How difficult is it to simply disable/disengage the MCAS on Boeing 737 Max 8 & 9 Aircraft?Can computer imposed inputs be overridden on the Boeing 737-MAX?Does the Boeing 737 MAX use electro-hydraulic actuators?How long is the horizontal stabilizer on a Boeing 737?Is there any difference between the Boeing 787 and the 737 MAX?What is the maximum take off climb angle of a Boeing 737 MAX?Why is the 737 MAX 7 selling so poorly?How safe is the Boeing 737-800 in high winds?How unusual is the 737 MAX 8's crash history?Is the 737-900 safer than the 737 Max?Where are the grounded 737 Max planes being kept?Why is Germany not able to read data from the Boeing 737 MAX black boxes?
How to read the value of this capacitor?
Interplanetary conflict, some disease destroys the ability to understand or appreciate music
Official degrees of earth’s rotation per day
What approach do we need to follow for projects without a test environment?
PTIJ: Who should I vote for? (21st Knesset Edition)
Why do Australian milk farmers need to protest supermarkets' milk price?
Do I need life insurance if I can cover my own funeral costs?
Should we release the security issues we found in our product as CVE or we can just update those on weekly release notes?
Is there a data structure that only stores hash codes and not the actual objects?
What exactly is this small puffer fish doing and how did it manage to accomplish such a feat?
Define, (actually define) the "stability" and "energy" of a compound
How do I hide Chekhov's Gun?
Does Wild Magic Surge trigger off of spells on the Sorcerer spell list, if I learned them from another class?
Why do passenger jet manufacturers design their planes with stall prevention systems?
Are there verbs that are neither telic, or atelic?
Why is the President allowed to veto a cancellation of emergency powers?
SOQL: Populate a Literal List in WHERE IN Clause
Error in Twin Prime Conjecture
Min function accepting varying number of arguments in C++17
Combining an idiom with a metonymy
Sailing the cryptic seas
How do anti-virus programs start at Windows boot?
How difficult is it to simply disable/disengage the MCAS on Boeing 737 Max 8 & 9 Aircraft?
What is a^b and (a&b)<<1?
How difficult is it to simply disable/disengage the MCAS on Boeing 737 Max 8 & 9 Aircraft?
Can computer imposed inputs be overridden on the Boeing 737-MAX?Does the Boeing 737 MAX use electro-hydraulic actuators?How long is the horizontal stabilizer on a Boeing 737?Is there any difference between the Boeing 787 and the 737 MAX?What is the maximum take off climb angle of a Boeing 737 MAX?Why is the 737 MAX 7 selling so poorly?How safe is the Boeing 737-800 in high winds?How unusual is the 737 MAX 8's crash history?Is the 737-900 safer than the 737 Max?Where are the grounded 737 Max planes being kept?Why is Germany not able to read data from the Boeing 737 MAX black boxes?
$begingroup$
With regard to the Ethiopian crash of the 737 Max 8 aircraft, where according to preliminary reports, it appears to be related to the MCAS which is a safety system that pushes the nose down in the even of an excessively high angle of attack (pitch attitude), how difficult is it for the pilots to simply disable the MCAS and manually fly the plane?
To clarify my question, what I'm asking is can the pilot disengage the MCAS and if so, how do they do that? Is it just flipping a switch or popping a breaker, or is it a complicated set of procedures?
safety aircraft-systems boeing-737 mcas
asked 11 hours ago
Devil07Devil07
5,6631554
$endgroup$
add a comment |
$begingroup$
With regard to the Ethiopian crash of the 737 Max 8 aircraft, where according to preliminary reports, it appears to be related to the MCAS which is a safety system that pushes the nose down in the even of an excessively high angle of attack (pitch attitude), how difficult is it for the pilots to simply disable the MCAS and manually fly the plane?
To clarify my question, what I'm asking is can the pilot disengage the MCAS and if so, how do they do that? Is it just flipping a switch or popping a breaker, or is it a complicated set of procedures?
safety aircraft-systems boeing-737 mcas
asked 11 hours ago
Devil07Devil07
5,6631554
$endgroup$
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
3
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
1
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago
add a comment |
$begingroup$
With regard to the Ethiopian crash of the 737 Max 8 aircraft, where according to preliminary reports, it appears to be related to the MCAS which is a safety system that pushes the nose down in the even of an excessively high angle of attack (pitch attitude), how difficult is it for the pilots to simply disable the MCAS and manually fly the plane?
