9 ms·

Internal FAA Review Saw High Risk of 737 Max Crashes

102 points by tompic823 7y ago

bookofjoe 7y ago
http://archive.is/JVWfg http://archive.is/JVWfg
- tpmx 7y ago
  Who keeps downvoting these archive.is comments and why? They are clearly very useful.
  - AnimalMuppet 7y ago
    They'd be a lot more useful with some hint about what's being linked to. A bare link, with an opaque URL, and with no comment, is basically saying "trust me, this points to something relevant, but I won't tell you what". If I disagree with the poster's definition of "relevant", I've wasted my time. How about telling me what you're linking to, not just giving me a raw, opaque link?
forgingahead 7y ago
The MAX’s safety record when it was grounded, after two years in service, roughly amounted to two catastrophic accidents for every one million flights, according to estimates by industry officials relying on unofficial data. By contrast, the model of 737 that came before the MAX has suffered one fatal crash for every 10 million flights, according to data from Boeing. Put another way, the 737 Max has a statistic of 1 catastrophe per 500k flights, whilst the 737 was 1 per 10 million, basically 20 times as much. This is criminal behaviour, and people need to go to jail. The MAX should never be allowed to fly again.
- jmpman 7y ago
  I could see justification for clawback on any stock awarded or exercised for the executives responsible for 737 Max problems, but I don’t see any evidence that the 737 Max is unredeemable.
  - addicted44 7y ago
    There likely appears to be only 1 way the Max can be redeemed, and that is for Boeing to accept it's a different enough plane that 737 pilots need new training for it.
    - deleted 7y ago
      [deleted]
    - caconym_ 7y ago
      Yes. Call it a new airplane, rip out the ridiculous and irresponsible hack that is the MCAS, and go from there.
  - beamatronic 7y ago
    It’s going to make a fantastic cargo plane
    - robmiller 7y ago
      Yup, I'm sure Amazon can get them at a discount for a Prime Air fleet.
    - joachim4 7y ago
      As a consumer there is no way I will never book a flight on a 737 Max (even if those planes are allowed to fly again), and if I have the choice between flying a Boeing and an Airbus, I will buy the flight on an Airbus. Boeing clearly needs to get back the flyers trust.
      - briandear 7y ago
        Is Airbus without problems?
  - adwi 7y ago
    It’s irredeemable on its name alone at this point.
- LeifCarrotson 7y ago
  On the other hand, generalizing from two incidents to a rate isn't great statistics. The list of accidents and incidents with the previous generation [1] shows some 9 fatal problems spread over more than a decade, which is closer to a rate. But saying that the 737 Max is known to be 20 times worse when the real value might be anywhere between 2 and 200 if it had been allowed to continue flying is a little imprecise. Put people in jail for negligence, sure. But we should be criminalizing based on that negligence and not on its results. [1]: https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Boeing_737#737_Next_Generation_(-600/-700/-800/-900)_aircraft https://en.wikipedia.org/wiki/List_of_accidents_and_incident...
  - ses1984 7y ago
    If it were just 2x worse wouldn't that still be pretty horrifying? Let's not split the wrong hairs.
    - tempguy9999 7y ago
      There are degrees of wrongness.
  - tpmx 7y ago
    In https://news.ycombinator.com/item?id=19437938 https://news.ycombinator.com/item?id=19437938 you wrote (8 months ago): The fault doesn't lie with the engineers who built the system...not to mention I would be very surprised if they were professionally certified. It lies with the managers who wrote the specification that said that for business reasons the new plane must not require any additional training or type certifications, and cut costs by implementing the required systems with a non-redundant sensor. (I agree.)
  - me_me_me 7y ago
    Agree overall, one thing to note is that 737 Max already capitalizes on all errors corrected from 737. Max is 20 worse with all off the old system being already excluded from possibilities of malfunction (as long they are not affected by mcas or other new additions). > Put people in jail for negligence The higher ups new this was a tragedy waiting to happened they just hope its going to be their successors that will have to pay. Negligence is definitely too light or a term for this. This is knowingly putting people lives in jeopardy in the name of extra % in profits.
- tzs 7y ago
  1-(1-1/10000000)^500000 = 0.048770577854436836 In other words, if all new plane models were as safe as the 737 (1 catastrophe per 10 million flights), about 5% of those new plane models would have at least one catastrophe within the first 500k flights.
  - nemonemo 7y ago
    What about two? The probability would be much lower when IID is assumed?
  - Gibbon1 7y ago
    Now ask what's the chance that a new model has serious problems? What if that is also 5%. Then you have a 50/50 chance the plane is bad news.
- lisper 7y ago
