5 ms·

Technically - easier. They have to remove MCAS and retrain the pilots as a new type. But rebuilding the trust will be harder.

cesarb 7y ago
It might not be that easy. Making the 737 MAX a new type could mean losing grandfathered exemptions from new rules, which might require several other changes to the aircraft.
- anticensor 7y ago
  It is not; in fact, it does violate whole books of rules which has been grandfathered to by exemptions.
  - chx 7y ago
    OMG do you have links where I can read more? So that's why they did this whole mess! It never made sense to me that saving a little money on certification was the reason for this but if the plane couldn't be certified today as a new plane ... that'd make a lot more sense.
    - mopsi 7y ago
      https://www.seattletimes.com/business/boeing-aerospace/boeing-pushed-faa-to-arelax-737-max-certification-requirements-for-crew-alerts/ https://www.seattletimes.com/business/boeing-aerospace/boein...
    - thombat 7y ago
      As an example of the sort of old design which used to be grandfathered in there's the Helios crash [1], where on a plane built in 1997 the exact same alarm horn was used for two situations (configuration error during take-off, and loss of cabin pressure at altitude). The old-school reasoning was that this wouldn't be a problem since the two situations are necessarily disjoint. However as the accident investigation board wrote: "Most pilots are not very likely to experience a cabin pressurization problem and the associated warning horn at any time during their line flying. The Board also considered the role of stress that probably further contributed to the possible confusion of the two meanings of the warning horn. In general, stress, such as that caused by the onset of a loud, distracting alarm in the cockpit, combined with the element of surprise, is known to lead to automatic reactions. Automatic reactions, in turn, are typically those that result from experience and frequency of encounter and are therefore not always appropriate. The Board considered that the flight crew may have automatically reverted to a reaction based on memory before consciously processing the source and significance of the stress factor. This would also explain why the flight crew failed to realize the improbability of their interpretation of the horn as a takeoff configuration horn and why they failed to move on to gathering information for a new, correct diagnosis of the problem at hand." That particular stable door got closed, but at the time it was cited by pilots as an example of legacy design that wouldn't have been permitted on a clean-sheet airliner. [1] https://en.wikipedia.org/wiki/Helios_Airways_Flight_522#Flight_and_crash https://en.wikipedia.org/wiki/Helios_Airways_Flight_522#Flig...
deleted 7y ago
[deleted]
masklinn 7y ago
The source, the entire cause of this mess, was to have the 737 MAX not be a new type. If the "fix" is to not do that, then the 737 MAX is not fixable because it loses the entire reason for its existence.
- dodobirdlord 7y ago
  > The source, the entire cause of this mess, was to have the 737 MAX not be a new type. If the "fix" is to not do that, then the 737 MAX is not fixable because it loses the entire reason for its existence. There are a ton of existing 737 MAX, and Boeing's production lines are all geared up to produce more. The MCAS etc are there so that it could be called a 737, but the "entire reason for its existence" was to mount larger more fuel-efficient engines.
  - masklinn 7y ago
    > the "entire reason for its existence" was to mount larger more fuel-efficient engines. On a 737 type. Not on a completely different type which would require retraining all 737 crew and lose months worth of flight time. Even less so for companies like Southwest which fly 737s exclusively.
    - mrep 7y ago
      Still would be a lot cheaper than scrapping 80 billion dollars worth of planes already built.
      - masklinn 7y ago
        Seems like a prime demo of sunk costs fallacy.
        mrep 7y ago
        Half of that is from unsold planes that they built after it got grounded. So for those, their options are retrain pilots and make 40 billion in sales vs not retraining pilots and scrapping the planes/reusing what you can. Pretty sure the 40 billion in sales will easily be greater than retraining the pilots and whatever scrap they could use. Also, "Typically, once an airline takes the aircraft, Boeing makes some guarantees in terms of the performance of that aircraft, and one of them is that the aircraft should be airworthy," says Chris Higgins, an analyst at Morningstar [0]. So even the other half that is already sold isn't necessarily sunk for them as they have contractual obligations that will cost them if the planes have to get scrapped. [0]: https://www.npr.org/2019/03/13/703189895/for-boeing-costs-of-grounding-jets-have-only-just-begun https://www.npr.org/2019/03/13/703189895/for-boeing-costs-of...
carlmr 7y ago
Without MCAS and with retaining you'd need to redesign the whole mechanics properly.
kozak 7y ago
Or add a third angle of attack sensor.
- JshWright 7y ago
  Even adding a second (as a standard, not an upgrade) would be a start...
  - anticensor 7y ago
    There are already two of them installed in each plane.
    - Zak 7y ago
      Two are installed, but MCAS only used one, and the disagree warning light was not operational despite the documentation saying that it was.
phire 7y ago
You can't certify the plane without MCAS or some replacement. MCAS wasn't added because the plane didn't fly the same as the 737. MCAS was added because the plane didn't fly the same as all other certifiable aircraft. It doesn't meet FAA regulations on how the controls need to feel when approaching stall. The type rating mess only caused Boeing to hide MCAS from pilots. This triggered various dangerous design decisions, including designing it to be impossible to disable and making it only take data from one sensor.
Zak 7y ago
The aircraft could probably be safe and pass certification with MCAS in place, but the following issues made it dangerous: * It was undocumented. * It had too much control authority. It was able to adjust the trim such that the elevator could not overcome the trim's pitch-down force, and such that the average pilot did not have enough strength to use the manual trim wheel to neutralize the trim in a dive. * They removed the switch to turn it off. On older 737s, there's one switch to turn off automated control of stabilizer trim, and another to disconnect power to the motor, completely disabling electric trim. On the Max, both switches perform the latter function. * They made it rely on only one sensor. I can't imagine the logic for that since two sensors are physically present, and damage to AOA sensors is not rare. * The AOA disagree warning light, which would have clued pilots in to the presence of a faulty sensor was not present in most aircraft, despite documentation to the contrary.
- cesarb 7y ago
  > They made it rely on only one sensor. I can't imagine the logic for that since two sensors are physically present, and damage to AOA sensors is not rare. The logic for that is really simple: each sensor is wired to one of the two computers. Each computer uses its own sensor. This was an already existing design, MCAS is just a new function added to these computers. (AFAIK, other aircraft like Airbus have multiple sensors wired to each computer, so for them it would be natural to use more than one sensor.)
  - Zak 7y ago
    That makes a lot of sense actually; it wasn't a deliberate decision, just the path of least resistance.
  - phire 7y ago
    Both computers have access to both sensor's data. The computers are networked together. This is how they implement the AoA disagree function (the one which was broken in 90% of MAXes for unrelated reasons). It's also how they managed to implement a software update which makes MCAS take data from both sensors. The logic for not implementing both sensors is much more insidious. If you implement both sensors, then you have to deal with the case that infomation from sensors might disagree. The computer has no idea sensor is providing correct data, so the only thing it can really do is disable itself when the sensors disagree. If MCAS has the ability to disable itself, then it must provide feedback to pilots it has done so, and have pilots follow some procedures. If there were procedures, then Boeing would have to add pilot training about what MCAS was and how things would be different when it disabled itself. Boeing made it rely on only a single sensor to bypass training requirements.

