Ethiopian airliner down in Africa

[jimtx]

Originally Posted by A0283

@FCeng84 - I really appreciate your effort to help clarify a number of issues. Hope Boeing will elaborate on this in the end ;-)

For me there is a difference between an "AoA increase" and a "positive AoA rate". Hope you can clarify that during your further explanations.

I was wondering if you were talking about "positional feedback" with MCAS or "force feedback" or both. In another explanation you exclude the "positional".

If you use the cutout and remove the power you disable MCAS ... which would put you outside the 'normal' certified envelope... do I read that correctly? ... With MCAS aimed at the NNC part of things, using the cutout appears to push you in yet again an other area, and outside certification?... Or is that a wrong interpretation?

I think you would be correct but the NNC given by Boeing/FAA does not caution you to avoid whatever regime MCAS was designed to protect against. Takeaway being why have MCAS in the first place? Yes, I know, certification pencil whip.

[LEOCh]

Originally Posted by FCeng84

Pitching moment caused by engine thrust is a function of how much thrust and where the engine is mounted vertically with respect to the center of gravity. Thrust pitching moment is not a function of how far forward or aft the engine is located. With this in mind, the nose up thrust induced pitching moment generated by the 737MAX engine is not greater than that for a 737NG. In fact, it is probably less as the center line of the larger MAX engine is higher than the center line of the smaller NG engine given their respective attachment geometries.

Hopefully it is now clear that the pitching moment of concern with the 737MAX engines that gives rise to the need for MCAS is related to the aerodynamic impact of the engine cowling location and geometry, not the magnitude nor location of the thrust vector generated by those engines.

To add a bit to this good explanation, Bjorn at Leeham news (who wrote a very good explanation of MCAS after Lionair) has a good followup that is available by googling "Bjorn's corner: Pitch stability, Part 10. Wrap up". (The previous parts are worth reading also). He is suggesting the augmented versus augmented MAX Cm (moment coefficient) versus alpha (AoA) curve would likely look similar to the one below. These curves are easy to interpret, a stable aircraft has a negative sloped curve where the pitching moment coefficient decreases as AoA increases. The interesting thing is that the unaugmented aircraft transitions between stable and less stable during prestall (and is never neutral or unstable), but the discontinuity is the problem. Although the aircraft still requires an increase in pull force to further increase AoA (It won't start increasing AoA by itself with no further pull at constant thrust), it will feel easier for the pilot than in the NG to get from pre-stall to stall.

Figure 1. A thought pitch moment curve for Boeing’s 737 MAX. Source: Leeham Co.

[retiredmecheng]

Different but similar failures in US

First time poster here, and not a pilot, but... I just noticed this in an article on the Guardian. Doesn't sound like MCAS, but perhaps another example of "un-wanted" automation trying to bring a plane down. Apologies if this has been posted before, but I haven't seen it yet on this (fascinating) thread...

"Two US airline pilots filed voluntary safety reports last year to a database compiled by Nasa, saying an automated system seemed to cause their 737 Max planes to tilt down suddenly.

The pilots said that soon after engaging the autopilot on Max 8 planes, the nose tilted down sharply. In both cases, they recovered quickly after disconnecting the autopilot.

The problem did not appear related to the automated anti-stall system that is suspected of contributing to a deadly October crash in Indonesia."

[Sailvi767]

Originally Posted by 42...

Disagree, the 737 sim felt like a as fully stalled F15C at extreme AOA as I've felt, violent shaking would be a good description. Yet, controllable. So yes, the 737 is certified to full stall, with devices in place to avoid that condition. The MCAS is only designed to modify characteristics to make it more like the NG, not stop a stall, which apparently has gone horribly wrong.

It’s nothing more than a guess on how the aircraft might react since they don’t do enough testing flight in that regime if any to provide data to build a profile for the sim.

[WingNut60]

Not unexpected, and these movements can reverse as quickly as they occur, but ;

Boeing fell 6 percent to $375.92 at 2:09 p.m. in New York.
The company has lost about $27 billion in market value this week.

[wetbehindear]

CRM vs ERM

When CRM fails, we harshly and rightly so admonish pilots.

AFAIK Amsterdam and LionAir accidents are both single channel/sensor accidents.

Is it possile to say that Boeing failed in ERM ?

(Equipment Resources Managment, failing to put good use of equipment already onboard.)

[Rananim]

I was sick the day they taught aerodynamics at flight
school but.....with FCENG84s help this MCAS is becoming a
lot clearer.It seems they wont be allowing the pilot to
inhibit MCAS using the stick when they make their software changes.
They obviously cant.
So the only thing that makes sense now is they wire up both AoA
indicators to MCAS and if they both agree and show high AoA
then MCAS can let rip.
This will for sure decrease the odds of an unwanted MCAS event.

