Ethiopian Airlines Crash; Another 737 Max

On AviationWeek today (requires free account)

http://aviationweek.com/commercial-...ds-mcas-demos-speed-lifting-737-max-grounding

Informative, especially Boeing’s quoted, on the record responses.

Three things I took away:

1) It appears MCAS will activate beginning at 20* nose up AoA, maybe lower.

2) Boeing’s quoted comments appear to have had both a legal and corp comm review.

3) The proposed changes are intended to result in bad AoA data not turning into a helmet fire.
 
On a 737: how is stick force transmitted to the flight crew? It isn't a direct coupling like a 172, it has hydraulics between the column and tail...doesn't it?

I'm wondering why stick forces would ever be so strong they couldn't be overcome, like power steering, and be pulled to the stops? I thought I read, somewhere in this thread, that hundreds of pounds of force might have been necessary, that seems excessive, but I don't understand how all the feedback systems work.
 
LongRoadBob said:
I sure don't know, but from some of the information here, it seems as if it is survivable IF certain conditions are not present.
That bit about the forces being too great to muscle if the trim is stopped at certain points, etc.
Also, I linked previously to information about a bug found in the flaps software.

I think the nose up tendancy is troubling, in the design, and software to correct it.
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There are several planes that are literally unflyable without a computer, including some fighters. I've no issue with computers figuring out how to implement the pilot's commands.
 
Like I said before stick forces are simulated by the elevator feel computer which has it's own independent airspeed sensor (pitot tube)
 
Silvaire said:
Like I said before stick forces are simulated by the elevator feel computer which has it's own independent airspeed sensor (pitot tube)
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If there's an elevator feel computer why did they need to invent MCAS to increase the control pressure?
 
dmspilot said:
If there's an elevator feel computer why did they need to invent MCAS to increase the control pressure?
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Regulatory requirement to maintain the 737 type certification due to non-linear control forces without MCAS.
 
flyingcheesehead said:
Well, *something* happened to one of the AoA vanes. That has nothing to do with the pilots or their nationality.
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This is why God created air accident investigations. You are assuming facts not in evidence.
 
TCABM said:
Regulatory requirement to maintain the 737 type certification due to non-linear control forces without MCAS.
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I guess I'm trying to ask is why the elevator feel computer couldn't be modified to do that.
 
dmspilot said:
If there's an elevator feel computer why did they need to invent MCAS to increase the control pressure?
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The elevator feel computer is not exactly what you might be thinking, it's basically a mechanical device in the tail and senses only airspeed through it's own independent devices, it has no knowledge of AOA. All large airliners have them. Without it you would wildly over-control the tail at higher speeds.
 
Chip Sylverne said:
Sure it is. If the thrust line/cg relationship isn't what it is, there would be no need for MCAS.
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light pitch control forces might "feel" like a CG issue....but it wasn't a CG issue. Irregardless of the actual CG the control forces can be whatever the designer chooses....and there is a range that's spec'd out....hence the reason for MCAS on several other models of Boeing aircraft.
 
Checkout_my_Six said:
....hence the reason for MCAS on several other models of Boeing aircraft.
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Interesting. Which models have it? I’m typed on the 757, 767, and 777 and as far as our manuals say (which we now know doesn’t mean much) none of them have the MCAS system like the Max has. The 777 has some pitch protection systems, but nothing like the MCAS.
 
Checkout_my_Six said:
light pitch control forces might "feel" like a CG issue....but it wasn't a CG issue. Irregardless of the actual CG the control forces can be whatever the designer chooses....and there is a range that's spec'd out....hence the reason for MCAS on several other models of Boeing aircraft.
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Ok, it's not a cg problem in the classical weight distribution sense of stability. It's a thrust line in relation to cg that results in the non-linear pitch forces problem.
 
So, I lost track of this thread...but has it been discussed yet that the flights would have been ok if only they had an AOA sensor?
 
bflynn said:
So, I lost track of this thread...but has it been discussed yet that the flights would have been ok if only they had an AOA sensor?
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Well technically they had it, but needed it to be working.
 
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Sluggo63 said:
Interesting. Which models have it? I’m typed on the 757, 767, and 777 and as far as our manuals say (which we now know doesn’t mean much) none of them have the MCAS system like the Max has. The 777 has some pitch protection systems, but nothing like the MCAS.
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Pretty certain it’s only the three Max variants.
 
