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April 05, 2019

Ethiopian Airline Crash - Boeing Advice To 737 MAX Pilots Was Flawed

The preliminary report on the March 10 Ethiopian Airline crash shows that the advice given by the FAA and Boeing to 737 MAX pilots was incomplete. The pilots followed the advice but it was phyisically impossile for them to bring the plane back into a stable flight.

In October 2018 a brand new Boeing 737 MAX airplane, flown by the Indonesian Lion Air airline, crashed into the sea shortly after take off. 189 people died. An investigation found that Boeing had added a 'maneuver characteristics augmentation system' (MCAS) to the MAX that could directly influence the stabilizer, a primary flight control surfaces, but based its decisions on the input of only one sensor. When the sensor failed the system went wild and destabilized the airplane.

Neither the pilots nor the airlines knew about the system. The regulators. which certified the plane as safe to fly, were misinformed about it. They had directed Boeing to include the new system into training material for the pilots which Boeing, for commercial reasons, did not do.

After the Lion Air crash the Federal Aviation Administration issued an Airworthiness Directive 2018-23-51 which adviced 737 MAX pilots how to handle an MCAS failure.

full picture

The FAA told 737 MAX pilots to use the Stabilizer Trim Cutoff switches to interupt the power supply for the system's actuator, a motor driven jackscrew in the back of the airplane. The pilots should then use the manual trim wheels in the cockpit, which move the jackscrew and stabilizer via steel cables, to righten the aircraft.

On March 10 a 737 MAX flown by Ethiopian Airline crashed shortly after take off. 157 people died. Radar data and debris found showed that the cause was likely a similar MCAS failure as had happened on the Indonesian Lion Air flight.

All 737 MAX planes were grounded with the U.S. being the last country to order it.

Some U.S. pilots, as well as some commentators here, publicly blamed the darker skin pilots for not using the simple procedure the FAA had put out: "Why didn't they just flip the switches? Stupid undertrained third-world dudes."

It now turns out that the well trained and experienced pilots on the Ethiopian Airline flight did exactly what Boeing and the FAA told them to do. From the Ethiopean Airlines press release (pdf):

The preliminary report clearly showed that the Ethiopian Airlines pilots who were commanding Flight ET 302/10 March have followed the Boeing recommended and FAA approved emergency procedures to handle the most difficult emergency situation created on the airplane. Despite their hard work and full compliance with the emergency procedures, it was very unfortunate that they could not recover the airplane from the persistence of nose diving.

The procedure Boeing and the FAA advised to use was insufficient to bring the aircraft back under control. It was in fact impossible to recover the plane. The possibility of this to happen was discussed in pilot fora and on specialized websites for some time.

The MCAS system moves the front of the stablizer up to turn the nose of the airplane down. The plane then decends very fast. The aerodynamic forces (the "wind") pushing against the stabilizer gets so strong that a manual counter-trim becomes impossible.

Avionics engineer Peter Lemme details the physics involved in this.

via Seattle Times - full picture

Lemme concludes:

With the 737MAX cutout switches, MCAS runaway is stopped by throwing both switches, losing electric trim altogether. In this case, the flight crew must rely on manual trim via turning the trim wheel/crank. As discussed above, the manual crank can bind up, making flying much more difficult.

Bjorn Fehrm, a senior engineeer and pilot now writing at Leeham News, came to a similar conclusion:

[We] can now reveal how it’s possible the aircraft can crash despite using the Cut-Out switches. To verify, we ran it all in a simulator together with MentourPilot Youtube channel over the last days.
At a miss-trimmed Stabilator, you either have to re-engage Electric trim or off-load the Stabilator jackscrew by stick forward, creating a nose-down bunt maneuver, followed by trim.

Stick forward to trim was not an option for ET302, they were at 1,000ft above ground. According to The Wall Street Journal, the ET302 crew re-engaged electrical trim to save the situation, to get the nose up. It was their only chance. But too late. The aggressive MCAS kicked in and worsened the situation before they could counter it.