  > This is criminal behaviour, and people need to go to jail. Yes. > The MAX should never be allowed to fly again. No. Even at 20x the failure rate, flying in a Max -- even with an unmodified MCAS -- is still vastly safer than driving on a per-distance-travelled basis. Part of the problem is that commercial aviation has gotten so ridiculously safe that we've lost all perspective on risk assessment. The Max is actually fundamentally a safe plane. What made it unsafe was the totally fucked up attempt to make its flight characteristic the same as the old 737 so it and its pilots would not have to be re-certified. The right answer is to re-certify. That's expensive, but a lot cheaper than scrapping an entire fleet of brand new planes. Grounding the entire fleet forever is throwing out the baby with the bathwater.
  - rossdavidh 7y ago
    Well, given that other models exist that accomplish the same job (albeit perhaps not from Boeing), it's going to be a steep climb to get European authorities to agree to certify it, I expect. So, the correct comparison would not be to driving, but to flying in other planes with similar range that are already available. I am no expert, but I do not get the impression that it is looking good in this respect.
    - lisper 7y ago
      > it's going to be a steep climb to get European authorities to agree to certify it No doubt. > the correct comparison would not be to driving, but to flying in other planes with similar range that are already available Yes, but the correct comparison is the recertified Max, without MCAS, and with re-trained pilots. That is the alternative to scrapping the fleet.
  - 3JPLW 7y ago
    > is still vastly safer than driving on a per-distance-travelled basis I did the math one time with very conservative numbers (thinking it'd be an easy win) and got shockingly close: https://news.ycombinator.com/item?id=19983686 https://news.ycombinator.com/item?id=19983686 If you have an alternative reference or more exact numbers I'd love to see them!
tpmx 7y ago
> The November 2018 internal Federal Aviation Administration analysis, expected to be released during a House committee hearing Wednesday Is this document publicly available now? Did anyone find it?
- mzs 7y ago
  I can't find the report itself but the submitted testimony and hearing is here* In particular Collins' submission has this: >787 Lithium-Ion Battery Containment: >Before the AIR Safety Review Process was implemented in mid-2015, there were other examples of FAA management accepting applicant’s positions over the concerns of FAA technical specialists, the FAA’s aerospace safety engineers. For example, during initial certification review of the new technology 787 lithium battery system design the certification of the 787, an FAA technical specialist determined the lack of a fireproof enclosure could result in catastrophic failure due to uncontrolled fire from the battery. He proposed to FAA management that the special conditions design of for the airplane system lithium-ion battery should include a requirement for a steel containment structure that would be vented overboard. FAA management overruled the specialist. The specialist worked to modify a new special condition that was applied to the battery installation so a containment system would be required. Unfortunately, FAA managers pushed to delegate 95 percent of the certification to the applicant, including the high risk, new technology, battery installation. Without FAA safety engineer oversight, the ODA found the design without an enclosure to be compliant. Sadly, after certification, the airplane system lithium-ion battery experienced two extremely dangerous fire events and the FAA mandated the 787 fleet to be grounded. The design changes the FAA mandated to allow the 787 to fly again included a steel battery containment box that was vented overboard; as originally proposed by the FAA aerospace engineer. * https://transportation.house.gov/committee-activity/hearings/the-boeing-737-max-examining-the-federal-aviation-administrations-oversight-of-the-aircrafts-certification https://transportation.house.gov/committee-activity/hearings... edit: better link https://docs.house.gov/Committee/Calendar/ByEvent.aspx?EventID=110296 https://docs.house.gov/Committee/Calendar/ByEvent.aspx?Event...
  - redis_mlc 7y ago
    I saw the pictures of the 787 lithium-ion battery fire aftermath ... the entire equipment rack was a charred mess. In other words, a raging fire happened in the hold. The only initial San Jose Terminal 3 ($1.2+ billion) international airline was JAL, and they had to stop flying for about a year. This was a terrible blow to the airport. The engineer who advocated a battery box was not just correct, but following basic principles - even the Cessna 172 has a metal battery box: https://www.knots2u.net/battery-box-cessna-172-stainless-steel/ https://www.knots2u.net/battery-box-cessna-172-stainless-ste... Heck, I even tell IT departments to use a stainless-steel "bathtub" under water-cooled computer systems. Each time I'm called a Cassandra, until it starts leaking, then it's like, "Well of course. Anybody would do it that way." Source: commercially-licensed airplane pilot.
jdsully 7y ago
Its pretty clear reading the article that the public now has a much higher safety standard than the FAA did internally. Flying has become so safe that the public no longer considers it risky, but the FAA never updated its targets. So when Boeing wanted to trade safety for market share there was no basis to stop them. To illustrate the change in attitude it used to be common for airports to sell life insurance for the flight directly at the gate. This continued as late as the 1980s. https://www.insurancebusinessmag.com/us/news/breaking-news/a-look-back-whatever-happened-to-airport-insurance-vending-machines-22593.aspx https://www.insurancebusinessmag.com/us/news/breaking-news/a...
