Moderators: jsumali2, richierich, ua900, PanAm_DC10, hOMSaR
smartplane wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
Certification loophole. Optional extras are discounted from grandfathering formula. If standard, questions would be asked why, whats changed from earlier models.....................
WIederling wrote:smartplane wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
Certification loophole. Optional extras are discounted from grandfathering formula. If standard, questions would be asked why, whats changed from earlier models.....................
Interesting to know. ( who ordered the option and did they get a hint to better order that too ? )
RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
RickNRoll wrote:
WIederling wrote:RickNRoll wrote:
that the same outfit that moved MCAS to pilot training?
If yes how did they get the intelligence?
reading Ostrower: they ordered that option after the Lion Air crash. ( end of November 2018 )
but I seem to remember that one US airline had the MCAS info from the getgo.
who was it?
SteinarN wrote:Brazilian aothorities demanded Boeing put the MCAS description in the manuals for the pilots. So pilots in any Brazilian airlines would at least have access to that basic MCAS description making them avare of its existence at least.
Regarding optional AoA display and disagree messages. If grandfathering clauses forced Boeing to make those cocpit messages and displays optional and Boeing really felt they should have been there to help the pilots, then why did Boeing charge something like 100.000 US$ for that option? Instead of offer them for say one or ten US$?
The answer is obviously that Boeing wished to keep that system under the radar of the pilots for whatever reason.
WIederling wrote:RickNRoll wrote:
that the same outfit that moved MCAS to pilot training?
If yes how did they get the intelligence?
reading Ostrower: they ordered that option after the Lion Air crash. ( end of November 2018 )
but I seem to remember that one US airline had the MCAS info from the getgo.
who was it?
mandala499 wrote:With all this Max saga unfolding... why can't Boeing just come up with a temporary fix like:
1. Make AOA disagree warning mandatory
2. If "AOA DISAGREE" comes up after take off, do not retract flaps to UP, and land ASAP.
3. If "AOA DISAGREE" comes up at any other time, LAND ASAP, consider flights with flaps 1 or more.
Yes the above are overly simplified, and I believe while crude, would save lives, and save the Max... BUT, the downside is, such a procedure, might not save Boeing from a lot of liability lawsuits, because it admits a flaw in an explicit way...
dragon6172 wrote:smartplane wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
Certification loophole. Optional extras are discounted from grandfathering formula. If standard, questions would be asked why, whats changed from earlier models.....................
Are you trying to say these optional extras were not made standard to hide MCAS from certifying authority or operators?
hayzel777 wrote:WIederling wrote:RickNRoll wrote:
that the same outfit that moved MCAS to pilot training?
If yes how did they get the intelligence?
reading Ostrower: they ordered that option after the Lion Air crash. ( end of November 2018 )
but I seem to remember that one US airline had the MCAS info from the getgo.
who was it?
I believe it was AA.
EDIT: https://viewfromthewing.boardingarea.co ... know-more/
APA says AA was the only one to have one indicator for each pilot from the get go.
LDRA wrote:mandala499 wrote:With all this Max saga unfolding... why can't Boeing just come up with a temporary fix like:
1. Make AOA disagree warning mandatory
2. If "AOA DISAGREE" comes up after take off, do not retract flaps to UP, and land ASAP.
3. If "AOA DISAGREE" comes up at any other time, LAND ASAP, consider flights with flaps 1 or more.
Yes the above are overly simplified, and I believe while crude, would save lives, and save the Max... BUT, the downside is, such a procedure, might not save Boeing from a lot of liability lawsuits, because it admits a flaw in an explicit way...