On the FAA's Airworthiness Directive Fehrm writes:

Nowhere is it described the trim could be impossible to move if the Cut-Out switches were cut at the slightest miss-trim at the speeds flown. And there is no warning on when to move the Cut-Out switches, the checklist says “Cut, then trim manually.” This is not the whole truth.

An detailed analysis of the flight recorder data as documented in the preliminary crash report confirms the conclusions:

The high speed of 340kts indicated airspeed and the trim at 2.3 units causes the Stabilator manual trim to jam, one can’t move it by hand. The crew is busy trying to hand trim the next two minutes but no trim change is achieved.

via Leeham News - bigger

The pilots then do the only thing possible. They reengage the electric stabilizer trim to righten the aircraft.

But the aggressive MCAS, trimming with a speed 50% higher than the pilot and for a full nine seconds, kicks in at 8 with a force they didn’t expect. Speed is now at 375kts and MCAS was never designed to trim at these Speed/Altitude combinations. Dynamic pressures, which governs how the aircraft reacts to control surface movements, is now almost double it was when last MCAS trimmed (Dynamic pressure increases with Speed squared).

The Pilots are thrown off their seats, hitting the cockpit roof. Look at the Pitch Attitude Disp trace and the Accel Vert trace. These are on the way to Zero G and we can see how PF loses stick pull in the process (Ctrl Column Pos L). He can barely hold on to the Yoke, let alone pull or trim against.

His reduced pull increases the pitch down further, which increases the speed even more. At 05.45.30 the Pilots have hit the seats again (Accel Vert trace and Ctrl Columns force trace) and can start pulling in a desperate last move. But it’s too late. Despite them creating the largest Control Column movement ever, pitch down attitude is only marginally affected.

The pilots and their passengers lose the fight:

It’s easy to say “Why didn’t they trim then?”. Because they are going down at 20 degrees nose down (which is a lot, a normal landing approach is 3°) and at 400kts. Then you just pull for all you have. And the aircraft is not reacting to the largest Control Column displacement since takeoff. This makes them pull even harder, the aircraft is unresponsive and they are fighting for theirs and all the passenger lives.

A diligent safety anlysis would have predicted this outcome. Neither Boeing nor the FAA seems to have done such after the first 737 MAX crashed. They provided an Airworthiness Directive with procedures that were insufficiant to correct the system induce misbehavior.

Moreover their description of the MCAS was incomplete. It is only now known that the MCAS trims the stabilizer at a speeed of 0.27 units (degrees) per second while the pilots electric trim moves the stabilizer at only 0.18 units per second:

"It's like a Tasmanian devil in there," says Dennis Tajer, a 737 pilot and communications chair for Allied Pilots Association, which represents American Airlines' pilots.
If MCAS keeps tripping, and if pilots do not shut off electric trim entirely, the result is what Tajer describes as a two-steps-back, one-step-forward scenario, with MCAS maintaining an edge.

"The MCAS knows but one speed, which is 0.27, which is the most-aggressive speed," Tajer says. "If you look at the balance sheet on it, MCAS is winning, and you are losing."

The insufficient advice to pilots given after the first crash only adds to the long list of criminal mistakes Boeing made and which the FAA allowed to pass.

Today the Washington Post reports of another software defect which the FAA demands to have fixed:

Boeing confirmed to The Washington Post that it had found a second software problem that the Federal Aviation Administration has ordered fixed — separate from the anti-stall system that is under investigation in the two crashes and is involved in the worldwide grounding of the aircraft.

That additional problem pertains to software affecting flaps and other flight-control hardware and is therefore classified as critical to flight safety, said two officials with knowledge of the investigation.

The criminals at Boeing again offer no explanation and play down the issue:

In a statement, Boeing called the additional problem “relatively minor” but did not offer details of how it affects the plane’s flight-control system. “We are taking steps to thoroughly address this relatively minor issue and already have the solution in work to do that,” it said.

What other 'features' were secretly implemented into the 737 MAX without sufficiant analysis about their side effects and consequences?