- ksdale 7y ago
  I feel your example just illustrates that the public has always thought flying is more dangerous than it actually is. No one would be selling life insurance if flying was as dangerous as the people buying the insurance thought it was. The FAA set a standard that makes flying way safer than driving, a risk people happily undertake all the time, but people still overestimate the risk of flying and demand more safety improvements.
  - ncallaway 7y ago
    Yea, but the parent commenter was discussing the _public's_ risk tolerance for flying. The fact that life insurance was being sold, meant the flying public _thought_ they were taking significant risks (even if they weren't). Now, such life insurance would be laughable, which means the public _does not_ think it's taking any risks. The general public's risk tolerance for flying has dropped dramatically. So, based on that, it seems the example perfectly demonstrates the point. The public thinks flying is much less of a risk now than it used to.
    - ksdale 7y ago
      Your point is well taken, thank you. Though, presumably the FAA's tolerance for risk has also dropped tremendously over the past several decades, so I feel like the more relevant comparison is the perceived risk to the actual risk. Although the public thinks the risk it's taking is much smaller, it still vastly overestimates the danger of flying. I agree completely that the public thinks flying is a lot safer than they used to, which is a change, but I think they also still really overestimate the danger, which is not a change, and which I believe is borne out by the same evidence provided by the parent, people buying life insurance when it was a bad deal and people continuing to demand that the FAA make flying so much safer than activities like driving that they engage in without a second thought. I'm also not so sure that a lot of people wouldn't still buy life insurance at the gate if it was available.
TooSmugToFail 7y ago
This was a massive shot in the foot by the FAA. Not only they neglected red flags after the first crash, remember that the idiots were also hesitating after the second one, allowing other regulators to ground the Max before them. FAA's credibility is in the dumps, along with the Boeing's.
- mzs 7y ago
  not the only case: https://transportation.house.gov/download/collins-testimony https://transportation.house.gov/download/collins-testimony edit: I found more. In particular Pierson's attachment included emails and ends with a listing of 15 emergencies over 13 months and the Summary of Subject Matter includes a quick run-down of various Boeing happening beyond the MCAS. https://docs.house.gov/Committee/Calendar/ByEvent.aspx?EventID=110296 https://docs.house.gov/Committee/Calendar/ByEvent.aspx?Event...
mzs 7y ago
We finally know fuller details* about the as proposed MCAS fix not-a-fix > There are four main changes to the B737 MAX flight control system software that have been developed to prevent future accidents like the ones that happened with the Lion Air and Ethiopian Air flights. They include the following: 1. Angle of Attack (AoA) comparison – an addition to MCAS that will now compare readings from both angle of attack sensors on the aircraft. If there is a difference of more than 5.5 degrees the speed trim system will be disabled. Also included in this change is something known as a “midvalue select” which uses data from both sensors together to create a third input that will help to filter out any AOA signal oscillatory failures or spurious sensor failures. This modification will prevent MCAS from commanding nose down trim when a single AoA sensor reports a false AoA as it happened in the two accident flights. 2. MCAS resynchronization – this change will account for manual electric trim inputs made by the pilot while MCAS is activating. It will track whatever input the pilot makes and return the pitch trim to that setting when MCAS retrims back to normal. 3. Stab trim command limit – is an addition that will limit the maximum nose down trim that the automatic flight control system can command to prevent the pitch trim from reaching an uncontrollable situation. 4. FCC monitors – software monitors have been added to the flight control computers that will cross check pitch trim commands against each other. If a difference is detected by these monitors the automatic trim functions are disabled. This protection helps prevent erroneous trim commands from a myriad of causes that could occur in the automatic flight control system. These design changes in the software that controls the automatic pitch trim features including MCAS should prevent angle of attack sensor failures from causing the pitch trim to operate when it should not. Further, they should prevent the trim from activating erroneously for other reasons as well. * https://transportation.house.gov/download/kiefer-testimony https://transportation.house.gov/download/kiefer-testimony
- linuxftw 7y ago
  Unfortunately, we don't know if flying the plane without MCAS is even safe. MCAS was required for a reason, and disabling it at an inopportune time might be disastrous.
  - DuskStar 7y ago

