeing within the next few weeks “even if it’s certified by the FAA.”
...
Citing people familiar with the inquiry, the Wall Street Journal reported on Sunday that U.S. Department of Transportation officials were scrutinizing the FAA approval of MAX jets and that a grand jury in Washington subpoenaed at least one person involved in developing the MAX.

In addition, the Seattle Times reported that Boeing’s safety analysis of a new flight control system on MAX jets, known as MCAS, had several crucial flaws, including understating the power of the system.

When Bombardier in Canada developed a competitor plane for the 737 MAX-7 Boeing alleged price dumping and Washington intervened on Boeing's behalf by putting a 200% duty on it. Bombardier was under financial pressure. Airbus aquirred a majority of it and now sells the plane as A-220.

Now its payback time for Canada. Other regulators will follow its step.

The Russian MC-21 development, also in the same class as the 737, was blocked by U.S. sanctions on two Russian companies who made the composite wing for those planes. Composite sales to Russia were prohibited and the plane thereby delayed by two years. Russia is now making the composites itself and MC-21 deliveries will start in 2020.

The Chinese were even more clever. Their new C919, also in the 737 class, is large build by joint ventures with U.S. companies. Sanctions on it would cost U.S. jobs. That gives it some lobby support in DC.

Two days ago the Ethiopian ambassador to China visited an air show and tweeted pictures of himself sitting in a C919 cockpit.

A not so subtle hint that the 737 MAX era in Ethiopia Airline is coming to a rapid end.

The 737 cash cow will no longer be such for Boeing.

Posted by: b | Mar 19, 2019 10:19:35 AM | 109

The two Boeing crashes have turned a spotlight on that company, and also towards the FAA. Events which might have remained in the shadows are now visible. Link via the xymphora site:

Two 737 MAXs have fatally crashed. The new model may not have enough space to evacuate passengers in time.

Posted by: Zachary Smith | Mar 19, 2019 11:31:58 AM | 110

Hyper-Hypocrisy of The West about ISIS

Something about the author rubs me the wrong way, but I can see nothing in this piece as obviously wrong. And other sources I've read agree with much of what he presents here. Is the US really trying to move ISIS to Sweden so it will be "available for future combat"? ISIS came within a hair of destroying Iraq (again) and also almost smashed Syria. Who would be the next target? The Muslim areas of Russia or China?

Posted by: Zachary Smith | Mar 19, 2019 11:44:52 AM | 111

There is NO redundancy in the two AoA sensors

> Posted by: BM | Mar 19, 2019 9:50:32 AM | 109

This is akin to fierce argument about "where is that there".

For me "There" means the aircraft, because that is the SKU, thee unit built and sold by Boeing
The aircraft DOES have two sensors measuring independently the same aspect of reality.
That IS the redundancy - two independent unit doing the same work.

The fact that the rest of the aircraft typically and that MCAS always discard this redundancy in favour of ignorant simplicity - does not mean redundancy is absent. It means it is present, but discarded, instead of used.

However if ones would cherry-picks any other definition of what "there" means in context of Ethiopian Airline disaster, then he can come to any desired conclusion w.r.t. presence of redundancy in presence of two independent sensors measuring the same thing.

Posted by: Arioch | Mar 19, 2019 12:04:55 PM | 112

B> Boeing alleged price dumping and Washington intervened on Boeing's behalf by putting a 200% duty on it. Bombardier was under financial pressure. Airbus aquirred a majority of it and now sells the plane as A-220.

Wikipedia> Airbus plans to open a second assembly line for the aircraft at its Mobile, Alabama factory

O-oh... :-D

Posted by: Arioch | Mar 19, 2019 12:11:15 PM | 113

@JOshV #44
The VW issue wasn't design flaws - it was deliberate design to pass emissions testing.
As for size: hard to say.
VW's liability is in the millions of diesel cars sold and the resulting loss in value.
Boeing losses will come from not just the hardware itself, but the many thousands tens of thousands or or even hundreds of thousands of flights not flown by the airlines that bought the 737MAX. If we assume say, 150 seats average with 75% capacity ratios, with each sold seat = $200, we're looking at $22500 max potential losses per flight. 10K flights = $22.5M.
Possible numbers? 350 737 MAX planes have been sold as of January 2019, according to wikipedia. Commercial flights probably average about 6 per day.
350*6 = $47.25M per day
Actual numbers are certainly lower: the passenger fares include fuel and non-hardware operating costs while not all 350 planes sold are probably actually flying, but the above gives a rough idea of how much the liability could be.
30 days = $1.4B in potential airline losses.

Posted by: c1ue | Mar 19, 2019 1:34:55 PM | 114

Also Europe will run its own tests.
"The European Aviation Safety Agency (EASA) will keep Boeing’s 737 MAX 8 grounded until it performs its own safety tests on the jet. In the US, the Federal Aviation Administration (FAA) faces scrutiny for certifying the plane"
https://www.rt.com/news/454229-european-air-regulator-doesnt-trust-faa/

Posted by: Peter AU 1 | Mar 19, 2019 1:40:47 PM | 115

Assessed a failure of the system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.
(from this article we're commenting on)

That IS the redundancy - two independent unit doing the same work.