cesarb 7y ago

It might not be that easy. Making the 737 MAX a new type could mean losing grandfathered exemptions from new rules, which might require several other changes to the aircraft.

anticensor 7y ago
It is not; in fact, it does violate whole books of rules which has been grandfathered to by exemptions.
- chx 7y ago
  OMG do you have links where I can read more? So that's why they did this whole mess! It never made sense to me that saving a little money on certification was the reason for this but if the plane couldn't be certified today as a new plane ... that'd make a lot more sense.
  - mopsi 7y ago
    https://www.seattletimes.com/business/boeing-aerospace/boeing-pushed-faa-to-arelax-737-max-certification-requirements-for-crew-alerts/ https://www.seattletimes.com/business/boeing-aerospace/boein...
  - thombat 7y ago
    As an example of the sort of old design which used to be grandfathered in there's the Helios crash [1], where on a plane built in 1997 the exact same alarm horn was used for two situations (configuration error during take-off, and loss of cabin pressure at altitude). The old-school reasoning was that this wouldn't be a problem since the two situations are necessarily disjoint. However as the accident investigation board wrote: "Most pilots are not very likely to experience a cabin pressurization problem and the associated warning horn at any time during their line flying. The Board also considered the role of stress that probably further contributed to the possible confusion of the two meanings of the warning horn. In general, stress, such as that caused by the onset of a loud, distracting alarm in the cockpit, combined with the element of surprise, is known to lead to automatic reactions. Automatic reactions, in turn, are typically those that result from experience and frequency of encounter and are therefore not always appropriate. The Board considered that the flight crew may have automatically reverted to a reaction based on memory before consciously processing the source and significance of the stress factor. This would also explain why the flight crew failed to realize the improbability of their interpretation of the horn as a takeoff configuration horn and why they failed to move on to gathering information for a new, correct diagnosis of the problem at hand." That particular stable door got closed, but at the time it was cited by pilots as an example of legacy design that wouldn't have been permitted on a clean-sheet airliner. [1] https://en.wikipedia.org/wiki/Helios_Airways_Flight_522#Flight_and_crash https://en.wikipedia.org/wiki/Helios_Airways_Flight_522#Flig...

deleted 7y ago

[deleted]

masklinn 7y ago

The source, the entire cause of this mess, was to have the 737 MAX not be a new type. If the "fix" is to not do that, then the 737 MAX is not fixable because it loses the entire reason for its existence.