102 points by tompic823 7y ago

bookofjoe 7y ago

http://archive.is/JVWfg http://archive.is/JVWfg

tpmx 7y ago
Who keeps downvoting these archive.is comments and why? They are clearly very useful.
- AnimalMuppet 7y ago
  They'd be a lot more useful with some hint about what's being linked to. A bare link, with an opaque URL, and with no comment, is basically saying "trust me, this points to something relevant, but I won't tell you what". If I disagree with the poster's definition of "relevant", I've wasted my time. How about telling me what you're linking to, not just giving me a raw, opaque link?

forgingahead 7y ago

The MAX’s safety record when it was grounded, after two years in service, roughly amounted to two catastrophic accidents for every one million flights, according to estimates by industry officials relying on unofficial data. By contrast, the model of 737 that came before the MAX has suffered one fatal crash for every 10 million flights, according to data from Boeing. Put another way, the 737 Max has a statistic of 1 catastrophe per 500k flights, whilst the 737 was 1 per 10 million, basically 20 times as much. This is criminal behaviour, and people need to go to jail. The MAX should never be allowed to fly again.

jmpman 7y ago
I could see justification for clawback on any stock awarded or exercised for the executives responsible for 737 Max problems, but I don’t see any evidence that the 737 Max is unredeemable.
- addicted44 7y ago
  There likely appears to be only 1 way the Max can be redeemed, and that is for Boeing to accept it's a different enough plane that 737 pilots need new training for it.
  - deleted 7y ago
    [deleted]
  - caconym_ 7y ago
    Yes. Call it a new airplane, rip out the ridiculous and irresponsible hack that is the MCAS, and go from there.
- beamatronic 7y ago
  It’s going to make a fantastic cargo plane
  - robmiller 7y ago
    Yup, I'm sure Amazon can get them at a discount for a Prime Air fleet.
  - joachim4 7y ago
    As a consumer there is no way I will never book a flight on a 737 Max (even if those planes are allowed to fly again), and if I have the choice between flying a Boeing and an Airbus, I will buy the flight on an Airbus. Boeing clearly needs to get back the flyers trust.
    - briandear 7y ago
      Is Airbus without problems?
- adwi 7y ago
  It’s irredeemable on its name alone at this point.
LeifCarrotson 7y ago
On the other hand, generalizing from two incidents to a rate isn't great statistics. The list of accidents and incidents with the previous generation [1] shows some 9 fatal problems spread over more than a decade, which is closer to a rate. But saying that the 737 Max is known to be 20 times worse when the real value might be anywhere between 2 and 200 if it had been allowed to continue flying is a little imprecise. Put people in jail for negligence, sure. But we should be criminalizing based on that negligence and not on its results. [1]: https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Boeing_737#737_Next_Generation_(-600/-700/-800/-900)_aircraft https://en.wikipedia.org/wiki/List_of_accidents_and_incident...
- ses1984 7y ago
  If it were just 2x worse wouldn't that still be pretty horrifying? Let's not split the wrong hairs.
  - tempguy9999 7y ago
    There are degrees of wrongness.
- tpmx 7y ago