Previous Moon of Alabama posts on the 737 MAX crashes:

Posted by b on April 5, 2019 at 05:53 AM | Permalink

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@ vk | 97

Boeing is a main manufacturer for the USAA. They are more important than God in America. They'll be fine.

Sure they are, but will they?

"General Electric is a main manufacturer for the USAA. They are more important than God in America. They'll be fine."

"General Motors is a main manufacturer for the USAA. They are more important than God in America. They'll be fine."

"Ford is a main manufacturer for the USAA. They are more important than God in America. They'll be fine."

Wouldn't be so sure, but time will tell.

Posted by: Scotch Bingeington | Apr 6, 2019 11:24:10 AM | 101

Hoarsewhisperer @7 It's in fact right. In most planes the idea is for the center of lift and the center of mass to coincide or at least be very close. In the case of the 737 MAX it is apparently not so. As far as I understand the reason is the engines, and the desire to use them(bigger and probably heavier and also in a more forward position) without major redesign. The result of this arrangement is that the plane will tend to rotate in pitch without another force stabilizing it - in other words to return the plane in a state of dynamic equilibrium. If the force isn't there you get severe pitch down, if it is small than the required you get milder pitch down, if it is larger than required you get pitch up. It's very basic theoretical mechanics.

Posted by: Stan | Apr 6, 2019 11:33:38 AM | 102

Who said that?

The 757 is a joy to fly. It really is.

Posted by: Gravatomic | Apr 6, 2019 11:42:37 AM | 103

If there is a more complex set of dynamics at play in this faulty "explanation" which makes the faulty claim "true" then there's been a serious omission from the info provided.

Posted by: Hoarsewhisperer | Apr 5, 2019 7:25:59 AM | 7

I would not consider a failure of communication as "serious" as the engineering failure. But then the "more complex set of dynamics" are there. There is no omission at all: Having the aircraft "balanced"; Pitch pivot "/\" in the drawing; "center of gravity" downward force; "Lift" upward force; "horizontal tail" downward force.

You are filtering out from your interpretation the imaginary reference line of a balanced aircraft and the relative application points of the intervening forces in relation to the pivot point, it is with respect to those that the infographics mention a "nose up" and a "nose down" condition, not merely with respect to arbitrary anterior and posterior conditions. The magnitudes of those forces should balance out on level flight.
(when i was a kid i would lean forward or backward to balance ourselves horizontally against my friend's weight for the lengthiest time on a teeter-totter)

Remember the purpose of the infographic is to explain the inability of the pilots to actuate manually the horizontal stabilizer even under the small forces produced with nose down, yet still not small enough as a result of the incident air flow on the stabilizer surface, given the MCAS induced increased speed the plane was under. This indeed is the fact neglected by Boeing and the FAA on their November AD, but also on their pre-certification analysis.

Posted by: Vasco da Gama | Apr 6, 2019 1:43:46 PM | 104

@ Posted by: Scotch Bingeington | Apr 6, 2019 11:24:10 AM | 101

Oops, a typo. By "USAA", I meant "USAF". Sorry.

Posted by: vk | Apr 6, 2019 2:24:17 PM | 105

@ Posted by: Gravatomic | Apr 6, 2019 10:47:52 AM | 98

Not at all. The tendency of the profit rate to fall is simply a law of capitalism that states that, over time (of its development), capitalism will see its general rate of profit to decline.

This law is important because capitalism is a system that produces for profit, not for human needs. Without profit, it will die. So it needs constant and/or crescent profit rates to guarantee not only its reproduction, but also its expansion.

Since profit is simply value, which is human labor, it results that capitalism needs to constantly exploit human labor to survive. But just exploiting it has its limits: a day only has 24h, a human can only work hard enough until it dies of a heart attack. The solution is machines, better logistic and better infrastructure, so that humans can produce a lot of things in less time.

Exploitation of labor is a very simple concept to grasp: when you make a human being to work beyond the point at which it needs to reproduce itself as a human being, then it is producing (beyond this point) for someone else. Since humans don't exist isolated, this means the worker needs to reproduce the entire social system in order to reproduce itself.