Chip Sylverne said:
Ok, it's not a cg problem in the classical weight distribution sense of stability. It's a thrust line in relation to cg that results in the non-linear pitch forces problem.
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I'd call it a control forces issue in that configuration.....controlability.
 
Sluggo63 said:
Interesting. Which models have it? I’m typed on the 757, 767, and 777 and as far as our manuals say (which we now know doesn’t mean much) none of them have the MCAS system like the Max has. The 777 has some pitch protection systems, but nothing like the MCAS.
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It's in there Capn....you just don't know bout it. ;)
 
Checkout_my_Six said:
It's in there Capn....you just don't know bout it. ;)
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A year ago, I would have said “no way,” it’s not in the manual, it’s not on the jet. Now seeing that Boeing has been playing fast and loose with what systems they decide to document, it wouldn’t surprise me. But... I still think we don’t have it on the 757/767. With all this brouhaha surrounding the MCAS, I’m sure if one of our fleets had it, Boeing would have put out an emergency bulletin explicitly describing what types use MCAS, if any. The fact I haven’t seen an FCIF yet telling me that my aircraft has MCAS leads me to believe that we don’t have it. Nor does the 76 or the 777. But, who knows at this point. I’ll see if I had email our fleet test pilots and see.
 
Checkout_my_Six said:
so you think you know that thing down to the code level?......lol :D
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No, of course not. Neither do you, I’m sure. I’m guessing the Boeing test pilots don’t even have that kind of base programming knowledge. I bet the only ones that know those airplanes down to the code level are the software engineers themselves.

But, seeing all the bad press Boeing has gotten for not putting a major system into the flight manuals, nor even letting the pilots know about it, I’m pretty confident that if ANY of their aircraft variants out there had a system similar to the MCAS they would be scrambling to ensure every operator of those fleet types now knew about it and it was trickled down to us, the end users.
 
Checkout_my_Six said:
so you think you know that thing down to the code level?......lol :D
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Here’s the thing. The code probably isn’t the issue. The issue appears to be what the logic tree is when erroneous information is fed to it.

That’s the bigger challenge Boeing has to overcome. Notice there’s been more than a couple who have fully trusted Boeing has provided them with the information necessary to successfully recover from abnormal conditions occurred during flight.

That trust was broken with the revelation of MCAS in the 737, after the fact.

Had Boeing applied the rigor we’re seeing now in the immediate aftermath of the Lion Air crash, it’d be a different story.
 
bflynn said:
So, I lost track of this thread...but has it been discussed yet that the flights would have been ok if only they had an AOA sensor?
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TCABM said:
Well technically they had it, but needed it to be working.
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I think Mr. Flynn was making a joke based on previous threads in which AoA sensors were being touted for GA aircraft.

Yours truly,
Lieutenant Obvious
 
Palmpilot said:
I think Mr. Flynn was making a joke based on previous threads in which AoA sensors were being touted for GA aircraft.

Yours truly,
Lieutenant Obvious
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I know. Tried to extend the play and failed.
 
Piperonca said:
Focus on the pilots in this article.
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And the discussion continues to expand to include the certification side as well as the pilot side. Here's one example:

POST:
"The source indicates the crew appeared to be overwhelmed and, in a high workload environment, may not have followed the recommended procedures for re-trimming. Boeing’s stabilizer runaway checklist’s second step directs pilots to “control aircraft pitch attitude manually with control column and main electric trim as needed,” according to one U.S. airline’s manual reviewed by Aviation Week. If the runaway condition persists, the cut-out switches should be toggled, the checklist says."
REPLY
"The certification process relies on crews 'flying the plane' (see magenta line video) when something goes awry. All systems eventually rely on giving the bag of bolts to the flight crew - that's what alternate and direct law are about in A and it is why the flight crew are there. It was expected that a response to inappropriate MCAS would be autopilot off, autothrottle off, manual trim to correct to neutral trim then stab trim off and fly the plane. Perhaps certification should not rely on the crews following these NNC and other checklists? That is a big can of worms and leads to autonomous aircraft that can handle non-nominal cases that the crew were there to handle."
 
Counterpoint to the seekingalpha piece from another pprune post, and good questions to ask:


Totally agree that this is an effort to build the public opinion case for pilot error. I find it quite remarkable that it takes such a long windup to finally conclude that the crew did not do everything perfectly. Duh. No human ever does.