  In https://news.ycombinator.com/item?id=19437938 https://news.ycombinator.com/item?id=19437938 you wrote (8 months ago): The fault doesn't lie with the engineers who built the system...not to mention I would be very surprised if they were professionally certified. It lies with the managers who wrote the specification that said that for business reasons the new plane must not require any additional training or type certifications, and cut costs by implementing the required systems with a non-redundant sensor. (I agree.)
- me_me_me 7y ago
  Agree overall, one thing to note is that 737 Max already capitalizes on all errors corrected from 737. Max is 20 worse with all off the old system being already excluded from possibilities of malfunction (as long they are not affected by mcas or other new additions). > Put people in jail for negligence The higher ups new this was a tragedy waiting to happened they just hope its going to be their successors that will have to pay. Negligence is definitely too light or a term for this. This is knowingly putting people lives in jeopardy in the name of extra % in profits.
tzs 7y ago
1-(1-1/10000000)^500000 = 0.048770577854436836 In other words, if all new plane models were as safe as the 737 (1 catastrophe per 10 million flights), about 5% of those new plane models would have at least one catastrophe within the first 500k flights.
- nemonemo 7y ago
  What about two? The probability would be much lower when IID is assumed?
- Gibbon1 7y ago
  Now ask what's the chance that a new model has serious problems? What if that is also 5%. Then you have a 50/50 chance the plane is bad news.
lisper 7y ago
> This is criminal behaviour, and people need to go to jail. Yes. > The MAX should never be allowed to fly again. No. Even at 20x the failure rate, flying in a Max -- even with an unmodified MCAS -- is still vastly safer than driving on a per-distance-travelled basis. Part of the problem is that commercial aviation has gotten so ridiculously safe that we've lost all perspective on risk assessment. The Max is actually fundamentally a safe plane. What made it unsafe was the totally fucked up attempt to make its flight characteristic the same as the old 737 so it and its pilots would not have to be re-certified. The right answer is to re-certify. That's expensive, but a lot cheaper than scrapping an entire fleet of brand new planes. Grounding the entire fleet forever is throwing out the baby with the bathwater.
- rossdavidh 7y ago
  Well, given that other models exist that accomplish the same job (albeit perhaps not from Boeing), it's going to be a steep climb to get European authorities to agree to certify it, I expect. So, the correct comparison would not be to driving, but to flying in other planes with similar range that are already available. I am no expert, but I do not get the impression that it is looking good in this respect.
  - lisper 7y ago
    > it's going to be a steep climb to get European authorities to agree to certify it No doubt. > the correct comparison would not be to driving, but to flying in other planes with similar range that are already available Yes, but the correct comparison is the recertified Max, without MCAS, and with re-trained pilots. That is the alternative to scrapping the fleet.
- 3JPLW 7y ago
  > is still vastly safer than driving on a per-distance-travelled basis I did the math one time with very conservative numbers (thinking it'd be an easy win) and got shockingly close: https://news.ycombinator.com/item?id=19983686 https://news.ycombinator.com/item?id=19983686 If you have an alternative reference or more exact numbers I'd love to see them!