FCENG84 has helped steady the ship here and calmed the
hysteria but ......what about Jodels scenario of a flapless
landing on a MAX with a birdstrike at 200
feet on finals followed by an MCAS runaway?What then?
The NG was as far as they should have taken that 1960's airframe/geometry....quit while you're ahead I say

[FanControl]

Currently the Max -9 has (9) in flight. The Max-8 has (97) in flight.

[edmundronald]

The really shocking takeaway from AF447 was that first world pilots, selected and trained by the country that built the plane were completely inadequate at hand-flying the plane. The training system was shown to be in need of improvement.

With the 737-Max the takeaway seems to be that the US FAA certification system is badly broken, has become beholden to the industry and is in need of improvement.

Edmund.

[jimwalsh]

Originally Posted by FanControl

Currently the Max -9 has (9) in flight. The Max-8 has (97) in flight.

Now down to 10 (8 in NA) Max-9 and 56 (48 in NA) Max 8

[CaptainProp]

Originally Posted by Tryingharder

Sorry to intrude here, just a passenger, but I'm baffled what risk assessment in a safety critical industry means that an aircraft that is already airborne needs to find a destination other than the one it was planning to go to in the UK?

I appreciate the fact that the type is effectively prohibited from UK/European airspace but surely asking the crew to go hawking around the world looking for a diversion is introducing additional risk to the baseline risk now associated with this aircraft rather than reducing it. It's got to land somewhere right? And even if it's going to go wrong it's better it goes wrong with every potential advantage in the crew's favour even if that's only ATC in English and familiar with the terrain at a familiar airport. As opposed to an unfamiliar airport with altitude / temperature that might even predispose to the failure condition being encountered after wandering round introducing additional constraints such as fuel.

I apologise if that risk assessment was done today on the basis of the weather in the UK being a risk - but I can't see it.

I work in a safety critical business; medical devices. If I know there's a safety advisory on a piece of kit then I'll risk assess the likelihood/impact of keeping it in service vs the benefit to the patient. That's a very different conversation when the operation's not started (on the ground) vs patient "on the table" (aircraft airborne). And sometimes we might be "brave" when the patient really needs it.

Just askin'

You are correct. It’s called @ss covering bureaucracy where common sense and rational thinking unfortunately often has no place.

CP

[cncpc]

Originally Posted by retiredmecheng

First time poster here, and not a pilot, but... I just noticed this in an article on the Guardian. Doesn't sound like MCAS, but perhaps another example of "un-wanted" automation trying to bring a plane down. Apologies if this has been posted before, but I haven't seen it yet on this (fascinating) thread...

"Two US airline pilots filed voluntary safety reports last year to a database compiled by Nasa, saying an automated system seemed to cause their 737 Max planes to tilt down suddenly.

The pilots said that soon after engaging the autopilot on Max 8 planes, the nose tilted down sharply. In both cases, they recovered quickly after disconnecting the autopilot.

The problem did not appear related to the automated anti-stall system that is suspected of contributing to a deadly October crash in Indonesia."

I saw that on Rachel Maddow tonight. I agree that this doesn't seem to be MCAS related, given that MCAS doesn't activate when the AP is on. Depending on how out of trim the aircraft is when the autopilot is turned on, it might well command nose down.

[hans brinker]

Originally Posted by positiverate20

No idea how to retrieve a 20 minute post I'd written- where does the "Auto-save" go??

Anyway, quickly, and quite ironically, I was explaining that I've little to no "software coding" literacy nor any in-depth knowledge as to how it works.

My point was basically (acknowledging this is off-topic at this stage for flight in question, but in same tangent as previous MCAS discussion):

We know, with Lion Air anyway, MCAS caused problems.
We know MCAS failed- in that it wasn't designed to have the effects that it had.
With this in mind, how can we be so confident that MCAS adhered to:
- the pitch limitations
- the 10 seconds of operation
- the 5 seconds 'wait and see' period
- not functioning if flaps extended
etc. etc.

My point was- if the system failed- how, at this stage anyway, can anyone be certain that one component of the system failed entirely and that every other single component performed perfectly? Despite whatever failure mode it's in, does it still adhere to the pitch input rates, same operating window etc.?

