Indonesian aircraft missing off Jakarta
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The function of the system somewhat euphemistically named MCAS (Maneuvering Characteristics Augmentation System) is similar to that of a stickpusher. Apparently the airplane needs it to comply with certification requirements.
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Reading the letter pasted by Halfnut above my understanding is:
1. ) The Maneuvering Characteristics Augmentation System (MCAS) is a system that is distinct from the Speed Trim System (STS) and not merely an alternate name for the STS.
2.) The 737 MAX has a system whcih makes significant adjustments to the flight control system, whcih change the way the airplane flies, and Boeing provided no information on this system in operating manuals or related literature (at least to flight operations departments) .
Is this incorrect or inaccurate?
1. ) The Maneuvering Characteristics Augmentation System (MCAS) is a system that is distinct from the Speed Trim System (STS) and not merely an alternate name for the STS.
2.) The 737 MAX has a system whcih makes significant adjustments to the flight control system, whcih change the way the airplane flies, and Boeing provided no information on this system in operating manuals or related literature (at least to flight operations departments) .
Is this incorrect or inaccurate?
Last edited by A Squared; 11th Nov 2018 at 12:23.
From #978, operator system description and actions.
“… as pilots, that once we recognize the issue, we can stop the negative impacts by taking the trim system out of the loop.”
Recognition is paramount.
A pedantic Point; most of the discussion is about trim, whereas the device is an augmentation system which interfaces with trim as the output.
Questions for clarity; does the trim-wheel move when the MCAS is active? Is it a serial or parallel design ?
If no movement, then in piloting terms MCAS has no meaningful visual relationship with the conventional use of trim; thus the critical action is to take MCAS out of the loop not trim per se.
It is difficult to recognise the situation without first experiencing the out-of-trim force (in simulation, are simulators so equipped ?), and with demonstration, to understand the combinations of associated alerts, both visual and audio, so as not to confuse this specific situation with any other involving individual input failures.
There was no prior description provided for pilots. How about engineering / maintenance, or at least in a reasonable guide for troubleshooting.
Was the FAA aware; their flight ops, training, airworthiness (monitoring previous events), certification ?
Learning for safety; which was the initiating event; which were enabling factors - ‘holes in the cheese’
Regrettably this event has great learning potential for the industry; if only …
“...no matter how hard they try, humans can never be expected to out perform the system which bounds and constrains them. Organisational flaws will, sooner or later, defeat individual human performance.”
“Responsibility lies with those who could act but do not, it lies with those who could learn but do not and for those who evaluate it can add to their capacity to make interventions which might make all our lives the safer.”
Phillip Capper – ‘Systems safety in the wake of the cave creek disaster.’
“… as pilots, that once we recognize the issue, we can stop the negative impacts by taking the trim system out of the loop.”
Recognition is paramount.
A pedantic Point; most of the discussion is about trim, whereas the device is an augmentation system which interfaces with trim as the output.
Questions for clarity; does the trim-wheel move when the MCAS is active? Is it a serial or parallel design ?
If no movement, then in piloting terms MCAS has no meaningful visual relationship with the conventional use of trim; thus the critical action is to take MCAS out of the loop not trim per se.
It is difficult to recognise the situation without first experiencing the out-of-trim force (in simulation, are simulators so equipped ?), and with demonstration, to understand the combinations of associated alerts, both visual and audio, so as not to confuse this specific situation with any other involving individual input failures.
There was no prior description provided for pilots. How about engineering / maintenance, or at least in a reasonable guide for troubleshooting.
Was the FAA aware; their flight ops, training, airworthiness (monitoring previous events), certification ?
Learning for safety; which was the initiating event; which were enabling factors - ‘holes in the cheese’
Regrettably this event has great learning potential for the industry; if only …
“...no matter how hard they try, humans can never be expected to out perform the system which bounds and constrains them. Organisational flaws will, sooner or later, defeat individual human performance.”
“Responsibility lies with those who could act but do not, it lies with those who could learn but do not and for those who evaluate it can add to their capacity to make interventions which might make all our lives the safer.”
Phillip Capper – ‘Systems safety in the wake of the cave creek disaster.’
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Astonishing
That a critical control feature has apparently been undocumented/unavailable to the pilots flying the MAX.
As a long time software engineer to make these types of changes without notice to users is...not good. And my users were merely people sitting at desks, not flying planes.
I have to wonder about liability for Boeing here.
As a long time software engineer to make these types of changes without notice to users is...not good. And my users were merely people sitting at desks, not flying planes.
I have to wonder about liability for Boeing here.
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That allied pilots link
Does not show the article. Only a News archive.
...perhaps only available to members?
Also a google search cannot find a thing. So I guess this emergency directive is....secret? At least to the general public?
...perhaps only available to members?
Also a google search cannot find a thing. So I guess this emergency directive is....secret? At least to the general public?
B
That a critical control feature has apparently been undocumented/unavailable to the pilots flying the MAX.
As a long time software engineer to make these types of changes without notice to users is...not good. And my users were merely people sitting at desks, not flying planes.
I have to wonder about liability for Boeing here.
As a long time software engineer to make these types of changes without notice to users is...not good. And my users were merely people sitting at desks, not flying planes.
I have to wonder about liability for Boeing here.
“On November 6, 2018, Boeing issued an Operations Manual Bulletin (OMB) directing operators to existing flight crew procedures to address circumstances where there is erroneous input from an AOA sensor. “
Exceot for two things, the first being there is no AoA display. Second, the crew must first understand that the “existing procedures” ALSO apply to MCAS FAULT...
Trying to conflate “existing procedures” with no published link to the faulty system is dishonest and misleading.
Last edited by Concours77; 11th Nov 2018 at 12:39.
”Partial and mysterious TRIM input in manual flight”. Close to the deck, without trained response to fault.