Current AOA DISAGREE logic fault threshold is 10deg difference between two sensors. That tolerance threshold may be too wide to completely prevent false activation of MCAS, especially under low speed high grossweight condition(actual AoA on the high side). I believe MCAS activation is around ~15deg AoA? So if aircraft is flying around with 5degree actual AoA, current AOA DISAGREE logic would not trigger on false activation of MCAS
Also current AOA DISAGREE logic may not be certified to assurance level needed for flight control
LDRA wrote:Current AOA DISAGREE logic fault threshold is 10deg difference between two sensors. That tolerance threshold may be too wide to completely prevent false activation of MCAS, especially under low speed high grossweight condition(actual AoA on the high side). I believe MCAS activation is around ~15deg AoA? So if aircraft is flying around with 5degree actual AoA, current AOA DISAGREE logic would not trigger on false activation of MCAS
Also current AOA DISAGREE logic may not be certified to assurance level needed for flight control
zeke wrote:While there is only two physical AOA sensors, each sensor has two resolvers, the resolvers are basically the raw AOA values. In reality there is presently 4 AOA values which could be compared.
There could be a local comparison on the sensor as each resolver should agree with each other, if one resolver is saying 10 degrees and the other 2.5 degrees you know that physical AOA sensor is suspect as the two resolvers don’t closely agree.
zeke wrote:Great info. Thanks.While there is only two physical AOA sensors, each sensor has two resolvers, the resolvers are basically the raw AOA values. In reality there is presently 4 AOA values which could be compared.
There could be a local comparison on the sensor as each resolver should agree with each other, if one resolver is saying 10 degrees and the other 2.5 degrees you know that physical AOA sensor is suspect as the two resolvers don’t closely agree.
The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down. After the Lion Air Flight 610 crash, Boeing for the first time provided to airlines details about MCAS. Boeing’s bulletin to the airlines stated that the limit of MCAS’s command was 2.5 degrees.
That number was new to FAA engineers who had seen 0.6 degrees in the safety assessment. “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
PixelFlight wrote:https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/
Aside of the FAA safety assessment activity delegation to Boeing scandal, I found this regarding MCAS:The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down. After the Lion Air Flight 610 crash, Boeing for the first time provided to airlines details about MCAS. Boeing’s bulletin to the airlines stated that the limit of MCAS’s command was 2.5 degrees.
That number was new to FAA engineers who had seen 0.6 degrees in the safety assessment. “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
This real 2.5 degree versus 0.6 degree in the certification could be part of the explanation why Boeing didn't document the MCAS before.
VS11 wrote:PixelFlight wrote:https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/
Aside of the FAA safety assessment activity delegation to Boeing scandal, I found this regarding MCAS:The original Boeing document provided to the FAA included a description specifying a limit to how much the system could move the horizontal tail — a limit of 0.6 degrees, out of a physical maximum of just less than 5 degrees of nose-down movement. That limit was later increased after flight tests showed that a more powerful movement of the tail was required to avert a high-speed stall, when the plane is in danger of losing lift and spiraling down. After the Lion Air Flight 610 crash, Boeing for the first time provided to airlines details about MCAS. Boeing’s bulletin to the airlines stated that the limit of MCAS’s command was 2.5 degrees.
That number was new to FAA engineers who had seen 0.6 degrees in the safety assessment. “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
This real 2.5 degree versus 0.6 degree in the certification could be part of the explanation why Boeing didn't document the MCAS before.
In addition, MCAS engaged on both sides even though the AOA was faulty on the left side. From the Seattle Times article:
"The black box data released in the preliminary investigation report shows that after this cycle repeated 21 times, the plane’s captain ceded control to the first officer. As MCAS pushed the nose down two or three times more, the first officer responded with only two short flicks of the thumb switches."
Why did MCAS engage while the FO was flying the plane? If his AOA indicator was functioning properly, MCAS should not have engaged. People expressing concern with the air data computers may have a point. It could be more than just MCAS.
Finn350 wrote:VS11 wrote:PixelFlight wrote:https://www.seattletimes.com/business/boeing-aerospace/failed-certification-faa-missed-safety-issues-in-the-737-max-system-implicated-in-the-lion-air-crash/
Aside of the FAA safety assessment activity delegation to Boeing scandal, I found this regarding MCAS:
This real 2.5 degree versus 0.6 degree in the certification could be part of the explanation why Boeing didn't document the MCAS before.