Quit trolling Arioch, you should know better by now.

Posted by: Vasco da Gama | Mar 19, 2019 2:05:46 PM | 116

Posted by: mourning dove | Mar 17, 2019 1:50:07 PM | 10

"Excellent b, thank you.

Wonder where the troll "pilots" are now lol."

Troll pilot reporting for duty.

Sorry about being awol, but I've got better things to do with my life(even at this late stage) than to go to websites, where I'm not welcome, to stir up trouble. Today is the first day that I've been back here since I last commented, on the earlier MCAS board.

I'm not an "enemy" of b and MoA, in fact I really like both, that's why I've been coming here frequently since I discovered this hangout a year ago, during the Skripal case. I got here from a link posted on The Blog Mire I think. I agreed with TBM on the Skripals(roughly that the UK government, in general, and Mad May in particular was telling nothing but lies. I'm still of that opinion(see also Craig Murray for good stuff on that).

I'f somebody tells you that you are wrong, in a non-abusive way, about something, she is your friend not enemy. Friends help to correct errors, enemies let you make them.

I shall now go back to the start of the board and correct a few errors. I'm sure that I will only be able to manage a few as I'm not willing to spend much time at present.

If b would like to contact me directly please email me. I specifically authorise you to do so on the email under which I post.

Posted by: acementhead | Mar 19, 2019 6:37:09 PM | 117

Posted by: Kupkee | Mar 17, 2019 1:01:13 PM | 3

"Also, how hard is it to place an over-ride to get the MCAS out of the picture during take-off?"


Kupee the MCAS IS "out of the picture" during take-off. It is active(ie watching for any occurence of AoA greater than the AoA for which it is set. I do not know what that is but likely quite high >12 degrees?) only when

1) the flaps are retracted
and
2) the autopilot is disengaged.

It is completely disabled(all electrically commanded trim is) when the stab trim override switch is set to cutoff. This switch(was only one of them on the early models of B737 that I flew, could be a pair on the 800, don't know but it is irrelevant to the discussion) is less than a metre from the captains right hand, when on the control wheel, located on the rear of the pedestal and isolated from other switches. You can move it, without looking, to cutout with 100% certainty.

Posted by: acementhead | Mar 19, 2019 6:57:55 PM | 118

Posted by: joaopft | Mar 17, 2019 2:56:58 PM | 13

"The MCAS is there to prevent stalls caused by a large angle of attack (AOA) to become unrecoverable. Unlike the 737 NG, the 737 Max 8 (with MCAS turned off) will naturally pitch up, instead of down, when it stalls due to high AOA.

This is due to the fact that, despite the advertising, the aerodynamic characteristics of the Max are quite different from the NG. The large nacelles at the front of the wings provide lift at high speeds, performing like (unintended) canards. As they are placed forward the centre of mass, they add a pitch up moment. These "canards" are poorly designed, in the aerodynamic sense, because they should stall at a lower AOA than the wings. If that were so, the plane would tend to pitch down right before the stall (instead of up), making the stall more easily recoverable. The MCAS has been put there to fake the stable flight recovery characteristics of the 737 NG, that the MAX does not naturally enjoy."

Excellent comment from joaopft. He is the first commenter that I've seen here apart from myself, Steven and maybe the Russian guy(I found his comments hard to read and didn't really try too much), who knows what he is talking about.

It is posssible that there are others getting things right, haven't got there yet.

Posted by: acementhead | Mar 19, 2019 7:17:22 PM | 119

Has anyone else posted today's piece at Naked Capitalism? I've found this to be a complicated issue, and this author provided the best summary I've yet seen.

Boeing Crapfication: 737 MAX Play-by-Play, Regulatory Capture, and When Will CEO Muilenburg Become the Sacrificial Victim?

"Self Certification" is a very bad idea, and that's what we have now in way too many areas. Some intelligent hardware/software tinkering may well fix things in this case, but my trust in both Boeing and the FAA will probably remain at the snake-belly level.

Posted by: Zachary Smith | Mar 19, 2019 7:25:35 PM | 120

Posted by: Jen | Mar 17, 2019 5:25:29 PM | 29


"The pilots can deactivate the MCAS only if they know it is there in the first place."

That is not true. If, FOR ANY REASON, not just faulty MCAS, there is unwanted stab trim movement, in either direction not just forward as MCAS does, the pilot can and should immediately disable electrical trim. This is accomplished in half a second.

Whenever the stab trim moves the BIG wheels on EACH side of the pedestal move. Impossible to miss if the pilot is awake.

Posted by: acementhead | Mar 19, 2019 8:02:32 PM | 121

Not a pilot but my understanding from the aviation forms is this.

