MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures
Salute!
Lemme see if I understand this from a “pilot”?
So the pilots expect that pulling/pushing will override the AP or whatever by cutting out the electric trim commanded by HAL?
But we lowly pilots are not told this or even aware that a new system might be at work and what we have expected for decades is not true anymore. BEAM ME UP!
There is no reason to have an unknown system on my plane that operates in a “bang bang” mode versus a proven curve relating AoA to pitch moment and/or stick force. Oh yeah, you will encounter the black cat while the stick is shaking and you are getting warning lights about speed and such. GASP! You trim up for a second and then handle the shaker problem IAW the procedures, but the cat is still at work. A few seconds later she strikes again.
The whole thing flat out sucks. Poorly mechanized fix for an aerodynamic problem, then not come clean with FAA and then not tell the folks operating the plane.
Gotta calm down, man....
Gums rants....
Lemme see if I understand this from a “pilot”?
There is nothing sneaking through there. The cutout switch inside the column is there to prevent a trim runaway. However the MCAS as designed must function despite back pressure. If it cutout MCAS wouldn’t do its job.
But we lowly pilots are not told this or even aware that a new system might be at work and what we have expected for decades is not true anymore. BEAM ME UP!
There is no reason to have an unknown system on my plane that operates in a “bang bang” mode versus a proven curve relating AoA to pitch moment and/or stick force. Oh yeah, you will encounter the black cat while the stick is shaking and you are getting warning lights about speed and such. GASP! You trim up for a second and then handle the shaker problem IAW the procedures, but the cat is still at work. A few seconds later she strikes again.
The whole thing flat out sucks. Poorly mechanized fix for an aerodynamic problem, then not come clean with FAA and then not tell the folks operating the plane.
Gotta calm down, man....
Gums rants....
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I’m simply responding to the previous post. Forgetting about failure modes for a second, it wouldn’t make sense to have the control column cutout the trim if the pilot continues to pull back while mcas trims AND. That is the entire reason it is there. I’m talking about the MCAS functioning when it should.
Having said that, the whole thing is a goat show and there is plenty wrong. Just that isn’t it.
Having said that, the whole thing is a goat show and there is plenty wrong. Just that isn’t it.
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I am looking at what was stated, and provide the aerodynamic reasoning behind it. Forget about stick feel.
If, at high angle of attack, or low speeds, if, due to certain areas of the wing the airflow is going supersonic, the resulting lack of laminar airflow over the wing (as stated by the Boeing wind tunnel tests) induces a stall...
The aerodynamics of the engine and the wing are creating stall conditions at lower AoA and other conditions than the system is programmed for.
Look at what they tried to do, adding vortex tabs, changing the wing design....
Changing the wing design?? Do you change the wing design to make the stick pressure the same, or to prevent stall?
The differential pressure on the yoke is a RESULT of the stall.
Stick pressure? I feel that is a half baked response by Boeing to mask the problems with the aerodynamics of the wing/engine design, and simply does not make sense. Maybe that is how is was presented to the FAA, but I dont think that is reality. Boeing will never admit that the aircraft was not aerodynamically stable.
Is MCAS operational in AP? While I keep hearing the mantra, it only operation with AP off, it appears it is operational according to several reports that show turning off the AP resolves the problem. Wasnt it the case with the last crash, that when they turned AP back on, MCAS engaged again?
In one incident, an airline pilot reported that immediately after engaging the Max 8’s autopilot, the co-pilot shouted “DESCENDING,” followed by an audio cockpit warning, “DON’T SINK! DON’T SINK!”
“I immediately disconnected AP (Autopilot) (it WAS engaged as we got full horn etc.) and resumed climb,” the pilot writes in the report, which is available in a database compiled by NASA. “Now, I would generally assume it was my automation error, i.e., aircraft was trying to acquire a miss-commanded speed/no autothrottles, crossing restriction etc., but frankly neither of us could find an inappropriate setup error (not to say there wasn’t one).
In reality, MCAS is anti-stall.
If, at high angle of attack, or low speeds, if, due to certain areas of the wing the airflow is going supersonic, the resulting lack of laminar airflow over the wing (as stated by the Boeing wind tunnel tests) induces a stall...
The aerodynamics of the engine and the wing are creating stall conditions at lower AoA and other conditions than the system is programmed for.
Look at what they tried to do, adding vortex tabs, changing the wing design....
Changing the wing design?? Do you change the wing design to make the stick pressure the same, or to prevent stall?
The differential pressure on the yoke is a RESULT of the stall.
Stick pressure? I feel that is a half baked response by Boeing to mask the problems with the aerodynamics of the wing/engine design, and simply does not make sense. Maybe that is how is was presented to the FAA, but I dont think that is reality. Boeing will never admit that the aircraft was not aerodynamically stable.
Is MCAS operational in AP? While I keep hearing the mantra, it only operation with AP off, it appears it is operational according to several reports that show turning off the AP resolves the problem. Wasnt it the case with the last crash, that when they turned AP back on, MCAS engaged again?
