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physical sensors malfunction all the time, and you have a fleet of several hundred aircraft. You would be shocked to learn how many faults an aircraft can have

by paulmd 7y ago

physical sensors malfunction all the time, and you have a fleet of several hundred aircraft. You would be shocked to learn how many faults an aircraft can have at a given time and still be allowed to take off. That's what redundancy is for, if everything had to be all-systems-go every time then you couldn't run an aircraft for a week straight. It doesn't matter as long as you have a spare, and it'll get fixed the next time you're in for maintenance. the issue with the 737 MAX is that there are only two sensors, and so far I don't see that being addressed. One sensor failing should not kill the aircraft, and it should not disable a control regime that is necessary for the aircraft to receive type certification.

avthrow9 7y ago
> You would be shocked to learn how many faults an aircraft can have at a given time and still be allowed to take off. Yep. Next time you fly, look through the cockpit door as you board for maintenance tag-outs -- usually red flags with 'INOP' labeling, most likely on the circuit breaker panels above the pilots. The Gimli Glider incident occurred partially because of a circuit breaker tag-out in the 767 fuel quantity indicator system. Aircraft manufacturers and regulators produce a Minimum Equipment List which stipulates what is required for flight. If you get your hands on one for the plane you're on, you might be surprised to discover what _isn't_ on it and what is permitted to fail. It's heavy, but here's an older American MEL for the 737 family: http://fsims.faa.gov/wdocs/mmel/b-737%20r54a.pdf http://fsims.faa.gov/wdocs/mmel/b-737%20r54a.pdf Pages 35-1 and 35-2 offer some interesting reading about the passenger oxygen system, for example.
- jdsully 7y ago
  In the Gimli glider case the aircraft wasn't legally allowed to take off. The pilots also deferred the decision on whether to take off to the maintenance crew who are not the ones authorized to make that decision. The pilots were initially demoted because of that but were restored due to public pressure. There was mitigating circumstances though, the procedures were frequently being revised (the 767 was brand new) and previously it had been permissible to take off without a fuel indicator. None of this takes away from the huge achievement of their landing. Simulator runs show the landing was near impossible. Had Captain Pearson not been an experienced glider pilot its likely they would have ditched in the river, and the historical survivability of water landings are not good.
teachrdan 7y ago
This observation is incomplete. The problem is not the absence of more sensors. It's that, in order to quickly produce (and sell) the 737-MAX, it was changed so much that its behavior was fundamentally different than that of the 737. The MCAS system, which was dependent on those two sensors, was developed to compensate for the degree to which the plane behaved differently. And Boeing underplayed how much the performance of the new plane had changed, and hid the existence of the MCAS system from commercial plane pilots, to the point where it wasn't even in their manuals. Had Boeing behaved ethically, they would have told the FAA that the new 737 required pilot training. But that would have diminished sales and hurt Boeing's stock price. That's the managerial misbehavior that many of the commenters in this thread are remarking on. https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-crashes.html https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-c...
- kayfox 7y ago
  MCAS was required for certification, in that it increases the linearity of control forces through to a stall. Without it, it becomes easier to enter a stall. MCAS was not a fix to make training lighter, the aircraft would not be able to get a type certificate without it. https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stability-part-9/ https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stabil...

by paulmd 7y ago

avthrow9 7y ago

> You would be shocked to learn how many faults an aircraft can have at a given time and still be allowed to take off. Yep. Next time you fly, look through the cockpit door as you board for maintenance tag-outs -- usually red flags with 'INOP' labeling, most likely on the circuit breaker panels above the pilots. The Gimli Glider incident occurred partially because of a circuit breaker tag-out in the 767 fuel quantity indicator system. Aircraft manufacturers and regulators produce a Minimum Equipment List which stipulates what is required for flight. If you get your hands on one for the plane you're on, you might be surprised to discover what _isn't_ on it and what is permitted to fail. It's heavy, but here's an older American MEL for the 737 family: http://fsims.faa.gov/wdocs/mmel/b-737%20r54a.pdf http://fsims.faa.gov/wdocs/mmel/b-737%20r54a.pdf Pages 35-1 and 35-2 offer some interesting reading about the passenger oxygen system, for example.

jdsully 7y ago
In the Gimli glider case the aircraft wasn't legally allowed to take off. The pilots also deferred the decision on whether to take off to the maintenance crew who are not the ones authorized to make that decision. The pilots were initially demoted because of that but were restored due to public pressure. There was mitigating circumstances though, the procedures were frequently being revised (the 767 was brand new) and previously it had been permissible to take off without a fuel indicator. None of this takes away from the huge achievement of their landing. Simulator runs show the landing was near impossible. Had Captain Pearson not been an experienced glider pilot its likely they would have ditched in the river, and the historical survivability of water landings are not good.

teachrdan 7y ago

This observation is incomplete. The problem is not the absence of more sensors. It's that, in order to quickly produce (and sell) the 737-MAX, it was changed so much that its behavior was fundamentally different than that of the 737. The MCAS system, which was dependent on those two sensors, was developed to compensate for the degree to which the plane behaved differently. And Boeing underplayed how much the performance of the new plane had changed, and hid the existence of the MCAS system from commercial plane pilots, to the point where it wasn't even in their manuals. Had Boeing behaved ethically, they would have told the FAA that the new 737 required pilot training. But that would have diminished sales and hurt Boeing's stock price. That's the managerial misbehavior that many of the commenters in this thread are remarking on. https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-crashes.html https://www.nytimes.com/2019/09/18/magazine/boeing-737-max-c...

kayfox 7y ago
MCAS was required for certification, in that it increases the linearity of control forces through to a stall. Without it, it becomes easier to enter a stall. MCAS was not a fix to make training lighter, the aircraft would not be able to get a type certificate without it. https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stability-part-9/ https://leehamnews.com/2019/02/08/bjorns-corner-pitch-stabil...