I'm more comfortable with hardware, because I understand it, and know how it can fail- which is why it shocks me that the MCAS system is dependent on one single AoA vane's data- ludicrous. However, we can't at this stage determine the hardware was the only fault for Lion Air, are there other flaws or weaknesses hidden in the software, circuitry, functioning, logic of the MCAS elsewhere? Maybe MCAS was never an issue? Maybe errant data from a faulty ASI corrupted the MCAS or made it behave erratically?

I'm uncomfortable with the encroachment and infringement of automation by way of control inputs during what was considered to be manual flight. It frightens me that even with all AP functions off, computer software can still manipulate controls in this way.

Actually MCAS functioned as it was supposed to in the Lion Air crash, it received a high AOA signal and kept trimmed accordingly. The broken part was the AOA sensor. There's no need to be afraid of computers adding control inputs with the auto pilot off, the 320 does it all the time and has half the hill loss rate of the 737.

[Pearly White]

Eyewitnesses say they saw a trail of smoke, sparks and debris as the plane nosedived. https://www.bbc.com/news/world-asia-47536502

Does that really sound like an MCAS event?

[Lonewolf_50]

Originally Posted by cncpc

I saw that on Rachel Maddow tonight. I agree that this doesn't seem to be MCAS related, given that MCAS doesn't activate when the AP is on. Depending on how out of trim the aircraft is when the autopilot is turned on, it might well command nose down.

By "it" do you mean the MCAS or the autopilot (as an entity that has a bunch of sub-elements). Your point on possible out-of-trim taken on board.

[acad_l]

Originally Posted by hans brinker

Actually MCAS functioned as it was supposed to in the Lion Air crash, it received a high AOA signal and kept trimmed accordingly. The broken part was the AOA sensor. There's no need to be afraid of computers adding control inputs with the auto pilot off, the 320 does it all the time and has half the hill loss rate of the 737.

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

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

[rh2600]

If ever you wanted a good example of regulatory capture, the continuum with China sitting at one side champing at the bit to throw at stone at a US company at the first hint of smoke, and the FAA sitting right at the other holding fast while everyone else sees a fire is a pretty great illustration of the effect.

[A30_737_AEWC]

Originally Posted by threemiles

FAA says when then new MCAS software is certified and out it shall be implemented by an AD Note. I am not sure this is the right sequence if FAA feels something is very critical. Because the interim AD had nothing in it but hot air it reads like the MCAS problem is minor. Now they say it deserves implementation of the fix by AD note not by Service Bulletin. Again, this smells and the FAA does not seem to act logical and independantly but rather as the long arm of Boeing and US commercial interests. A logical step would be a grounding order by FAA until the fix can be implemented.

A Service Bulletin (SB) is the means by which the manufacturer embodies the necessary instructions for implementing the modification or for continued airworthiness. It identifies all the technical and engineering data necessary for implementation.

An Airworthiness Directive (AD) is an instrument issued by a national airworthiness authority (like the FAA) which usually identifies the applicable SB to be enacted, and a time by which it must be incorporated and/or any exceptions. It is a legal document in the context of a nation's airworthiness system and typically carries a responsibility for an aircraft operator/owner to comply with. A manufacturer's SB is not.

[bunk exceeder]

So its a stick pusher that pushes the stick. Plain English please.

[FCeng84]

Originally Posted by A0283

@FCeng84 - I really appreciate your effort to help clarify a number of issues. Hope Boeing will elaborate on this in the end ;-)

For me there is a difference between an "AoA increase" and a "positive AoA rate". Hope you can clarify that during your further explanations.

I was wondering if you were talking about "positional feedback" with MCAS or "force feedback" or both. In another explanation you exclude the "positional".

If you use the cutout and remove the power you disable MCAS ... which would put you outside the 'normal' certified envelope... do I read that correctly? ... With MCAS aimed at the NNC part of things, using the cutout appears to push you in yet again an other area, and outside certification?... Or is that a wrong interpretation?

Please excuse that I don't recall the context for "AoA increase" and "positive AoA rate". Can you point me in the right direction for that?

MCAS acts only to move the stabilizer an increment in the airplane nose down direction and then (if AOA decreases below the MCAS activation AOA threshold and the pilot has not provided an electric trim command) to take that increment of stabilizer out (i.e., run the stab airplane nose up the same amount). I don't see how this translates to "positional feedback" or "force feedback".

I think your last paragraph above gets at the issue of hazard levels, hazard mitigations, and availability of those mitigations. MCAS is implemented to address a handling qualities deficiency. The hazard level of not having MCAS drives the requirement for MCAS availability. Any failure that renders MCAS inoperative or leads to MCAS behavior for which the crew is expected to deactivate MCAS must have a probability that is low enough to permit loss of MCAS.