In addition, MCAS engaged on both sides even though the AOA was faulty on the left side. From the Seattle Times article:
"The black box data released in the preliminary investigation report shows that after this cycle repeated 21 times, the plane’s captain ceded control to the first officer. As MCAS pushed the nose down two or three times more, the first officer responded with only two short flicks of the thumb switches."
Why did MCAS engage while the FO was flying the plane? If his AOA indicator was functioning properly, MCAS should not have engaged. People expressing concern with the air data computers may have a point. It could be more than just MCAS.
There is a single MCAS implementation, not separate for the Captain and the FO. It doesn't matter who flies the plane, during any single flight the MCAS used only one of the two AoA sensors as input.
VS11 wrote:Finn350 wrote:VS11 wrote:
In addition, MCAS engaged on both sides even though the AOA was faulty on the left side. From the Seattle Times article:
"The black box data released in the preliminary investigation report shows that after this cycle repeated 21 times, the plane’s captain ceded control to the first officer. As MCAS pushed the nose down two or three times more, the first officer responded with only two short flicks of the thumb switches."
Why did MCAS engage while the FO was flying the plane? If his AOA indicator was functioning properly, MCAS should not have engaged. People expressing concern with the air data computers may have a point. It could be more than just MCAS.
There is a single MCAS implementation, not separate for the Captain and the FO. It doesn't matter who flies the plane, during any single flight the MCAS used only one of the two AoA sensors as input.
In previous articles it was explained that M.C.A.S. was using the AOA from the side that is flying the aircraft. So when FO took over, M.C.A.S. would have used the right side AOA.
Finn350 wrote:VS11 wrote:Finn350 wrote:
There is a single MCAS implementation, not separate for the Captain and the FO. It doesn't matter who flies the plane, during any single flight the MCAS used only one of the two AoA sensors as input.
In previous articles it was explained that M.C.A.S. was using the AOA from the side that is flying the aircraft. So when FO took over, M.C.A.S. would have used the right side AOA.
You have misunderstood it.
SheikhDjibouti wrote:Finn350 wrote:VS11 wrote:
In previous articles it was explained that M.C.A.S. was using the AOA from the side that is flying the aircraft. So when FO took over, M.C.A.S. would have used the right side AOA.
You have misunderstood it.
In that case you can add me to the list; I must have "misunderstood" it too.
I just wish I could find the relevant posts upthread; I'm not certain what search criteria is needed to narrow it down from over 6000 posts
VS11 wrote:Here is the passage:
"In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from only one of the two angle of attack sensors at a time, depending on which of two, redundant flight control computers — one on the captain’s side, one on the first officer’s side — happened to be active on that flight."
Can the active side switch mid-flight? If yes, then I most certainly did not misunderstand. If no, then I sure did and thanks for clarifying. It does make a difference.
VS11 wrote:SheikhDjibouti wrote:Finn350 wrote:
You have misunderstood it.
In that case you can add me to the list; I must have "misunderstood" it too.
I just wish I could find the relevant posts upthread; I'm not certain what search criteria is needed to narrow it down from over 6000 posts
It was in the thread about the NYT article (https://www.nytimes.com/2019/02/03/worl ... ilots.html) :
https://www.airliners.net/forum/viewtop ... #p21067105
Here is the passage:
"In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from only one of the two angle of attack sensors at a time, depending on which of two, redundant flight control computers — one on the captain’s side, one on the first officer’s side — happened to be active on that flight."
Can the active side switch mid-flight? If yes, then I most certainly did not misunderstand. If no, then I sure did and thanks for clarifying. It does make a difference.
mandala499 wrote:Just a guess...
Finn350 wrote:VS11 wrote:SheikhDjibouti wrote:In that case you can add me to the list; I must have "misunderstood" it too.
I just wish I could find the relevant posts upthread; I'm not certain what search criteria is needed to narrow it down from over 6000 posts
It was in the thread about the NYT article (https://www.nytimes.com/2019/02/03/worl ... ilots.html) :
viewtopic.php?f=3&t=1414709&p=21067105#p21067105
Here is the passage:
"In designing the 737 Max, Boeing decided to feed M.C.A.S. with data from only one of the two angle of attack sensors at a time, depending on which of two, redundant flight control computers — one on the captain’s side, one on the first officer’s side — happened to be active on that flight."