MCAS activation does not resemble runaway trim so the cut off switches will not be shut off immediately , at least not before attempting to control by pulling back on the yoke and then manually via switches on the control column. However, every time the pilots reset the switches on their control columns to pull the nose back up, MCAS would have kicked in again and “allowed new increments of 2.5 degrees.”
“So once they pushed a couple of times, they were at full stop,” meaning at the full extent of the tail swivel (up to 20 deg ) which would be difficult to reverse manually after cutting off electricity to the trim, due to large forces to turn the trim wheel and large number of wheel turns required.

There was also a time component also as the problems occurred at low altitude and only a matter of minutes to deal with a situation that has not been properly dealt with in the operating manual or in simulators, with the stick shaker shaking and alarms of an imminent stall due to a faulty sensor

So yeah, on take off on this craft a properly trained pilot on takeoff deactivates the MCAS and assumes a faulty sensor when MCAS takes control, or perhaps gets a warning one of the AoA sensors is faulty, something that Boeing should have provided as standard

Posted by: Pft | Mar 19, 2019 10:16:44 PM | 122

acementhead - Regarding the FDR data on Lion Air JT610 [link]

Any reason the pilot would redeploy flaps after the initial MCAS activiation? 300 kts. seems way to fast do that - wouldn't the robot keep them from really being deployed? I understand the excessive speed and apparent loss of lift might be (theoretically) countered by flaps/slats, but are they ever used like that on a big jet?

Also concerning V(a) - Maneuving Speed for the -800 is 260 kias at sea level. Near the end of the recording, the pilots were both fighting the stab trim with the elevator as the speed climbed to 300kts. What is going to break first if it breaks - the elevators or the whole stabilzer?

Posted by: PavewayIV | Mar 19, 2019 10:31:07 PM | 123

On March 12 b posted, in the head post labeled

Boeing, The FAA, And Why Two 737 MAX Planes Crashed

inter alia

"The MCAS engaged and put the planes nose down. The pilots reacted by disabling the autopilot and pulling the control stick back. The MCAS engaged again pitching the plane further down. The pilots again pulled the stick. This happened some 12 times in a row before the plane crashed into the sea."

This is incorrect IF, and that is extremly likely, the only defect was faulty MCAS(for whatever reason). That is because the MCAS is NOT 'on watch', ie monitoring, if the auto pilot is engaged. It puts in nose down trim(if the condition calling for it occurs, ie the threshold excess AoA is met) when auto pilot is not engaged and NOT when the autopilot is engaged.

If the pilots had been worth a damn they would have disarmed the electrical trim in half a second or so when any undesired trim was taking place. There would have been no need to be that quick but easy to do so.

From b again

"They were not aware of an automatic system that controlled the stabilizer even when the autopilot was off. They had no idea how it could be deactivated."

They should know exactly how to "deactivate it.

They did not need to know about MCAS to know what to do. The action is always the same no matter what the casue.
Runaway stabtrim has a single, quick, easy fix. Runaway is whenever there is an undesired stabtrim movement. It is EXTREMLY rare. The vast majority of airline pilots go their whole career and never experience it or even hear of it happening to a fellow pilot. Nevertheless the action in the event is easy, and quick. It is one of the few "memory" items in B737 abnormal procedures. The cause of the runaway is irrelevant, the action is the same.

During airline operation by competent pilots an airliner never gets near to the AoA at which MCAS puts in trim. Again no competent pilot will ever see MCAS do anything.

Posted by: acementhead | Mar 20, 2019 1:30:17 AM | 124

PavewayIV | Mar 19, 2019 10:31:07 PM | 124

wrote

"Any reason the pilot would redeploy flaps after the initial MCAS activiation? 300 kts. seems way to fast do that -"

There is absolutely no reason to redeploy flaps. 300 kts is way above speed for flaps 1 degree(on Boeing flaps positions are denominated in degrees as compared to airbus in which flap setting positions are just numbered 1, 2, 3, etc). Even at 300 knots the trailing edge flaps would likely not be damaged; they have started to extend but mainly just running "out" not down. 1 degree is still basicaly fared. The leading edges though would likely be well over-stressed. Remember that aerodynamic loads such as on the leading adge flaps are proportional to the square of the speed. I have not flown the 800 but earlier models that I flew(40 years ago) flap 1 maximum speed was 232 KIAS(knots indicated airspeed)

"... wouldn't the robot keep them from really being deployed?"

On the models that I flew (200, 300) there was no automated speed inhibion of flaps. Back then pilots were expected to be able to fly: and we could. If the Lion air pilots redeployed flaps at or near 300KIAS then there is clearly no speed inhibition of flaps on the 800; nor should there be in my opinion. Pilots should be able to fly.

"I understand the excessive speed and apparent loss of lift might be (theoretically) countered by flaps/slats, but are they ever used like that on a big jet?"

There was no "loss of lift", just failure to control in the pitch plane. Are they ever used like that, in big jets; no nor even in small ones.


"Also concerning V(a) - Maneuving Speed for the -800 is 260 kias at sea level. Near the end of the recording, the pilots were both fighting the stab trim with the elevator as the speed climbed to 300kts. What is going to break first if it breaks - the elevators or the whole stabilzer?"