In one incident, an airline pilot reported that immediately after engaging the Max 8’s autopilot, the co-pilot shouted “DESCENDING,” followed by an audio cockpit warning, “DON’T SINK! DON’T SINK!”
“I immediately disconnected AP (Autopilot) (it WAS engaged as we got full horn etc.) and resumed climb,” the pilot writes in the report, which is available in a database compiled by NASA. “Now, I would generally assume it was my automation error, i.e., aircraft was trying to acquire a miss-commanded speed/no autothrottles, crossing restriction etc., but frankly neither of us could find an inappropriate setup error (not to say there wasn’t one).
In reality, MCAS is anti-stall.
Last edited by Smythe; 24th Jun 2019 at 19:39.
Smythe,
You make a lot of work for people sometimes - correcting your misconceptions.
Just for now - No, MCAS is not on with Autopilot on. Only if:
AP Off
Flap Retracted
AoA high
Suggest before carrying out long winded arguments to check back through all the threads, where much is explained.
Cherrs, B
You make a lot of work for people sometimes - correcting your misconceptions.
Just for now - No, MCAS is not on with Autopilot on. Only if:
AP Off
Flap Retracted
AoA high
Suggest before carrying out long winded arguments to check back through all the threads, where much is explained.
Cherrs, B
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Really, how certain are you that it functions that way? Because Boeing stated so? How many pilot reports show that turning OFF AP resolves the situation? Lets see, to disconnect MCAS, you disconnect AP trim?
AoA high? really, how high does the AoA have to be for the wing to stall? MCAS pushes the nose down 2.5 degrees at low speeds to prevent stall? That is a hell of a different AoA on final...
Aside from that issue, what about the rest of the argument by myself and others?
Been grounded about 100 days now...just for stick feel...
AoA high? really, how high does the AoA have to be for the wing to stall? MCAS pushes the nose down 2.5 degrees at low speeds to prevent stall? That is a hell of a different AoA on final...
Aside from that issue, what about the rest of the argument by myself and others?
Been grounded about 100 days now...just for stick feel...
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Really, how certain are you that it functions that way? Because Boeing stated so? How many pilot reports show that turning OFF AP resolves the situation?
AoA high? really, how high does the AoA have to be for the wing to stall? MCAS pushes the nose down 2.5 degrees at low speeds to prevent stall? That is a hell of a different AoA on final...
Aside from that issue, what about the rest of the argument by myself and others?
AoA high? really, how high does the AoA have to be for the wing to stall? MCAS pushes the nose down 2.5 degrees at low speeds to prevent stall? That is a hell of a different AoA on final...
Aside from that issue, what about the rest of the argument by myself and others?
Yes, I am sure MCAS works that way.
The nose down upon autopilot engagement you referred to was an autopilot problem, not an MCAS problem. I've had the same thing happen on the 737NG. It's not really a big deal - just disconnect the autopilot and try the other one.
The 2.5 degree nose down trim input is actually less abrupt than the stick pusher devices installed in numerous other commercial aircraft. I assume you don't have a problem with those? The FAA and EASA certainly don't.
The 737MAX is aerodynamically stable throughout its flight envelope. Just because you want to believe otherwise doesn't make it so.
Yoko out.
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Yes, I am sure MCAS works that way.
The nose down upon autopilot engagement you referred to was an autopilot problem, not an MCAS problem. I've had the same thing happen on the 737NG. It's not really a big deal - just disconnect the autopilot and try the other one.
The 2.5 degree nose down trim input is actually less abrupt than the stick pusher devices installed in numerous other commercial aircraft. I assume you don't have a problem with those? The FAA and EASA certainly don't.
The 737MAX is aerodynamically stable throughout its flight envelope. Just because you want to believe otherwise doesn't make it so.
Yoko out.
The nose down upon autopilot engagement you referred to was an autopilot problem, not an MCAS problem. I've had the same thing happen on the 737NG. It's not really a big deal - just disconnect the autopilot and try the other one.
The 2.5 degree nose down trim input is actually less abrupt than the stick pusher devices installed in numerous other commercial aircraft. I assume you don't have a problem with those? The FAA and EASA certainly don't.
The 737MAX is aerodynamically stable throughout its flight envelope. Just because you want to believe otherwise doesn't make it so.
Yoko out.
in the congressional testimony on May 15th of Dan Elwell they bring up these other autopilot on reports in the safety reporting system. He states that these were an unrelated malfunction as yoko says. As far as everyone is aware there have been 3 cases of false MCAS. The 2 accident flights and the lion air flight before the accident. You may believe there is a cover up but that is speculation as there have not been any other validated reports
Secondly, the trim doesn’t input a reduction of 2.5 degrees to the AOA when the MCAS operates. It puts in 2.5 units of AND trim. Trim will adjust the control force requirements as we all know. Which was the goal all along.
The aircraft aren’t grounded due to stick force, they are grounded because the system designed to deal with it had major flaws in the way it was thought up and tested that led to numerous lives being lost. This is a time for reflection from all of us in the industry on how can we do better.