To clarify my question, what I'm asking is can the pilot disengage the MCAS and if so, how do they do that? Is it just flipping a switch or popping a breaker, or is it a complicated set of procedures?
safety aircraft-systems boeing-737 mcas
asked 11 hours ago
Devil07Devil07
5,6631554
$endgroup$
With regard to the Ethiopian crash of the 737 Max 8 aircraft, where according to preliminary reports, it appears to be related to the MCAS which is a safety system that pushes the nose down in the even of an excessively high angle of attack (pitch attitude), how difficult is it for the pilots to simply disable the MCAS and manually fly the plane?
To clarify my question, what I'm asking is can the pilot disengage the MCAS and if so, how do they do that? Is it just flipping a switch or popping a breaker, or is it a complicated set of procedures?
safety aircraft-systems boeing-737 mcas
safety aircraft-systems boeing-737 mcas
asked 11 hours ago
Devil07Devil07
5,6631554
asked 11 hours ago
Devil07Devil07
5,6631554
edited 9 hours ago
Devil07
asked 11 hours ago
Devil07Devil07
5,6631554
asked 11 hours ago
Devil07Devil07
5,6631554
asked 11 hours ago
Devil07Devil07
5,6631554
5,6631554
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
3
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
1
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago
add a comment |
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
3
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
1
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
3
3
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
1
1
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago
add a comment |
2 Answers
2
active
oldest
votes
$begingroup$
MCAS doesn't have its own on/off switch
It is a fly by wire feature designed to account for a particular flight regime that would not (or was not expected to) be encountered very often in normal operations. The system was adapted to account for some of the aerodynamics of the engine installation for this model. Its activation requires a number of preconditions, but we'll get to that in a moment.
A few things that should disable it (with caveats)
Lower the flaps. It is intended to work only if the flaps are up.
Turn the Stab Trim switches to OFF. This disables the horizontal stabilizer's trim completely, and revert to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). This means that the pilots will manipulate
the trim wheels in order to apply nose/pitch trim during flight.
This approach appears to be what a few crews did prior to the LionAir crash in October 2018 when the system gave them problems. (It is unclear how many of the crews knew that is was MCAS, versus any other trim anomaly). The previous LionAir crews on the accident aircraft ended up having to fly to their destination manually. Original Source: the Preliminary Report from that accident.
The report indicates that during several previous flights of the 737 involved in the Lion Air crash, pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off. The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. The problems with the Jakarta flight were recorded in the aircraft’s maintenance log. However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)
Enable autopilot. It is supposed to only work if the autopilot is off. But...CAVEAT
That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system which is run by the FCCs - keeps getting spurious signals from the AoA sensors. (Or if the pitot static system is providing bad data to the FCCs).
How do you know that you need to disable MCAS?
The problem for a given crew: how do you know that MCAS is the sub-system that is giving you trouble? The AD released in December of 2018 updated the Runaway Stabilizer procedure; since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same symptom may manifest during differently caused malfunctions. (See the example above). If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, is an issue that gets to the heart of
What is in the pilots manuals
What training the crews do, or do not, get on this sub system.
The sub system is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off. This includes high angle of bank flight in such conditions.
CAVEAT
Take a look at that last bullet in the lower right of the figure. It's only partially correct. When the pilots override with manual trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition goes away.
"In the event of erroneous AOA data, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds,"
Boeing explained to operators in a bulletin issued last November,
following the JT610 accident. "The nose down stabilizer trim movement
can be stopped and reversed with the use of the electric stabilizer
trim switches but may restart 5 sec. after the electric stabilizer
trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is
deactivated." (source)
It is this behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash. They were airborne for about six minutes before they were no longer able to overcome the horizontal stab position with their trim controls. (Caveat: current as of early 2019. When the final report comes out this may become a lot clearer).
Why is this activating during takeoff/departure?
That MCAS appears to activate during routine flight regimes is what is believed to be catching some crews by surprise - and not just the two accident crews. There is a recent article in Atlantic that excerpts some NASA reports by aircrews in the US about odd nose/pitch behavior in this model aircraft.