Maneuvering Speed in the maximum speed at which full aileron my be applied. Nobody ever uses full aileron in normal airline flight. The only time Ive ever used full aileron is during aerobatics in light aircraft. Roll control was not an issue here, the problem was pich and speed control. Speed got way too high because the pilots were idiots and did not reduce thrust.

At 300 knots I don't think either elevator or horizontal stabiliser would be damaged no matter how mistrimmed the aircraft was, however I have no data on the matter.

Posted by: acementhead | Mar 20, 2019 2:11:43 AM | 125

PavewayIV 124

From what I have seen on the commercial aircraft pilots forums, both planes were doing about the same speed before they disappeared off radar. Pilots thinking they were stalling, or using speed to try and gain lift at low angle of attack .. I don't think so. Both cases are very similar as they both took the first dive at around flaps up altitude. MCAS may be hooked into more than just the HS.
Also stick pressure. I realize that like bid macs have artificial color flavour and scent, Boeing controls have artificial feel fed in the system. Any idea of the pressure required to get full back stick at those sort of speeds. One pilot or two to get maximum elevator deflection for nose up.
MCAS was designed to over-ride manual operation to prevent catastrophic stall. Makes me wonder if it is not also hooked into auto throttle and feel (control forces). Most auto systems are designed to make life easier for the pilot and passengers, but MCAS is designed to over-ride pilots.
The other thing that I have picked up on the CP forums is that in both cases, the pilots were using manual electric trim to get the nose up. Why would they stop using manual electric to get the nose up and dive into the ground instead. MCAS, I think, is more deeply wired into the aircraft than Boeing or FAA are currently letting on.

Posted by: Peter AU 1 | Mar 20, 2019 2:19:38 AM | 126

"I realize that like bid macs"... should have been big macs

Posted by: Peter AU 1 | Mar 20, 2019 2:27:15 AM | 127

meat head

You are here to pump for boeing, but I did run onto a few or your type when learning to fly. Most of these were from general aviation, and apart from following the rules and having full faith in the powers that be, did not know the difference between a shit sandwich and a snag in a bread roll.

Posted by: Peter AU 1 | Mar 20, 2019 3:22:11 AM | 128

I don't know much specifically about aircraft systems, but I do know that in all corporate sectors there's a powerful trend to put machines in charge as much as possible, override human initiative and decision making as the "default setting", and if possible eliminate humans completely from the process. This is driven both by engineering theology and by regular capitalist "labor-saving" i.e. job-destroying program. The same mentality which wants to force automated factories and self-driving cars upon the world would fantasize doing the same with self-flying planes.

Therefore it's highly plausible that the MCAS is designed to override pilot decision and require some kind of convoluted action to wrest control of the plane from it. As for the mentality we've been seeing which has such contempt for "shit pilots" and automatically wants to blame the pilot, that simply parrots the mentality of the technocrats at Boeing and the FAA, who despise all pilots as an unwanted but necessary human component screwing up their otherwise perfect techno-process. Same for whiny passengers who don't want to crash, who want air travel to be comfortable etc.

As for crashing, I know from many years of writing about poison-based agriculture, an ongoing failure and disaster even according to its own premises, that engineers and bureaucrats (including the top executives and officials and big shareholders - they're still essentially bureaucrats) don't care if their products actually work, they only worship the idea of the technology, and of course the money and power they can force with it.

Posted by: Russ | Mar 20, 2019 5:50:34 AM | 129

acementhead@126 - Thanks for the detailed reply. The pilots seemed baffled by speed and altitude readings, but re-deploying flaps seemed odd. Did the older (pre-NG) models also have the single-sided stick shaker? That seems like an odd design choice to me. How does the F/O know the captain's stick shaker has activated?

Peter AU 1@127

"... Any idea of the pressure required to get full back stick at those sort of speeds..."

If the units are in pounds (could be newtons, kilos, some other unit) the Lion Air FDR graph shows nearly 80 lbs. of applied stick pressure (pulling the wheel back) by the F/O, then 100 lbs. applied by the pilot. This was the last 30 seconds of the flight. Both hands would be needed for that kind of pull, meaning no free hand to switch anything.

"...Why would they stop using manual electric to get the nose up and dive into the ground instead..."

From an NG flight controls pdf [link]:

Trim authority (limits):

Manual (wheel) trim -0.2 to 16.9 units
Electric (switch) trim flaps extended -.05 to 14.5 units
Electric (switch) trim flaps retracted 3.95 - 14.5 units [737-800]

That means you can't use electric trim to push the nose down any more than 3.95. I haven't seen a description if you can use electric trim to push the nose up if you're already below 3.95 (I would guess 'yes')

There's yet another 'layer' protection with the column cutout switches. If you move the stick far enough back in opposition to the nose-down trim - which happened in JT610 - the electric and/or autopilot trim is disabled. Logically, that would only disable more nose-down electric trim considering you were already pulling back on the stick. Column position doesn't affect MCAS, which would continue to trim nose-down. If the column cutout switches disable ANY electric trim, then they may not have been able to get the trim back up by what had worked before: using the electric trim switches on the wheel. There is a way to tell the robot to ignore column position and NOT disable electric trim - it's the STAB TRIM OVERRIDE switch on the center console.