tpmx 7y ago

> The November 2018 internal Federal Aviation Administration analysis, expected to be released during a House committee hearing Wednesday Is this document publicly available now? Did anyone find it?

mzs 7y ago
I can't find the report itself but the submitted testimony and hearing is here* In particular Collins' submission has this: >787 Lithium-Ion Battery Containment: >Before the AIR Safety Review Process was implemented in mid-2015, there were other examples of FAA management accepting applicant’s positions over the concerns of FAA technical specialists, the FAA’s aerospace safety engineers. For example, during initial certification review of the new technology 787 lithium battery system design the certification of the 787, an FAA technical specialist determined the lack of a fireproof enclosure could result in catastrophic failure due to uncontrolled fire from the battery. He proposed to FAA management that the special conditions design of for the airplane system lithium-ion battery should include a requirement for a steel containment structure that would be vented overboard. FAA management overruled the specialist. The specialist worked to modify a new special condition that was applied to the battery installation so a containment system would be required. Unfortunately, FAA managers pushed to delegate 95 percent of the certification to the applicant, including the high risk, new technology, battery installation. Without FAA safety engineer oversight, the ODA found the design without an enclosure to be compliant. Sadly, after certification, the airplane system lithium-ion battery experienced two extremely dangerous fire events and the FAA mandated the 787 fleet to be grounded. The design changes the FAA mandated to allow the 787 to fly again included a steel battery containment box that was vented overboard; as originally proposed by the FAA aerospace engineer. * https://transportation.house.gov/committee-activity/hearings/the-boeing-737-max-examining-the-federal-aviation-administrations-oversight-of-the-aircrafts-certification https://transportation.house.gov/committee-activity/hearings... edit: better link https://docs.house.gov/Committee/Calendar/ByEvent.aspx?EventID=110296 https://docs.house.gov/Committee/Calendar/ByEvent.aspx?Event...
- redis_mlc 7y ago
  I saw the pictures of the 787 lithium-ion battery fire aftermath ... the entire equipment rack was a charred mess. In other words, a raging fire happened in the hold. The only initial San Jose Terminal 3 ($1.2+ billion) international airline was JAL, and they had to stop flying for about a year. This was a terrible blow to the airport. The engineer who advocated a battery box was not just correct, but following basic principles - even the Cessna 172 has a metal battery box: https://www.knots2u.net/battery-box-cessna-172-stainless-steel/ https://www.knots2u.net/battery-box-cessna-172-stainless-ste... Heck, I even tell IT departments to use a stainless-steel "bathtub" under water-cooled computer systems. Each time I'm called a Cassandra, until it starts leaking, then it's like, "Well of course. Anybody would do it that way." Source: commercially-licensed airplane pilot.

jdsully 7y ago

Its pretty clear reading the article that the public now has a much higher safety standard than the FAA did internally. Flying has become so safe that the public no longer considers it risky, but the FAA never updated its targets. So when Boeing wanted to trade safety for market share there was no basis to stop them. To illustrate the change in attitude it used to be common for airports to sell life insurance for the flight directly at the gate. This continued as late as the 1980s. https://www.insurancebusinessmag.com/us/news/breaking-news/a-look-back-whatever-happened-to-airport-insurance-vending-machines-22593.aspx https://www.insurancebusinessmag.com/us/news/breaking-news/a...