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
$endgroup$
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
|
show 1 more comment
$begingroup$
You can disable the stabaliser trim which will prevent MCAS from making inputs to the aircraft.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
return StackExchange.using("mathjaxEditing", function ()
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix)
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
);
);
, "mathjax-editing");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "528"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2faviation.stackexchange.com%2fquestions%2f61203%2fhow-difficult-is-it-to-simply-disable-disengage-the-mcas-on-boeing-737-max-8-9%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
MCAS doesn't have its own on/off switch
It is a fly by wire feature designed to account for a particular flight regime that would not (or was not expected to) be encountered very often in normal operations. The system was adapted to account for some of the aerodynamics of the engine installation for this model. Its activation requires a number of preconditions, but we'll get to that in a moment.
A few things that should disable it (with caveats)
Lower the flaps. It is intended to work only if the flaps are up.
Turn the Stab Trim switches to OFF. This disables the horizontal stabilizer's trim completely, and revert to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). This means that the pilots will manipulate
the trim wheels in order to apply nose/pitch trim during flight.This approach appears to be what a few crews did prior to the LionAir crash in October 2018 when the system gave them problems. (It is unclear how many of the crews knew that is was MCAS, versus any other trim anomaly). The previous LionAir crews on the accident aircraft ended up having to fly to their destination manually. Original Source: the Preliminary Report from that accident.
The report indicates that during several previous flights of the 737 involved in the Lion Air crash, pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off. The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. The problems with the Jakarta flight were recorded in the aircraft’s maintenance log. However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)
Enable autopilot. It is supposed to only work if the autopilot is off. But...CAVEAT
That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system which is run by the FCCs - keeps getting spurious signals from the AoA sensors. (Or if the pitot static system is providing bad data to the FCCs).
How do you know that you need to disable MCAS?
The problem for a given crew: how do you know that MCAS is the sub-system that is giving you trouble? The AD released in December of 2018 updated the Runaway Stabilizer procedure; since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same symptom may manifest during differently caused malfunctions. (See the example above). If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, is an issue that gets to the heart of
What is in the pilots manuals
What training the crews do, or do not, get on this sub system.
The sub system is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off. This includes high angle of bank flight in such conditions.
CAVEAT
Take a look at that last bullet in the lower right of the figure. It's only partially correct. When the pilots override with manual trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition goes away.
"In the event of erroneous AOA data, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds,"
Boeing explained to operators in a bulletin issued last November,
following the JT610 accident. "The nose down stabilizer trim movement
can be stopped and reversed with the use of the electric stabilizer
trim switches but may restart 5 sec. after the electric stabilizer
trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is
deactivated." (source)
It is this behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash. They were airborne for about six minutes before they were no longer able to overcome the horizontal stab position with their trim controls. (Caveat: current as of early 2019. When the final report comes out this may become a lot clearer).
Why is this activating during takeoff/departure?
That MCAS appears to activate during routine flight regimes is what is believed to be catching some crews by surprise - and not just the two accident crews. There is a recent article in Atlantic that excerpts some NASA reports by aircrews in the US about odd nose/pitch behavior in this model aircraft.
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
$endgroup$
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
|
show 1 more comment
$begingroup$
MCAS doesn't have its own on/off switch
It is a fly by wire feature designed to account for a particular flight regime that would not (or was not expected to) be encountered very often in normal operations. The system was adapted to account for some of the aerodynamics of the engine installation for this model. Its activation requires a number of preconditions, but we'll get to that in a moment.
A few things that should disable it (with caveats)
Lower the flaps. It is intended to work only if the flaps are up.
Turn the Stab Trim switches to OFF. This disables the horizontal stabilizer's trim completely, and revert to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). This means that the pilots will manipulate
the trim wheels in order to apply nose/pitch trim during flight.This approach appears to be what a few crews did prior to the LionAir crash in October 2018 when the system gave them problems. (It is unclear how many of the crews knew that is was MCAS, versus any other trim anomaly). The previous LionAir crews on the accident aircraft ended up having to fly to their destination manually. Original Source: the Preliminary Report from that accident.