But all this technology has a cost, which can be translated in natural resources humans take out from planet Earth and transform them into humanly useful things. The general assumption is: the more advanced technologically is a society, the more natural resources it needs to reproduce itself.

But inanimate things don't produce wealth: they can be wealth, but they don't produce it (i.e. they are not value). An inanimate thing cannot reproduce itself to human favor by itself. It needs a human working at it at least at some point of the line of production. However, the more "inanimate" the system is, the more labor time goes to reproduce the system itself and not to convert itself into profit (excess wealth). The key here is that, for capitalism, what matters is not the thing, but the process, the differential of value (i.e. if what comes out is larger than what came in).

Posted by: vk | Apr 6, 2019 2:40:17 PM | 106

Didn’t Warren Buffet say something to the effect of “Yes, it is a class war, and we have won.”? This current criminal activity is further proof. Anybody remember the Ford Pinto?

So it seems karlof1, a retired history professor (I hope I am remembering that correctly) and many others, myself included, are at the point of “it’s high time the elite began taking casualties.” I’m all for proper retribution, though my attitude towards towards the death penalty has changed in the past few years. Due to their positions and their access to a legal system designed to protect them, the only way we get the Boeing board members and engineers and FAA flunkies onto their own creation and (temporarily) into the air is at the point of many guns. This is obviously not the first mention of pitchforks and torches, and I often see where this is probably the only thing that will effect real changes. But I admit my fear of the storm that will follow the first drop of the guillotine blade, the civil war that revolutions eventually engender.

Posted by: NotBob | Apr 6, 2019 2:49:23 PM | 107

Jared @ 87:

"... But large companies are often rife with lazy and incompetent people - which is why in a free market they are always crushed by much smaller up starts ..."

Unfortunately in the "free" markets that we have, large companies grow large because they can buy up the smaller upstarts or put them out of business in various ways, such as lobbying governments to pass regulations that limit or put the competition out of business, or banding together to drive prices down that throw the smaller companies out or stop new businesses from challenging them. Or small companies, to continue to make profits, have to grow in ways to challenge larger rivals that require taking on debt (and risk their future profitability) or issue shares (which would lead to their being swallowed up by the bigger rivals). In the high school economics that I was taught, these were referred to as "barriers to entry".

If your statement were true (we wish), then all large companies would have collapsed ages ago, most of us would be working in co-operatives and the US would have broken up into much smaller entities.

Posted by: Jen | Apr 6, 2019 4:46:12 PM | 108

If half the effort put in by the democrats against Trump and Russia would be directed against the criminals at boeing, I'd be happy.

Posted by: Kaiama | Apr 6, 2019 6:29:45 PM | 109

@106 & 097 vk

Thanks for your economic analysis. And of course it's not off-topic by one particle: underneath the technical discussions of how the plane failed, the true story is how Boeing failed, and the larger picture is how modern capitalism is failing.

When we know that this has all been diagnosed and forecast long in advance, it does make sense to read the playbook. I think I'll take your advice and start exploring Das Kapital. I didn't find an easy link yet but when I do I'll share it here. If anyone has one, please feel free to share it.

Posted by: Grieved | Apr 6, 2019 7:02:31 PM | 110

re Fukushima
For another point of view on what caused the accident I suggest reading Jim Stone articles.

Posted by: frances | Apr 6, 2019 9:02:53 PM | 111

The Trueman Show 77
Ghost Ship 86

I'm saying a class war:

Boeing will survive but severely damaged for some time. There is insufficient air craft manufacture across the globe to meet demand should Boeing collapse. My assumption is that the FAA and Boeing will airbrush a fix in the public awareness and f#ck you will continue as business as usual.