Satcom Guru had a simplified block diagram of the signal path, but it doesn't distinguish between UP and DOWN electric trim signals (if there is any). []

https://www.satcom.guru/2018/11/stabilizer-trim.html

We don't know if the pilots stopped trying to trim the nose up, or if they couldn't for some reason. I have to go with the previous comments that (at least for JT610) the pilots should have figured out a trim robot was trying to kill them and turned it off - regardless of why (MCAS) the trim robot was so enthusiastic about doing that. I'm not blaming them, just saying it's strange they never seem to have bothered. Then again, maybe they did - I wonder how much of the legacy 'electrical cutout' (= physical electrical disconnect) really applies. If it's just another signal to the flight control computer, then it might have been ignored. IDK...

Posted by: PavewayIV | Mar 20, 2019 2:40:21 PM | 130


“It is not physically possible to wind the trim wheel that fast for that long manually, especially when your aircraft is lurching about like a rodeo bull.....

My First Point: If we don't catch this mis-trim early, un-doing it manually will take a very long time and maybe more time than is available when your aircraft is only 1000' AGL....

Second: For all the arm-chair Monday morning QB's who are saying: "Oh, they should have recognized it immediately and disconnected the trim:" (1) Just after takeoff there is a lot going on with trim, power, configuration changes, and as noted above, the darn speed trim is always moving that trim wheel in seemingly random directions to the point that experienced NG pilots would treat its movement as background noise and normal ops. Movement of the trim wheel in awkward amounts and directions would not immediately trigger a memory item response of disconnecting the servos. No way.

The pilots could very reasonably not have noticed the stab trim movement. Movement of the stab trim on the 737 is indicated by very loud clacking as the wheel rotates. ....HOWEVER, the 737 cockpit is NOISY. It's one reason I am happy to not be flying it any more. The ergonomics are ridiculous. Especially at high speeds at low altitudes. With the wind noise, they may not have heard the trim wheel moving. The only other way to know it was moving would be yoke feel and to actually look at the trim setting on the center pedestal, which requires looking down and away from the windows and the instruments in a 'leans'-inducing head move. On the 717, for example, Ms. Douglas chimes in with an audible "Stablizer Motion" warning. There is no such indication on the 737.

The fact that they were at high power and high speed tells me the stick shaker was activated. With that massive vibrator between your legs, alternating blue sky and brown out the window, your eye balls bouncing up and down in their sockets as the plane lurches up and down in positive and negative G's, it would have been a miracle if one of the pilots calmly reached down, flicked off the stab servo cutout switches, folded out the trim handle, and started grinding the wheel in the direction of normalcy.

These pilots said over the radio that they had "unreliable airspeed". So they did not even know which instruments to rest their eyes on for reliable info..... And the flying pilot may have been using the tiny standby IFDS for airspeed and attitude. Ouch.

Finally, runaway stab trim is a very, very rare occurence up until now. We trained it about once every other year in the sim because it is so rare. And when we did it was obvious. The nose was getting steadily heavier or steadily lighter with continuous movement of the trim wheel. That is a VERY different scenario than what these pilots faced....


A better question might be: given this nose down attitude, high speed, and fully nose down or almost fully nose down stab, how much altitude would they have had to have to be able to recover. I'm thinking at least 10000 feet to recognize the problem, disconnect the switches, fold out the handle and start frantically winding the stab back to normalcy while the flying pilot tries to gain control via the elevator. It's entirely possible that this scenario, if not recognized early on, is unrecoverable at any altitude.

Reference https://www.physicsforums.com/threads/boeing-737-max-mcas-system.967958/page-14

Posted by: Pft | Mar 20, 2019 10:22:32 PM | 131

PavewayIV

Zero on the horizontal stabilizer appears to be the point at which the airfoil is neutral. Neither lift nor downforce in level flight. on the tail markings, there are 2 units (I took this to be degrees) above the zero and quite a number below the zero.
The HS is an upside down airfoil with the majority of its adjustment designed to give down force at the tail. I am not sure how the scale on the tail of the aircraft correlates with the scale on the trim wheel. Looking at the markings on the trim wheel, specifically the green area for take off, two adjustments of 2.5 units by MCAS, uncorrected, would set the HS to fully nose down position (provide maximum lift at the tail).

Thanks for your links.

Posted by: Peter AU 1 | Mar 20, 2019 10:58:09 PM | 132

PavewayIV | Mar 20, 2019 2:40:21 PM | 131

"acementhead@126 - Thanks for the detailed reply. The pilots seemed baffled by speed and altitude readings, but re-deploying flaps seemed odd. Did the older (pre-NG) models also have the single-sided stick shaker? That seems like an odd design choice to me. How does the F/O know the captain's stick shaker has activated?"