The report indicates that during several previous flights of the 737 involved in the Lion Air crash, pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off. The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. The problems with the Jakarta flight were recorded in the aircraft’s maintenance log. However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)
Enable autopilot. It is supposed to only work if the autopilot is off. But...CAVEAT
That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system which is run by the FCCs - keeps getting spurious signals from the AoA sensors. (Or if the pitot static system is providing bad data to the FCCs).
How do you know that you need to disable MCAS?
The problem for a given crew: how do you know that MCAS is the sub-system that is giving you trouble? The AD released in December of 2018 updated the Runaway Stabilizer procedure; since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same symptom may manifest during differently caused malfunctions. (See the example above). If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, is an issue that gets to the heart of
What is in the pilots manuals
What training the crews do, or do not, get on this sub system.
The sub system is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off. This includes high angle of bank flight in such conditions.
CAVEAT
Take a look at that last bullet in the lower right of the figure. It's only partially correct. When the pilots override with manual trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition goes away.
"In the event of erroneous AOA data, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds,"
Boeing explained to operators in a bulletin issued last November,
following the JT610 accident. "The nose down stabilizer trim movement
can be stopped and reversed with the use of the electric stabilizer
trim switches but may restart 5 sec. after the electric stabilizer
trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is
deactivated." (source)
It is this behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash. They were airborne for about six minutes before they were no longer able to overcome the horizontal stab position with their trim controls. (Caveat: current as of early 2019. When the final report comes out this may become a lot clearer).
Why is this activating during takeoff/departure?
That MCAS appears to activate during routine flight regimes is what is believed to be catching some crews by surprise - and not just the two accident crews. There is a recent article in Atlantic that excerpts some NASA reports by aircrews in the US about odd nose/pitch behavior in this model aircraft.
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
$endgroup$
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
|
show 1 more comment
$begingroup$
MCAS doesn't have its own on/off switch
It is a fly by wire feature designed to account for a particular flight regime that would not (or was not expected to) be encountered very often in normal operations. The system was adapted to account for some of the aerodynamics of the engine installation for this model. Its activation requires a number of preconditions, but we'll get to that in a moment.
A few things that should disable it (with caveats)
Lower the flaps. It is intended to work only if the flaps are up.
Turn the Stab Trim switches to OFF. This disables the horizontal stabilizer's trim completely, and revert to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). This means that the pilots will manipulate
the trim wheels in order to apply nose/pitch trim during flight.This approach appears to be what a few crews did prior to the LionAir crash in October 2018 when the system gave them problems. (It is unclear how many of the crews knew that is was MCAS, versus any other trim anomaly). The previous LionAir crews on the accident aircraft ended up having to fly to their destination manually. Original Source: the Preliminary Report from that accident.
The report indicates that during several previous flights of the 737 involved in the Lion Air crash, pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off. The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. The problems with the Jakarta flight were recorded in the aircraft’s maintenance log. However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)
Enable autopilot. It is supposed to only work if the autopilot is off. But...CAVEAT
That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system which is run by the FCCs - keeps getting spurious signals from the AoA sensors. (Or if the pitot static system is providing bad data to the FCCs).
How do you know that you need to disable MCAS?
The problem for a given crew: how do you know that MCAS is the sub-system that is giving you trouble? The AD released in December of 2018 updated the Runaway Stabilizer procedure; since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same symptom may manifest during differently caused malfunctions. (See the example above). If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, is an issue that gets to the heart of
What is in the pilots manuals
What training the crews do, or do not, get on this sub system.
The sub system is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off. This includes high angle of bank flight in such conditions.
CAVEAT
Take a look at that last bullet in the lower right of the figure. It's only partially correct. When the pilots override with manual trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition goes away.
"In the event of erroneous AOA data, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds,"
Boeing explained to operators in a bulletin issued last November,
following the JT610 accident. "The nose down stabilizer trim movement
can be stopped and reversed with the use of the electric stabilizer
trim switches but may restart 5 sec. after the electric stabilizer
trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is
deactivated." (source)
It is this behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash. They were airborne for about six minutes before they were no longer able to overcome the horizontal stab position with their trim controls. (Caveat: current as of early 2019. When the final report comes out this may become a lot clearer).
Why is this activating during takeoff/departure?
That MCAS appears to activate during routine flight regimes is what is believed to be catching some crews by surprise - and not just the two accident crews. There is a recent article in Atlantic that excerpts some NASA reports by aircrews in the US about odd nose/pitch behavior in this model aircraft.