Posted by: uncle tungsten | Apr 6, 2019 10:26:24 PM | 112

Marxists Internet Archive at is a great multi-language repository:

Volume I - Book One: The Process of Production of Capital
Volume II - Book II: The Process of Circulation of Capital
Volume III - The Process of Capitalist Production as a Whole

Posted by: Vasco da Gama | Apr 7, 2019 2:16:06 AM | 113

Marx's analysis of how capitalism works is essential reading even if you are a capitalist, or perhaps especially if you are a capitalist. Marx's works are the missing link that can make over the social sciences into hard sciences like physics and biology, and without which the social sciences will remain soft mush that results in such objectively and empirically worthless metaphysical nonsense as "identity politics".

I don't know that this understanding in the hands of Boeing's leadership would have saved Boeing's victims, because as vk points out above Boeing was reacting to market pressure in a perfectly normal fashion for a capitalist enterprise when it created the MAX deathtrap, just like American auto manufacturers did in the 1970s in response to market pressure from Japanese auto makers. To expect Boeing to not put its short term ability to profit and attract capital first is to assume that Boeing is something other than a capitalist enterprise. To expect the FAA to not behave likewise is to ignore that they are first and foremost an organ of imperialism (understanding of which is one of Lenin's contributions to Marxist analysis), which, by the way, makes Ethiopia's decision to outsource the flight recorder data extraction to a somewhat more neutral organization very wisely done. Those "backwards" Africans are not so stupid as corporate mass media talking heads would want the captive consumers of their infotainment products to believe.

Posted by: William Gruff | Apr 7, 2019 6:30:17 AM | 114

Remember the Mercedes A-Class? ESP alone did not fix it. The wheels had to be wider. They shoud make main wheels too higher and put engines at correct position.

Posted by: Max | Apr 7, 2019 8:16:26 AM | 115

The CEO of Boeing would be dead already in a just world, but this is not a just world and the CEO did not act alone. The problem in society is the growing minority who are willing to be corrupted at the expense of society at large. All the 'respect for the flag' is just a cover for reaming your neighbour, killing them if necessary, to make yourself successful. You see this everywhere, in the police shooting dead people rather than taking the time to resolve the situation peacefully, in the armed forces who happily kill foreigners who are no threat to the USA, it is a decay of any values in society and will never be fixed but may reset after a period of human suffering. Humans are evil and will only get worse as technology enables, especially when there is no social force to drive self improvement.

Posted by: aspnaz | Apr 7, 2019 6:45:02 PM | 116

@113 Vasco da Gama

Thank you for the great resource.

Posted by: Grieved | Apr 7, 2019 7:33:05 PM | 117

Posted by: Vasco da Gama | Apr 6, 2019 1:43:46 PM | 104
(confusing 737 MAX infographic)

Thanks for trying to clarify.
If you are saying that MCAS induced a condition in which the 'elevator' controls no longer operated normally then I "get it". If that's not what you're saying then my mental block arises from the knowledge that many thousands of 737 MAX take-offs and journeys were completed without incident or drama - presumably in every conceivable weather/ atmospheric condition and 'schedule catch-up' context.

Posted by: Hoarsewhisperer | Apr 8, 2019 10:27:47 AM | 118

Disclaimer: I am no aerodynamics engineer. Having said that I have been following both Peter Lemme and Bjorn Fehrm several takes on the issue. Bjorn particularly initiated a multi-part series on Pitch Stability beginning last November, which I recommend.

You have pinpoint where my attempt at clarification came short. It is indeed the position of the elevator in relation to the stabilizer that inhibits the use of the manual trim wheel. Not as much the stabilizer in relation to aircraft reference, as I may have suggested. At least so goes the theory, tested and verified on a B737NG instruction simulator, by MentourPilot (unfortunately he has removed his video showing this, find his own explanation why here if you are curious)

Let me rephrase your initial statement: MCAS (by trimming nose down) induced a condition (too high a speed) in which the manual trim no longer operated normally (given the elevator in opposite direction commanded by the pilot's natural reaction).