ksdale 7y ago
I feel your example just illustrates that the public has always thought flying is more dangerous than it actually is. No one would be selling life insurance if flying was as dangerous as the people buying the insurance thought it was. The FAA set a standard that makes flying way safer than driving, a risk people happily undertake all the time, but people still overestimate the risk of flying and demand more safety improvements.
- ncallaway 7y ago
  Yea, but the parent commenter was discussing the _public's_ risk tolerance for flying. The fact that life insurance was being sold, meant the flying public _thought_ they were taking significant risks (even if they weren't). Now, such life insurance would be laughable, which means the public _does not_ think it's taking any risks. The general public's risk tolerance for flying has dropped dramatically. So, based on that, it seems the example perfectly demonstrates the point. The public thinks flying is much less of a risk now than it used to.
  - ksdale 7y ago
    Your point is well taken, thank you. Though, presumably the FAA's tolerance for risk has also dropped tremendously over the past several decades, so I feel like the more relevant comparison is the perceived risk to the actual risk. Although the public thinks the risk it's taking is much smaller, it still vastly overestimates the danger of flying. I agree completely that the public thinks flying is a lot safer than they used to, which is a change, but I think they also still really overestimate the danger, which is not a change, and which I believe is borne out by the same evidence provided by the parent, people buying life insurance when it was a bad deal and people continuing to demand that the FAA make flying so much safer than activities like driving that they engage in without a second thought. I'm also not so sure that a lot of people wouldn't still buy life insurance at the gate if it was available.

TooSmugToFail 7y ago

This was a massive shot in the foot by the FAA. Not only they neglected red flags after the first crash, remember that the idiots were also hesitating after the second one, allowing other regulators to ground the Max before them. FAA's credibility is in the dumps, along with the Boeing's.

mzs 7y ago
not the only case: https://transportation.house.gov/download/collins-testimony https://transportation.house.gov/download/collins-testimony edit: I found more. In particular Pierson's attachment included emails and ends with a listing of 15 emergencies over 13 months and the Summary of Subject Matter includes a quick run-down of various Boeing happening beyond the MCAS. https://docs.house.gov/Committee/Calendar/ByEvent.aspx?EventID=110296 https://docs.house.gov/Committee/Calendar/ByEvent.aspx?Event...

mzs 7y ago

We finally know fuller details* about the as proposed MCAS fix not-a-fix > There are four main changes to the B737 MAX flight control system software that have been developed to prevent future accidents like the ones that happened with the Lion Air and Ethiopian Air flights. They include the following: 1. Angle of Attack (AoA) comparison – an addition to MCAS that will now compare readings from both angle of attack sensors on the aircraft. If there is a difference of more than 5.5 degrees the speed trim system will be disabled. Also included in this change is something known as a “midvalue select” which uses data from both sensors together to create a third input that will help to filter out any AOA signal oscillatory failures or spurious sensor failures. This modification will prevent MCAS from commanding nose down trim when a single AoA sensor reports a false AoA as it happened in the two accident flights. 2. MCAS resynchronization – this change will account for manual electric trim inputs made by the pilot while MCAS is activating. It will track whatever input the pilot makes and return the pitch trim to that setting when MCAS retrims back to normal. 3. Stab trim command limit – is an addition that will limit the maximum nose down trim that the automatic flight control system can command to prevent the pitch trim from reaching an uncontrollable situation. 4. FCC monitors – software monitors have been added to the flight control computers that will cross check pitch trim commands against each other. If a difference is detected by these monitors the automatic trim functions are disabled. This protection helps prevent erroneous trim commands from a myriad of causes that could occur in the automatic flight control system. These design changes in the software that controls the automatic pitch trim features including MCAS should prevent angle of attack sensor failures from causing the pitch trim to operate when it should not. Further, they should prevent the trim from activating erroneously for other reasons as well. * https://transportation.house.gov/download/kiefer-testimony https://transportation.house.gov/download/kiefer-testimony

linuxftw 7y ago
Unfortunately, we don't know if flying the plane without MCAS is even safe. MCAS was required for a reason, and disabling it at an inopportune time might be disastrous.
- DuskStar 7y ago