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
$endgroup$
MCAS doesn't have its own on/off switch
It is a fly by wire feature designed to account for a particular flight regime that would not (or was not expected to) be encountered very often in normal operations. The system was adapted to account for some of the aerodynamics of the engine installation for this model. Its activation requires a number of preconditions, but we'll get to that in a moment.
A few things that should disable it (with caveats)
Lower the flaps. It is intended to work only if the flaps are up.
Turn the Stab Trim switches to OFF. This disables the horizontal stabilizer's trim completely, and revert to manual trim (there are two guarded stabilizer trim switches in the aisle stand, see Windshear's answer). This means that the pilots will manipulate
the trim wheels in order to apply nose/pitch trim during flight.This approach appears to be what a few crews did prior to the LionAir crash in October 2018 when the system gave them problems. (It is unclear how many of the crews knew that is was MCAS, versus any other trim anomaly). The previous LionAir crews on the accident aircraft ended up having to fly to their destination manually. Original Source: the Preliminary Report from that accident.
The report indicates that during several previous flights of the 737 involved in the Lion Air crash, pilots encountered problems involving the AoA as well as the pitot tube used to measure airspeed. In a flight in the same plane the day before, to Jakarta, the pilot experienced many of the same symptoms as the pilots on flight JT610: the stick shaker activated during rotation, an indicated airspeed warning alert appeared, and the aircraft began automatically pushing the aircraft nose down.
The pilot, after determining that his flight display system was malfunctioning, ran a runaway stabilizer non-normal checklist which led to the MCAS being disconnected when the stabilizer trim switches were turned off. The copilot flew the rest of the flight using manual controls and without autopilot.
That Jakarta flight was using an angle of attack sensor that had been replaced after the previous Lion Air flight to Denpasar experienced problems. The problems with the Jakarta flight were recorded in the aircraft’s maintenance log. However, it is not clear whether the pilot communicated that he ran a runaway stabilizer non-normal checklist during the flight, which might have alerted the airline’s engineering staff that there was still a problem. (source)
Enable autopilot. It is supposed to only work if the autopilot is off. But...CAVEAT
That last part is a little bit complicated: the autopilot may not stay on if it - the autopilot system which is run by the FCCs - keeps getting spurious signals from the AoA sensors. (Or if the pitot static system is providing bad data to the FCCs).
How do you know that you need to disable MCAS?
The problem for a given crew: how do you know that MCAS is the sub-system that is giving you trouble? The AD released in December of 2018 updated the Runaway Stabilizer procedure; since there are other malfunctions possible in the trim system for pitch, such as a trim runaway, the same symptom may manifest during differently caused malfunctions. (See the example above). If additional symptoms are present, such as a stick shaker activating from an erroneous AoA indication, which problem do you solve first?
Which problem are you having?
Are you having both problems, or even something else?
That concern, the relationship between different potential failure modes, is an issue that gets to the heart of
What is in the pilots manuals
What training the crews do, or do not, get on this sub system.
The sub system is only supposed to activate under certain conditions (in theory): high angle-of-attack, flaps-up, flight with autopilot off. This includes high angle of bank flight in such conditions.
CAVEAT
Take a look at that last bullet in the lower right of the figure. It's only partially correct. When the pilots override with manual trim, MCAS will try again five seconds later (after the pilot has stopped) unless the triggering condition goes away.
"In the event of erroneous AOA data, the pitch trim system can trim
the stabilizer nose down in increments lasting up to 10 seconds,"
Boeing explained to operators in a bulletin issued last November,
following the JT610 accident. "The nose down stabilizer trim movement
can be stopped and reversed with the use of the electric stabilizer
trim switches but may restart 5 sec. after the electric stabilizer
trim switches are released. Repetitive cycles of uncommanded nose down
stabilizer continue to occur unless the stabilizer trim system is
deactivated." (source)
It is this behavior that is believed to have ultimately overcome the best efforts of the pilots in the LionAir crash. They were airborne for about six minutes before they were no longer able to overcome the horizontal stab position with their trim controls. (Caveat: current as of early 2019. When the final report comes out this may become a lot clearer).
Why is this activating during takeoff/departure?
