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Design and implementation are not completely distinct things, though. If e.g. a software company's backups were implemented solely as daily dumps to the same S

Design and implementation are not completely distinct things, though. If e.g. a software company's backups were implemented solely as daily dumps to the same SSD the database was running on, and then they implemented a more sane backup solution after the practically-inevitable data loss, would we just go "well the implementation was badly done" or would people not call it out as bad systems design? Some designs are so poorly thought through (and/or conceived for the wrong reasons to begin with, like MCAS was) that they cannot help but yield poor implementations. (Also, input from one or two sensors was far from the only problem with MCAS' implementation. The fact that it could activate multiple times and that it could trim far harder and faster than human pilots could manually trim were equally contributors to making the saga a tragedy).

WalterBright 1y ago
> conceived for the wrong reasons The reasons were correct. Making the MAX behave, as far as the pilots were concerned, like other models of the 737 makes the airplane safer. Many crashes have resulted from pilots getting confused about which airplane they are flying. The design particulars, however, were incorrect. That is Boeing's fault. > trim far harder and faster The 737 has only one electric trim rate - on and off. It does not trim harder or faster than the autopilot trim or the thumb switch trim. The signal all boils down to a wire that has signals "trim on / trim off". The thumb switches sit on the path of that wire, so when they activate they override the autopilot and MCAS. The cutoff switch is downstream of that. Part of the reason the manual trim wheel could not be moved is the airplane was overspeeding due to being (incorrectly) at full throttle. Overspeeding greatly increases the force on the stabilizer, making it much harder to move. In the EA flight, the overspeed warning horn could be heard on the voice recorder.
- filleduchaos 1y ago
  The only reason why "making it behave like other 737s" was even a goal to begin with was so that it wouldn't need to undergo more rigorous certification and pilots wouldn't have to undergo comprehensive training to get rated for the 737 MAX. This was very explicitly because pilots _didn't_ need to do that to get rated for the competing A320neo family, not because Airbus did absurd shenanigans to make it handle the same as the A320ceos, but because they weren't desperately holding on to a 1960s design that was amongst other things so low to the ground that the new engines being fitted to it couldn't actually fit. That has nothing to do with actual safety and everything to do with profit. > The 737 has only one electric trim rate - on and off. It does not trim harder or faster than the autopilot trim or the thumb switch trim Is there a reason you cut off the sentence you're quoting before the part that says "than human pilots could MANUALLY trim" and started talking about the electric trim rate instead? Because that part of the sentence was written for a reason - the overwhelmingly more relevant reason why the manual trim wheel would not have saved them is that they would have had to crank it 15 times to trim just one degree (and they were much more than one degree out of trim, due to MCAS activating for five full seconds each time). Even if they weren't already overspeeding, it is highly doubtful that they would have won the battle to keep the aircraft in the air given their proximity to the ground + struggle to keep the nose above the horizon with two pilots versus one. Also mind you by the time they entered the overspeed condition, they had already had the stick shaker going (due to the faulty AoA sensor, with no IAS disagree alert) and had had 2 MCAS activations to deal with, with the autothrottle failing to reduce the thrust to the climb detent because the very same faulty AoA sensor.

WalterBright 1y ago

> conceived for the wrong reasons The reasons were correct. Making the MAX behave, as far as the pilots were concerned, like other models of the 737 makes the airplane safer. Many crashes have resulted from pilots getting confused about which airplane they are flying. The design particulars, however, were incorrect. That is Boeing's fault. > trim far harder and faster The 737 has only one electric trim rate - on and off. It does not trim harder or faster than the autopilot trim or the thumb switch trim. The signal all boils down to a wire that has signals "trim on / trim off". The thumb switches sit on the path of that wire, so when they activate they override the autopilot and MCAS. The cutoff switch is downstream of that. Part of the reason the manual trim wheel could not be moved is the airplane was overspeeding due to being (incorrectly) at full throttle. Overspeeding greatly increases the force on the stabilizer, making it much harder to move. In the EA flight, the overspeed warning horn could be heard on the voice recorder.

filleduchaos 1y ago
The only reason why "making it behave like other 737s" was even a goal to begin with was so that it wouldn't need to undergo more rigorous certification and pilots wouldn't have to undergo comprehensive training to get rated for the 737 MAX. This was very explicitly because pilots _didn't_ need to do that to get rated for the competing A320neo family, not because Airbus did absurd shenanigans to make it handle the same as the A320ceos, but because they weren't desperately holding on to a 1960s design that was amongst other things so low to the ground that the new engines being fitted to it couldn't actually fit. That has nothing to do with actual safety and everything to do with profit. > The 737 has only one electric trim rate - on and off. It does not trim harder or faster than the autopilot trim or the thumb switch trim Is there a reason you cut off the sentence you're quoting before the part that says "than human pilots could MANUALLY trim" and started talking about the electric trim rate instead? Because that part of the sentence was written for a reason - the overwhelmingly more relevant reason why the manual trim wheel would not have saved them is that they would have had to crank it 15 times to trim just one degree (and they were much more than one degree out of trim, due to MCAS activating for five full seconds each time). Even if they weren't already overspeeding, it is highly doubtful that they would have won the battle to keep the aircraft in the air given their proximity to the ground + struggle to keep the nose above the horizon with two pilots versus one. Also mind you by the time they entered the overspeed condition, they had already had the stick shaker going (due to the faulty AoA sensor, with no IAS disagree alert) and had had 2 MCAS activations to deal with, with the autothrottle failing to reduce the thrust to the climb detent because the very same faulty AoA sensor.