This is where the last resort "bunt" manoeuvre comes in: pilot instead of maintaining the column aft, relaxes it (also relaxing the forces applied on the stabilizer) and with haste retrims manually, pulls the column again to recover the angle of attack for a while, and repeats as many times as necessary until the aircraft is back in proper trim and AoA. This manoeuvre requires margin altitude, and balls of steel since the pilot will have to surrender horizon for ground in faith of being successful.

None of the above would be necessary if the pilot still had access to electric trim with enough authority to overcome MCAS'. By following the november AD, and by Boeing's MAX design, the pilot had neither. Its nuts!

Regarding the second part, MCAS is supposed to engage in a very narrow part of the flight envelope, namely where a stall is to be prevented, or as other opinions claim, it intervenes merely to reduce the handling difference between NG and MAX versions. Either way it is conditioned on autopilot off, flaps up and a specific Angle of Attack ( AoA <~20deg - angle below which is safe against a stall). Its engagement window is therefore limited.

The simple explanation is the failure of the AoA vane: it took 2 years of combined hours of service and cycles to incur the first instances of the menu of possible failures (bird strike, maintenance failure, etc.), and given no effective redundancy, to reveal the latent catastrophic consequence.

The lack of redundancy is absolutely nuts!

Posted by: Vasco da Gama | Apr 8, 2019 7:23:00 PM | 119

Posted by: Vasco da Gama | Apr 8, 2019 7:23:00 PM | 119

Thanks for your further patience/ persistence.
I suspect that the infographic was designed to enlighten people with a more detailed understanding of the art of airmanship than I possess. I'm also unfamiliar with the logic behind building an aircraft with a pivoting tail-plane, instead of a fixed tail-plane with elevators which, once upon a time, was considered unwise (for light aircraft) due to the risk of inducing 'porpoising'.

Posted by: Hoarsewhisperer | Apr 8, 2019 11:03:16 PM | 120

Posted by: Hoarsewhisperer | Apr 8, 2019 11:03:16 PM | 120

As it happens, my persistence appears to have been in vain. You were correct. The figure has been updated reflecting exactly your objection.

@b, perhaps for the sake of the MofA archive an update is in order?

Posted by: Vasco da Gama | Apr 9, 2019 4:42:15 AM | 121

@ Vasco da Gama

> None of the above would be necessary if the pilot still had access to electric trim with enough authority to overcome MCAS'. By following the november AD, and by Boeing's MAX design, the pilot had neither.

Reportedly the conditions when "the manual trim no longer operated normally" could happen by different ways, and MCAS only added yet-one-more.

Reportedly, "memory item says to cut off immediately, but you actually have first to level trims/stabilizer before cutting off" was a "word of wisdom" among Boeing pilots, that was never written down as official instruction.

Arguably, in emergency instructions there should be no "second thoughts" and "corner cases", there perhaps indeed should be instructions that save the day for 99% of situations at the price of dooming 1%, rather than saving all 100% of situations but only with 75% probability (figures are random).

Or maybe not.

This question seems to pre-date MCAS. MCAS only brought this to surface.

If 737 has a condition, when manual trims work no more, then demands to cut off boosted trimming are recipes for suicide.
Unless manual trimming would be somehow enhanced to work even in harshest conditions (for example, augmenting the trim wheel with insertable lever rod).

Again, this *might* be a reasonable trade-off for emergency checklists, a least unsafe last bet.
But it raises the questions about all other aspects of 737 design that can lead to such a game-of-hazard kind of emergency.

Posted by: Arioch | Apr 9, 2019 6:29:01 AM | 122

Posted by: Vasco da Gama | Apr 9, 2019 4:42:15 AM | 121
(Infographic updated)

Whew! Thank goodness.
I was beginning to wonder if aeronautical engineering had slithered into the realm of Sorcery...

Posted by: Hoarsewhisperer | Apr 9, 2019 9:52:19 AM | 123

Looking at the charts, it strikes me something as extremely simple and obvous as MCAS taking an override input from the altitude sensor (or g force sensor) would have eliminated the problem. I am absolutely aghast.

Posted by: Shyaku | Apr 10, 2019 12:29:06 PM | 124

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