That MCAS appears to activate during routine flight regimes is what is believed to be catching some crews by surprise - and not just the two accident crews. There is a recent article in Atlantic that excerpts some NASA reports by aircrews in the US about odd nose/pitch behavior in this model aircraft.
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
edited 2 hours ago
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
answered 10 hours ago
KorvinStarmastKorvinStarmast
2,9291228
2,9291228
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
|
show 1 more comment
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
is it fair to say that MCAS controls pitch through the automated Stab Trim system? So when MCAS is activated from a high AOA sensor reading, pilots will see Trim wheels spinning forward to reduce pitch?
$endgroup$
– Devil07
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 Which line are you getting that from? For that matter, what you just asked is its own question. suggest you ask it. I am addressing the diasabling of that feature. Whatever disables the trim beyond manual control is what disables the MCAS function. Apparently, trim over ride from the yoke does not. I've seen an explanation of the details ... give me a chance to find a link.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
@Devil07 FWIW, I have been watching the arguments about the stab trim system and this systems interaction for a few months, since Lion Air, and am leary of jumping into that briar patch.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
you're answer is great, I'm just trying to understand how it all works together. If MCAS causes aircraft to pitch nose down when it senses excessive AOA, then doesn't it do it through use of trim? If so, when MCAS is pitching nose down, won't the trim wheels physically turn by themselves? Your graphic says "MCAS moves horizontal stabilizer trim".
$endgroup$
– Devil07
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
$begingroup$
Not my graphic, @Devil07, TheAirCurrent's -- :) While I think you are right, I just need to recall which argument I was reading to link your thought to that. Give me a few. There is some interesting discussion on that here, based on the Lion Air accident. See if it's helpful to you. Beware, a few of the posters there are sharp, and a few are trolls.
$endgroup$
– KorvinStarmast
9 hours ago
|
show 1 more comment
$begingroup$
You can disable the stabaliser trim which will prevent MCAS from making inputs to the aircraft.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
add a comment |
$begingroup$
You can disable the stabaliser trim which will prevent MCAS from making inputs to the aircraft.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
add a comment |
$begingroup$
You can disable the stabaliser trim which will prevent MCAS from making inputs to the aircraft.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$endgroup$
You can disable the stabaliser trim which will prevent MCAS from making inputs to the aircraft.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 10 hours ago
WindshearWindshear
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
answered 10 hours ago
WindshearWindshear
411
answered 10 hours ago
WindshearWindshear
411
411
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Windshear is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
add a comment |
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
This is what I was thinking. If MCAS is pitching nose forward through use of stab trim, then the trim wheel will be visibly spinning forward (or will it?), if it is, then disable it and take manual control of trim.
$endgroup$
– Devil07
9 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
$begingroup$
Yes, the trim wheels will spin in case MCAS sends input. By disabling the stab trim, inputs to it by any system will be disabled.
$endgroup$
– Windshear
8 hours ago
add a comment |
Thanks for contributing an answer to Aviation Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2faviation.stackexchange.com%2fquestions%2f61203%2fhow-difficult-is-it-to-simply-disable-disengage-the-mcas-on-boeing-737-max-8-9%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
$begingroup$
Whether or not MCAS is the root cause of Ethiopian Crash is still unknown, though it is strongly suspected. It is suspected due to its relationship to the LionAir crash of October 2018, and what that investigation has uncovered. FWIW, most of what I understand about this system was triggered by that report and that incident and a variety of public releases, some good some bad, of information on that sub system. (And if they find that it's something else, or also something else, that may not be such good news for owners and operators).
$endgroup$
– KorvinStarmast
10 hours ago
3
$begingroup$
This question could be just as answerable without bringing up the two recent 737 Max crashes at all. You might consider just editing that part out; that would go a long way toward alleviating concerns that you want speculation on an accident, rather than operational details on an airplane.
$endgroup$
– a CVn
10 hours ago
1
$begingroup$
@aCVn I think context is important. Many people use this site, not all are aviation nerds, by providing context to the question it establishes why the question and answers, are relevant and important. At least, thats my opinion. :)
$endgroup$
– Devil07
9 hours ago
$begingroup$
Related: Can computer imposed inputs be overridden on the Boeing 737-MAX?
$endgroup$
– ymb1
8 hours ago