Can the active side switch mid-flight? If yes, then I most certainly did not misunderstand. If no, then I sure did and thanks for clarifying. It does make a difference.
This is the best quote I could find: MCAS is implemented within the two Flight Control Computers (FCCs). The Left FCC uses the Left AOA sensor for MCAS and the Right FCC uses the Right AOA sensor for MCAS. Only one FCC operates at a time to provide MCAS commands. With electrical power to the FCCs maintained, the unit that provides MCAS changes between flights. In this manner, the AOA sensor that is used for MCAS changes with each flight.
http://www.b737.org.uk/mcas.htm
WIederling wrote:
is that two independent resolvers working on the same vane or just a twinned output driver?
( how do they accomodate the left right swap? swap resolvers too, with one resolver handing out the complement of the other ersolver?)
zeke wrote:WIederling wrote:
is that two independent resolvers working on the same vane or just a twinned output driver?
( how do they accomodate the left right swap? swap resolvers too, with one resolver handing out the complement of the other ersolver?)
My understanding it is a single AOA probe has two resolvers on the one vane. A resolver is a form of sensor that relies on inductive coupling to two orthogonal pickups (SIN and COS). The outputs of the resolver are modulated by a reference carrier. Their output amplitudes relate to the shaft angle. The aircraft also has two Stall Management Yaw Dampers (SMYD), and two Flight Control Computers (FCC).
I understand the one of the outputs of the resolver go to same side SYMD, and the other to the opposite side FCC.
DDR wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
For the love of God, why would it be optional?
klkla wrote:DDR wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
PixelFlight wrote:
It look like none of the FCC has AoA input. Instead each ADIRU have an AoA input. Each FCC use both ADIRU. So the FCC can use both AoA values (from the two ADIRUs).
What's strange is that both SYMDs are feed by the two ADIRUs too, but for some unexplained reason, without the AoA values. Each SYMD use a dedicated SIN/COS link from a single sensor to get that AoA value. That part puzzle me...
zeke wrote:PixelFlight wrote:
It look like none of the FCC has AoA input. Instead each ADIRU have an AoA input. Each FCC use both ADIRU. So the FCC can use both AoA values (from the two ADIRUs).
What's strange is that both SYMDs are feed by the two ADIRUs too, but for some unexplained reason, without the AoA values. Each SYMD use a dedicated SIN/COS link from a single sensor to get that AoA value. That part puzzle me...
This was posted earlier in this thread by fadecfault, it shows an AOA input to the FCC.
klkla wrote:DDR wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
mxaxai wrote:klkla wrote:DDR wrote:
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
Because it's declared optional, hence obviously not safety critical, and costs money?
An airline has to rely on the manufacturer and the certifying agency that the aircraft is, in principle, safe as sold.
mxaxai wrote:klkla wrote:DDR wrote:
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
Because it's declared optional, hence obviously not safety critical, and costs money?
An airline has to rely on the manufacturer and the certifying agency that the aircraft is, in principle, safe as sold.
klkla wrote:DDR wrote:RickNRoll wrote:There is a warning system on the 737Max that warns if the AoA sensors disagree. It's an Optional Extra.
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
DDR wrote:klkla wrote:DDR wrote:
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
Amen! Great post!!
edu2703 wrote:From Bloomberg:
BREAKING: An off-duty pilot who happened to be riding in the cockpit saved a diving Boeing 737 Max 8. The next day, the same Lion Air jet crashed into the Java Sea, killing all 189 aboard
https://www.bloomberg.com/news/articles ... er-crashed
“They didn’t seem to know the trim was moving down,” the third source said. “They thought only about airspeed and altitude. That was the only thing they talked about.”
DDR wrote:klkla wrote:DDR wrote:
For the love of God, why would it be optional?
Also, for the love of god, why would any airline NOT order it?
Amen! Great post!!