Yes redeploying flaps seems very odd. Perhaps they thought that it would help raise the nose, I really can't say.

On the 737s that I flew you could feel the stickshaker on both columns. I'm fairly sure that there was a shaker unit at the bottom front of both capt and F/O control column. There was test switch located I think(almost 40 years since I flew 737) on the overhead panel. Only time I ever felt stick shaker(apart from the pre-flight test) was in Sim on approach to stall on initial conversion.

Electrical trim will operate to return back to electrical trim limit if forward of normal electrical trim authority. Can't remember the numbers.

"We don't know if the pilots stopped trying to trim the nose up, or if they couldn't for some reason. I have to go with the previous comments that (at least for JT610) the pilots should have figured out a trim robot was trying to kill them and turned it off - regardless of why (MCAS) the trim robot was so enthusiastic about doing that. I'm not blaming them, just saying it's strange they never seem to have bothered. Then again, maybe they did - I wonder how much of the legacy 'electrical cutout' (= physical electrical disconnect) really applies. If it's just another signal to the flight control computer, then it might have been ignored. IDK..." "

Last bit first. Stab trim main electrical cut-out is direct on early 737, I'm almost certain that it still is on 800. It makes no sense to do otherwise. All flight controls on 737s are hydraulically powered manually controlled, not FBW so no point in extra pointless complication. That's just not what Boeing do.


Under high-stress situations even pilots whom we might expect to perform well can sometimes do poorly in certain respects. See the BEA report on last 30 secs or so of US Airways Flight 1549.


When the aeroplane is trying to kill you the captain's job is to stop it. At all times the captain's job is to ensure safe completion of flight NO MATTER WHAT. As I put in an earlier comment, and provided a personal example, sometimes one needs to operate outside the Operations Manual or AFM even doing the opposite of what's laid down. I believe that the previous day the crew had the same problem. Flew the day, noted in engineering log and went home. No big deal. They did the correct and obvious thing and had no trouble.

Posted by: acementhead | Mar 20, 2019 10:58:30 PM | 133

Correction to my 104 above, of course it was the Lion Air aircraft which the previous day's crew had found the MCAS problem easilly solved. As they should. Did their job. No biggie.

Posted by: acementhead | Mar 20, 2019 11:40:30 PM | 134

A couple of sections from the JT610 preliminary report.

At 23:22:56 UTC, the LNI610 SIC asked the TE controller the speed as indicated on
the radar display. The TE controller responded to the LNI610 that the ground speed
of the aircraft shown on the radar display was 322 knots.

At 23:31:09 UTC, the LNI610 PIC advised the ARR controller that the altitude of the
aircraft could not be determined due to all aircraft instruments indicating different
altitudes. The pilot used the call sign of LNI650 during the communication. The
ARR controller acknowledged then stated “LNI610 no restriction”.


More happening than runaway trim. Since the preliminary report was put out, the voice recorder has been found. Australia is involved in the JT610 investigation and Australia was very close behind China in grounding these aircraft.

Posted by: Peter AU 1 | Mar 21, 2019 12:33:28 AM | 135

With JT610 the AOA sensor had also been replaced and tested one flight before the last. Seems likely the problem runs a little deeper than faulty sensors.

Posted by: Peter AU 1 | Mar 21, 2019 12:37:21 AM | 136

Flying hours in 737 for the pilots of JT610

PIC Total on type : 5,176 hours
SIC Total on type : 4,286 hours


Posted by: Peter AU 1 | Mar 21, 2019 1:28:30 AM | 137

"The corrections MCAS applies to the trim of the airplane are too large for a busy pilot to counter. (A detailed explanation of the system and the accidents is provided by a professional pilot in two videos here and here.) That the system, as designed, engages repeatedly can lead to situations that are extremely difficult to handle.'

That pilot has put a third video. https://youtu.be/9Ts_AjU89Qk?t=390 At around the 6.30 mark he talks about the difference between these incidents and how they differ from all other runaway trim incidents that pilots have trained for. Also speaks on the difference between having just two pilots and having three or more pilots.

Posted by: Peter AU 1 | Mar 21, 2019 7:35:52 AM | 138

Can anyone point me to the actual cost of the retraining which pilots would have to do without the MCAS and which Boeing was trying to avoid? I'm thinking that in practice pilots would have no problem adapting and that a mere mention of the slightly changed characteristics would be enough, but that due to strict procedures the adaptation turns into an expensive retraining procedure which then turns out to be very costly. In short, I'm playing with the idea of a gradual disconnect of reality from increasingly tight and expensive formal procedures.