dodobirdlord 7y ago
> The source, the entire cause of this mess, was to have the 737 MAX not be a new type. If the "fix" is to not do that, then the 737 MAX is not fixable because it loses the entire reason for its existence. There are a ton of existing 737 MAX, and Boeing's production lines are all geared up to produce more. The MCAS etc are there so that it could be called a 737, but the "entire reason for its existence" was to mount larger more fuel-efficient engines.
- masklinn 7y ago
  > the "entire reason for its existence" was to mount larger more fuel-efficient engines. On a 737 type. Not on a completely different type which would require retraining all 737 crew and lose months worth of flight time. Even less so for companies like Southwest which fly 737s exclusively.
  - mrep 7y ago
    Still would be a lot cheaper than scrapping 80 billion dollars worth of planes already built.
    - masklinn 7y ago
      Seems like a prime demo of sunk costs fallacy.
      - mrep 7y ago
        Half of that is from unsold planes that they built after it got grounded. So for those, their options are retrain pilots and make 40 billion in sales vs not retraining pilots and scrapping the planes/reusing what you can. Pretty sure the 40 billion in sales will easily be greater than retraining the pilots and whatever scrap they could use. Also, "Typically, once an airline takes the aircraft, Boeing makes some guarantees in terms of the performance of that aircraft, and one of them is that the aircraft should be airworthy," says Chris Higgins, an analyst at Morningstar [0]. So even the other half that is already sold isn't necessarily sunk for them as they have contractual obligations that will cost them if the planes have to get scrapped. [0]: https://www.npr.org/2019/03/13/703189895/for-boeing-costs-of-grounding-jets-have-only-just-begun https://www.npr.org/2019/03/13/703189895/for-boeing-costs-of...

carlmr 7y ago

Without MCAS and with retaining you'd need to redesign the whole mechanics properly.

kozak 7y ago

Or add a third angle of attack sensor.

JshWright 7y ago
Even adding a second (as a standard, not an upgrade) would be a start...
- anticensor 7y ago
  There are already two of them installed in each plane.
  - Zak 7y ago
    Two are installed, but MCAS only used one, and the disagree warning light was not operational despite the documentation saying that it was.

phire 7y ago

You can't certify the plane without MCAS or some replacement. MCAS wasn't added because the plane didn't fly the same as the 737. MCAS was added because the plane didn't fly the same as all other certifiable aircraft. It doesn't meet FAA regulations on how the controls need to feel when approaching stall. The type rating mess only caused Boeing to hide MCAS from pilots. This triggered various dangerous design decisions, including designing it to be impossible to disable and making it only take data from one sensor.

Zak 7y ago

The aircraft could probably be safe and pass certification with MCAS in place, but the following issues made it dangerous: * It was undocumented. * It had too much control authority. It was able to adjust the trim such that the elevator could not overcome the trim's pitch-down force, and such that the average pilot did not have enough strength to use the manual trim wheel to neutralize the trim in a dive. * They removed the switch to turn it off. On older 737s, there's one switch to turn off automated control of stabilizer trim, and another to disconnect power to the motor, completely disabling electric trim. On the Max, both switches perform the latter function. * They made it rely on only one sensor. I can't imagine the logic for that since two sensors are physically present, and damage to AOA sensors is not rare. * The AOA disagree warning light, which would have clued pilots in to the presence of a faulty sensor was not present in most aircraft, despite documentation to the contrary.

cesarb 7y ago
> They made it rely on only one sensor. I can't imagine the logic for that since two sensors are physically present, and damage to AOA sensors is not rare. The logic for that is really simple: each sensor is wired to one of the two computers. Each computer uses its own sensor. This was an already existing design, MCAS is just a new function added to these computers. (AFAIK, other aircraft like Airbus have multiple sensors wired to each computer, so for them it would be natural to use more than one sensor.)
- Zak 7y ago
  That makes a lot of sense actually; it wasn't a deliberate decision, just the path of least resistance.
- phire 7y ago
  Both computers have access to both sensor's data. The computers are networked together. This is how they implement the AoA disagree function (the one which was broken in 90% of MAXes for unrelated reasons). It's also how they managed to implement a software update which makes MCAS take data from both sensors. The logic for not implementing both sensors is much more insidious. If you implement both sensors, then you have to deal with the case that infomation from sensors might disagree. The computer has no idea sensor is providing correct data, so the only thing it can really do is disable itself when the sensors disagree. If MCAS has the ability to disable itself, then it must provide feedback to pilots it has done so, and have pilots follow some procedures. If there were procedures, then Boeing would have to add pilot training about what MCAS was and how things would be different when it disabled itself. Boeing made it rely on only a single sensor to bypass training requirements.