And then it just stops. What is the point of finger-pointing? How can that help anyone in any way? (Except perhaps Boeing's reputation, but even that is doubtful.)

A finding of "Human Error", can never be the end of an analysis, rather it must be the start of asking questions such as:
  • What was the exact situation the operators were in?
  • What was the information they could get?
  • Was some information maybe ambiguous? Even contradictory? Hard to find?
  • How much time did they have to find it?
  • How much time did they have to analyse it?
  • Were they trained to evaluate the information properly?
  • Were there perhaps multiple anomalies requiring different, possibly even contradictory procedures?
  • Was there perhaps cognitive overload?
  • Did they (could they?) have an understanding of why the system did what it did?
  • What additional information do we have now, that the operators at the time did not have? (The easy one: we know that what they did eventually led to an unrecoverable situation. They didn't. Or else they wouldn't have done it.)
  • Which again leads to: why did they do what they did?
  • How can we prevent:
    • ... crews from doing the same things again, or better still:
    • ... anyone from getting into the situation in the first place?
 
Piperonca said:
https://seekingalpha.com/instablog/...930-boeing-737-max-8-crashes-case-pilot-error
Focus on the pilots in this article.
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I’m not surprised an investment advice website would be producing an opinion piece to support or counter whatever position the advice they’re giving is.

https://seekingalpha.com/article/4253912-boeing-still-safe-buy

Especially when both authors are Boeing drivers, and at least one of them has his own financial analysis firm, focusing on the aviation industry.

Interestingly enough, that guy doesn’t hold a CFP designation, so has no real fiduciary responsibility.
 
Palmpilot said:
I think I've heard that there are jet fighters that would be unflyable without software.
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I’m thinking that jet fighter pilots are more the cream of the crop. I don’t think that is a standard that can be expected from all commercial airline pilots, throughout their whole career that can be expected. I know there are automated systems on airliners, but this seems unconventional and not necessarily well thought out, as well as bugs reported.
There is a level of ability and competence expected, and many airline pilots are former jet fighter pilots I understand but with so many pilots, this seems to an outsider to be on the edge of responsible.

With more and more automation, the code becomes more and more complex as it is tasked with mor and more of the responsibility. As a programmer, I know testing has to be rigorous and honest. And even then there will be mistakes.
 
....and the job of the test pilot is to ensure all "safety critical" permutations are discovered...;)
 
Checkout_my_Six said:
....and the job of the test pilot is to ensure all "safety critical" permutations are discovered...;)
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Must be tough to be a test pilot when even you are kept in the dark about what the airplane has installed.

“Therein lies the issue with the design change: Those pitch rates were never articulated to us,” said one test pilot, Matthew Menza.

Mr. Menza said he looked at documentation he still had and did not see mention of the rate of movement on MCAS. “So they certainly didn’t mention anything about pitch rates to us,” he said, “and I certainly would’ve loved to have known.”​

https://www.nytimes.com/2019/04/11/business/boeing-faa-mcas.html
 
Sluggo63 said:
Must be tough to be a test pilot when even you are kept in the dark about what the airplane has installed.

“Therein lies the issue with the design change: Those pitch rates were never articulated to us,” said one test pilot, Matthew Menza.

Mr. Menza said he looked at documentation he still had and did not see mention of the rate of movement on MCAS. “So they certainly didn’t mention anything about pitch rates to us,” he said, “and I certainly would’ve loved to have known.”​

https://www.nytimes.com/2019/04/11/business/boeing-faa-mcas.html
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From that same article, this justification doesn’t make sense to me:

“The change to MCAS didn’t trigger an additional safety assessment because it did not affect the most critical phase of flight, considered to be higher cruise speeds,” an agency spokesman said. “At lower speeds, greater control movements are often necessary.”

I’ve never considered cruise to be the most critical phase of flight, but then again, what do I know?
 
Sluggo63 said:
“Therein lies the issue with the design change: Those pitch rates were never articulated to us,” said one test pilot, Matthew Menza.
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Curious. The quote above is contrary to other references (forums, media) that the original MCAS input was limited to .6 units and it was after further flight tests the recommendation was to increase the input to 2.5 units to maintain the required linear control forces. Some more technical articles state the recommendation was by the test pilots. Maybe the above test pilot was not involved in the MCAS side of things?
 
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