Posted by: tuyzentfloot | Mar 21, 2019 8:08:52 AM | 139

A section at the 24 minute mark. According to this pilot also a qualified spanner man, MCAS is also hooked up to the throttles and will push the throttles fully forward.
https://youtu.be/9Ts_AjU89Qk?t=1253

Posted by: Peter AU 1 | Mar 21, 2019 8:21:54 AM | 140

I think we will find that MCAS also affects centering and feel of the elevator. MCAS is software incorporated int the flight control computers which in turn are connected to the elevator centering and feel computer.

https://www.facebook.com/B737Theory/posts/the-feel-diff-press-indication-on-the-flight-control-panel-can-illuminate-in-the/604444189584201/
"3. The third is related to the Stall Management and Yaw Damper (SMYD), and a so called Elevator Feel Shift module (EFS), which creates a ±4 times higher forward control column force when approaching the stall region. This force uses a reduced system A pressure and when this reducer fails..."

https://www.slideshare.net/theoryce/b737-ng-flight-controls
>29. Elevator Neutral Shift The stabilizer controlled elevator neutral shift function changes the neutral position of the elevators during stabilizer movement. The stabilizer moves elevator neutral shift rods. The neutral shift rods provide an input to the elevators through the Mach trim actuator and the feel and centring unit, When the feel and centring unit moves it also back drives the control cables which move the control columns to their new neutral position. The elevator is drooped 4 degrees when the stabilizer is at the neutral trim position indicated as 4 units of trim. When the stabilizer moves in either direction from neutral position, The elevators move up this is true with flaps UP. FCC Controlled Neutral Shift Functional The primary function of the flight control computer (FCC) controlled neutral shift is to reduce the pilot column force necessary to trim the airplane during initial climb out after takeoff with a forward CG and both engines operating. The FCCs provide inputs to the Mach trim actuator. The incremental elevator input commanded by the FCC controlled neutral shift varies with flap and stabilizer position. Very simply with flaps not up the combined FCC and stabiliser neutral shift function moves the elevators down with the stabiliser set between 0 and about 7 units. From 7 units to 16.9 units or maximum Nose up trim the elevators move UP Note. Trim 0 is maximum stabiliser L.E. Up or Nose down trim for Aft C. G. Trim 16.9 is maximum L.E Down or Nose UP trim for forward CG. Note. Manual trim wheel inputs, autopilot, and speed trim will not command elevator movement by the FCC controlled neutral shift function."

Posted by: Peter AU 1 | Mar 21, 2019 10:27:45 AM | 141

@Vasco da Gama #117

You two quotes do not contradict one another, so if anyone was trolling it was you.

You are implying that "having apple" and "eating apple "is one and the same thing, but you avoid bein explicit about it. Quite a trolling.

Posted by: Arioch | Mar 22, 2019 11:58:21 AM | 142

The aircraft DOES have two sensors measuring independently the same aspect of reality.
That IS the redundancy - two independent unit doing the same work.
Posted by: Arioch | Mar 19, 2019 12:04:55 PM | 113

Redundancy is a safety factor, it has no other relevance. Basing critical automated actions on the signal output from a single sensor is irresponsible and should never have been approved.

The output from the second sensor is not connected to the active flight control computer, therefore it provides NO redundant data to the flight control computer. Therefore there are not two independent units doing the same work - there is one unit doing some work while the other unit is doing nothing. That is not redundancy. You are abusing the word redundancy.

Posted by: BM | Mar 22, 2019 2:27:12 PM | 143

Posted by: Arioch | Mar 22, 2019 11:58:21 AM | 143

It is just that you had already shown you could understand the concept Arioch. Insisting on the meaningless side did not suit you. BM, between us just stressed the important part.

Posted by: Vasco da Gama | Mar 22, 2019 3:05:26 PM | 144

Posted by: PavewayIV | Mar 19, 2019 10:31:07 PM | 124

From that link to the Indonesian black box you posted Paveway IV, there is something funny about the AoA sensors. It is not clear from the diagram what is diagrammatic convention/artifact and what is aberration.

In the first segment of the data, before takeoff, where the text label states "Angle of Attack sensors", the left and right sensors are separated by a certain distance - about 13 on the calibrated scale but that is just an arbitrary number. Shortly after the label text, but still BEFORE takeoff, the left signal rises, increasing the separation to about 20, then shortly after increases again to about 27. All this is before takeoff, and all this time the right sensor is absolutely constant. A fraction before starting to move the right sensor then INCREASES by about 3 units, and at the same time the left sensor DECREASES by about the same amount. From this moment until takeoff the right sensor is flat, while the left is increasing very very slightly. From the moment of takeoff the two sensors seem perfectly syncronised, yet the separation of the two sensors (about 20) is significantly greater than at the start (Angle of Attack sensors label). Is this a real effect or is it just an artifact of the way the plot is drawn to combine different data in one plot?

One possible explanation for the strange behaviour before takeoff is that while at rest the two sensors are in random positions because there is no airspeed, and therefore when stationary both sensors give invalid data. Also the left sensor might be moved by a cross-wind coming from the left; once the plane is moving the cross-wind will have no significant effect on the sensor. If this is true, then what is interesting is that both signals seem to give the same data, which also appears in approximate agreement with the (somewhat averaged) nose pitch position data - i.e. suggesting in this case that both sensors were working normally. Still unclear is whether the separation of the two plots is correct during the flight (i.e. working) or at time zero (meaning a zero-error in one of the sensors). Also not clear from the diagram is whether the left or right sensor is the one being used for the flight control data.