The autopilot does not require a consistency of feel to aid in how it will fly the airplane so the system need not function with the autopilot on. Again there has been information conveniently left out along the way these last number of months but to say it is a cover up, again is pure speculation at this point.
Last edited by ARealTimTuffy; 24th Jun 2019 at 20:24. Reason: Add
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Apples and oranges. In both accidents, MCAS activated due to an false AOA input, not because it was supposed to. An erroneous flight control input is an erroneous flight control input. This has nothing to do with aerodynamic stability.
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If our criteria is now that we can spin whatever narrative we want based on "hidden" information that no one else knows about, then this whole discussion can go very, very far out into the weeds. Personally, I'll stick to the facts as they are currently understood.
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The autopilot does not require a consistency of feel to aid in how it will fly the airplane so the system need not function with the autopilot on. Again there has been information conveniently left out along the way these last number of months but to say it is a cover up, again is pure speculation at this point.
For instance, in his introduction to the last hearing, Chairman Larsen complained that the FAA is very slow in providing documents required by the Subcommittee.
So not exactly cover up if you like, but reluctance to disclose info on the MAX certification process, lack of tranparency, dissimulation, your pick...
Maybe there's more to this MCAS business than meets PPRuNe's eyes...
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I suspect a lot of the delay has to do with the re-discovery of issues related to runaway stab trim and the quirks of the manual trim system. Much of this knowledge has been "lost" over the years, and some folks are probably learning about this for the first time.
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What facts are your referring to ?
Nobody outside Boeing and possibly the FAA actually knows why exactly MCAS was there in the first place, what exactly it was supposed to do and under what circumstances.
Apart from some unsupported declarations by non-engineer PR people, that the MCAS was supposed to do this or that, auto pilot off etc. we don't have much to understand its operation.
All we have are parts of DFDR recordings from the accidents.
Maybe talking of hard facts when speculating on what this MCAS is able to do and when exactly is a bit hard to swallow.
Nobody outside Boeing and possibly the FAA actually knows why exactly MCAS was there in the first place, what exactly it was supposed to do and under what circumstances.
Apart from some unsupported declarations by non-engineer PR people, that the MCAS was supposed to do this or that, auto pilot off etc. we don't have much to understand its operation.
All we have are parts of DFDR recordings from the accidents.
Maybe talking of hard facts when speculating on what this MCAS is able to do and when exactly is a bit hard to swallow.
Last edited by Fly Aiprt; 24th Jun 2019 at 20:59. Reason: Typo
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Nobody outside Boeing and possibly the FAA actually knows why exactly MCAS was there in the first place, what exactly it was supposed to do and under what circumstances.
Apart from some unsupported declarations by non-engineer PR people, that the MCAS was supposed to do this or that, auto pilot off etc. we don't have much to understand its operation.
Apart from some unsupported declarations by non-engineer PR people, that the MCAS was supposed to do this or that, auto pilot off etc. we don't have much to understand its operation.
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We might be speculating a bit, though ;-)
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In reading the many threads and posts, this SLF (engineer type) has what may be a yet to be discussed issue . with MCAS and the following rare scenario -
Cruise at altitude on autopilot
TCAS warning equivalent to " pull up turn left or right - now " - Does MCAS care ? Does MCAS engage ? how much change in AOA allowed before MCAS pushes nose down ?
Cruise at altitude on autopilot
TCAS warning equivalent to " pull up turn left or right - now " - Does MCAS care ? Does MCAS engage ? how much change in AOA allowed before MCAS pushes nose down ?
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You're either very bright, or posing as someone who is; it's not always obvious. Regardless, I'm scratching my head as to how you can be so sure about yourself, given that there are Boeing engineers from the MAX program who would vociferously beg to differ with what I can only assume is your opinion. So if you're going to speak with that kind of authority, you're going to need to give us something more than Boeing's official stance, as they've got a bit of a credibility problem atm.
In the mean time, the following was sent to me by one of those Boeing engineers. The last sentence says it all (emphasis added):
"I recall seeing the Cl and Cm Alpha for the MAX from the transonic test and it didn't look good. I retired shortly after that so don't know how it went from there [...] Boeing can claim it was just trying to standardize stick feel but the bottom line is that it did not meet FAA requirements for stability. I would hope that the lift and moment curves would be made public along with the results of the certification flight test. That's the only way I would feel comfortable flying on a MAX."
Let's hope that the data cited above made it to the FAA so that it can be accessed by way of a FOIA request (should it fail to be disclosed voluntarily).
The actual fact appears to be that we don't know, one way or another.
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In reading the many threads and posts, this SLF (engineer type) has what may be a yet to be discussed issue . with MCAS and the following rare scenario -
Cruise at altitude on autopilot
TCAS warning equivalent to " pull up turn left or right - now " - Does MCAS care ? Does MCAS engage ? how much change in AOA allowed before MCAS pushes nose down ?
Cruise at altitude on autopilot
TCAS warning equivalent to " pull up turn left or right - now " - Does MCAS care ? Does MCAS engage ? how much change in AOA allowed before MCAS pushes nose down ?