Liability? Boy Howdy.
[QUOTE=Smott999;10308100]
It’s damning, and the lawyers who wrote it know exactly what is wrong with that statement. They also know almost all people will believe it exonerates Boeing. It won’t it digs them in deeper.
The AD is self explanatory.
it’s like they said “hey follow existing procedures” and then a couple days later it’s “oh here’s something related that we never published “
that cant be good
/QUOTEthat cant be good
It’s damning, and the lawyers who wrote it know exactly what is wrong with that statement. They also know almost all people will believe it exonerates Boeing. It won’t it digs them in deeper.
The AD is self explanatory.
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As far as I am concerned, this crash is mostly (80%) down to Boeing.... They put in some more software crap (but didn't put it in the manual), they supplied the faulty AoA sensor. And the software that allowed the faulty input to mess up a whole lot of other stuff.... How this plane got certified god only knows (though others have suggested the possible reason).....
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Why were the previous 3 flights recoverable but not this one ?
And with all the planes out there flying hundreds if not thousands of flights daily fitted with the same systems, why was this plane so far the only one exhibiting the anomaly ?
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Also as an engineer , with only 2 AoAs, I’d be reluctant to make any decision based on a disagree. Perhaps a “large” disagree, but in any case, without a majority vote, asking HAL for nose-down Trim seems scary.
The AD states AoA disagree plus (in concert with) other “faults”. The key problem is that appropriate data that should have been in the Manual was missing.
One of these faults is “unable to disengage autopilot”. Which is interesting, because the mystery problem occurs only in manual flight.
in any case, the AD refers to “erroneous” AoA data. As two discrete installed systems, Independence of data sources instead of sampled together, seems an odd approach.
It may be Boeing’s idea to keep them discrete so a simple change of command would likely solve the MCAS issue. However, handing off a corrupted flight path might be worse.
One of these faults is “unable to disengage autopilot”. Which is interesting, because the mystery problem occurs only in manual flight.
in any case, the AD refers to “erroneous” AoA data. As two discrete installed systems, Independence of data sources instead of sampled together, seems an odd approach.
It may be Boeing’s idea to keep them discrete so a simple change of command would likely solve the MCAS issue. However, handing off a corrupted flight path might be worse.
Last edited by Concours77; 11th Nov 2018 at 14:59.
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RE: That allied pilot's link
Another leaked document? Dayum.
Last edited by SLFstu; 11th Nov 2018 at 14:51. Reason: added Smott999's original title
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The Emergency Airworthiness Directive is available on the FAA's website. The APA letter posted by Halfnut contains a link to that Airworthiness Directive.
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posted on November 10, 2018 09:22
At the heart of this investigation is the MCAS system (description from Boeing):
MCAS (Maneuvering Characteristics Augmentation System) is implemented on the 737 MAX to enhance pitch characteristics with flaps UP and at elevated angles of attack. The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors and during flaps up flight at airspeeds approaching stall. MCAS is activated without pilot input and only operates in manual, flaps up flight. The system is designed to allow the flight crew to use column trim switch or stabilizer aislestand cutout switches to override MCAS input. The function is commanded by the Flight Control computer using input data from sensors and other airplane systems.
The MCAS function becomes active when the airplane Angle of Attack exceeds a threshold based on airspeed and altitude. Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers. The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.
This is the first description you, as 737 pilots, have seen. It is not in the AA 737 Flight Manual Part 2, nor is there a description in the Boeing FCOM. It will be soon.
Captain XXXXXXX
DFW 737I
APA Safety Committee Chairman
737 MAX8 Emergency Airworthiness Directive
posted on November 10, 2018 09:22
737 MAX8 Emergency Airworthiness Directive
The recently released Emergency Airworthiness Directive directs pilots how to deal with a known issue, but it does nothing to address the systems issues with the AOA system, which may be the causal system in the Lion Air accident. This is significant. The positive takeaway is that we are advised, as pilots, that once we recognize the issue, we can stop the negative impacts by taking the trim system out of the loop.At the heart of this investigation is the MCAS system (description from Boeing):
MCAS (Maneuvering Characteristics Augmentation System) is implemented on the 737 MAX to enhance pitch characteristics with flaps UP and at elevated angles of attack. The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors and during flaps up flight at airspeeds approaching stall. MCAS is activated without pilot input and only operates in manual, flaps up flight. The system is designed to allow the flight crew to use column trim switch or stabilizer aislestand cutout switches to override MCAS input. The function is commanded by the Flight Control computer using input data from sensors and other airplane systems.
The MCAS function becomes active when the airplane Angle of Attack exceeds a threshold based on airspeed and altitude. Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers. The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.
This is the first description you, as 737 pilots, have seen. It is not in the AA 737 Flight Manual Part 2, nor is there a description in the Boeing FCOM. It will be soon.
Captain XXXXXXX
DFW 737I
APA Safety Committee Chairman
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Reading the letter pasted by Halfnut above my understanding is:
1. ) The Maneuvering Characteristics Augmentation System (MCAS) is a system that is distinct from the Speed Trim System (STS) and not merely an alternate name for the STS.
2.) The 737 MAX has a system whcih makes significant adjustments to the flight control system, whcih change the way the airplane flies, and Boeing provided no information on this system in operating manuals or related literature (at least to flight operations departments) .
Is this incorrect or inaccurate?
1. ) The Maneuvering Characteristics Augmentation System (MCAS) is a system that is distinct from the Speed Trim System (STS) and not merely an alternate name for the STS.
2.) The 737 MAX has a system whcih makes significant adjustments to the flight control system, whcih change the way the airplane flies, and Boeing provided no information on this system in operating manuals or related literature (at least to flight operations departments) .
Is this incorrect or inaccurate?
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