Posted by: BM | Mar 22, 2019 3:14:04 PM | 145

Bjorn’s Corner: Why did Ethiopian Airlines ET302 and Lion Air JT610 crash?

The author advances the hypothesis of blowback:

I know from pilots who have tested to fly a 737 in the simulator that you can keep the nose up with the Pilot controlled elevator, even against a full nose down trimmed horizontal stabilizer.
(...)
We know this for sure [pull the collumn for elevator up] for JT610 where we have the Column force traces (C in Figure 2) and can assume this for ET302.
(...)
Blowback means the elevator is gradually blown back to lower and lower elevation angles by the pressure of the air as the speed increases. The hydraulic actuators can’t overcome the force of the air and gradually back down if the force of the air grows too strong.

If a blowback phenomenon is confirmed for the 737 at the speeds and altitudes flown, this is what happened at the end of the JT610 flight and probably ET302.

But I'll introduce the variation: maybe the pilots were successful in the simulator simply because it was built according to FAA specs (as opposed to the real aircraft specs), and as we now know, "MCAS was capable of moving the tail more than four times farther" (2.5 instead of 0.6), in which case the maximum elevator effect would then become insufficient to overcome the actual stabilizer position.

Posted by: Vasco da Gama | Mar 22, 2019 3:38:28 PM | 146

The newspaper article makes it pretty clear that the FAA has put Boeing in the pilots seat of aircraft approval in similar fashion to how the FDA has put pharmaceutical companies in an even deadlier position with respect to drugs that are prescribed to more people than will ever be on a Boeing product of any kind. If everything is it is should be, this should be an early notice that Boeing is in a similar situation as a result of the 737 MAX 8 as Monsanto/Bayer is with glyphosate. Let the lawsuits begin.

Posted by: Vonu | Mar 22, 2019 5:49:18 PM | 147

The two flight control computers do cross check most sensor inputs. Why not the AOA sensors. I think they do, but rather than showing a warning of a discrepancy, MCAS is delegated to the computer showing worst case scenario. The FCC's are supposed take turns running MCAS, one computer runs in one flight the runs it next flight but with lion air it did not do this. Also it is not just AOA but also airspeed indicator on captains side was faulty. As the AOA sensor had been replaced and had not fixed the problem, he fault is more likely to be in the software.

Posted by: Peter AU 1 | Mar 22, 2019 6:15:37 PM | 148

@ 61

"So, again, like the misdocumentation, hints at last-time effort to devise any "ugly fix" to patch up the glaring problem, with no time left to think about quality or reliability."

" And no man putteth new wine into old bottles: else the new wine doth burst
the bottles, and the wine is spilled, and the bottles will be marred: but new
wine must be put into new bottles." From the Revelation

The system, of wich Boeing is a part, is in a state of collapse, the snake is unaware that it is consuming itself. Only a radical transformation will save the day.

" And I saw a new heaven and a new earth: for the first heaven and the first
earth were passed away; and there was no more sea." From the Revelation

For those who are not afraid to face reality the following links:

http://www.marques.co.za/duke/debate.html

http://www.marques.co.za/duke/zero.html

https://www.youtube.com/watch?v=QBLlf0FpsOc&index=19&list=PLnhtWZzOWMck75TKVtX9E-FyHXrt_Hgir

Posted by: d | Mar 23, 2019 1:56:36 AM | 149


John 10:20 King James Version (KJV)

20 And many of them said, He hath a devil, and is mad; why hear ye him?

The faithful witness

Posted by: Duke | Mar 24, 2019 12:22:49 AM | 150

https://www.reuters.com/article/us-ethiopia-airplane-investigators/investigators-believe-anti-stall-system-activated-in-ethiopian-crash-wsj-idUSKCN1RA0E1?il=0
"U.S. and European regulators knew at least two years before the Indonesian crash that the usual method for controlling the 737 MAX’s nose angle might not work in conditions similar to those in two recent disasters, Reuters reported on Friday, citing a document."

Posted by: Peter AU 1 | Mar 29, 2019 3:24:59 AM | 151

It gets worse. Via Sputnik today:

Another report, cited by Reuters and The Wall Street Journal, states that the aircrew followed procedures laid out by Boeing following the crash of a Lion Air 737 MAX in October and disabled the MCAS, however, the system was activated at least three times—and at least one time after the pilots followed the correct steps to shut it down.

It is not clear at this point whether the pilots purposely reactivated the MCAS’ stabilizer control or if the software reactivated on its own after shutdown. A source told the Wall Street Journal that it appeared the pilots turned the system back on hoping to regain control over the stabilizers, yet Reuters reported that the software may have reactivated without human intervention, and further investigations of that possibility are ongoing.

Ethiopian Airlines Boeing 737 Max Was Struck by 'Foreign Object' - Reports

Posted by: Petri Krohn | Apr 4, 2019 4:22:40 AM | 152

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