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That's not entirely true. Any reasonably complex system will almost certainly have single points of failure, including airliners. Those single points of failure

That's not entirely true. Any reasonably complex system will almost certainly have single points of failure, including airliners. Those single points of failures might be very unlikely, but they are still there. E.g. what if the front fell off?

WalterBright 5y ago
It is entirely true. Source: I worked on 757 flight controls design for 3 years. > what if the front fell off? All structural components are redundant and have redundant attachments. The wing spars are doubled, for example.
- deleted 5y ago
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- histriosum 5y ago
  There are certainly single points of failure in airliner design. An example that springs to mind is the stabilizer trim jackscrew. There are supporting systems which try to mitigate the risk of failure or the likelihood of failure, but bottom line, if the jackscrew fails, there is no redundancy. You've lost stab trim, potentially making the situation unrecoverable. Of course Alaska 261 is one such example of a jackscrew failure.
  - WalterBright 5y ago
    I worked for 3 years on the design the 757 stab trim jackscrew. We considered every failure, and had redundancy for it. The AL flight cracked its nut, and the balls fell out. I don't know the details of that design, but on the 757 the ice scrapers on both sides of the nut will hold the nut in place if the balls fall out. If I recall correctly, if the AL pilot had simply left the trim system alone after it failed, and landed the airplane, it would have been fine. Instead, he kept fiddling with it, driving it up and down, until it tore the nut to pieces. The loud screech it made when running in a half broken configuration should have chilled anyone's blood to bone at 30,000 feet. As that incident, and the later MAX crashes clearly demonstrated, once something goes wrong with the stab trim system, you move it only enough to get the airplane into a flyable state. Then, you turn it off and leave it the frack alone. Land it, and let the mechanics figure it out with it safely in the hangar. One incident where the stab trim failed and the poor pilots were just passengers to their doom was that 747 that took off from the base, and some tank in the cargo hold broke loose, slid back, smashed through the bulkhead and broke off the whole stab trim system. That really wasn't the stab trim system's fault, you can't really design for a tank falling on it. It was the fault of no redundancy in the straps holding the tank in place. The video of the crash, shown endlessly on the news, makes my gut turn to water.
    - histriosum 5y ago
      I fully agree that the risk tradeoffs made on these designs are highly unlikely to fail. The point is, though, that if they DO fail there IS NO redundancy. There aren't two jackscrew mechanisms. It's a single point of failure. Highly reliable single points of failure don't become redundant because of their high reliability -- they are still single points of failure. And sometimes those must be accepted -- even in safety critical systems.

WalterBright 5y ago

It is entirely true. Source: I worked on 757 flight controls design for 3 years. > what if the front fell off? All structural components are redundant and have redundant attachments. The wing spars are doubled, for example.

deleted 5y ago
[deleted]
histriosum 5y ago
There are certainly single points of failure in airliner design. An example that springs to mind is the stabilizer trim jackscrew. There are supporting systems which try to mitigate the risk of failure or the likelihood of failure, but bottom line, if the jackscrew fails, there is no redundancy. You've lost stab trim, potentially making the situation unrecoverable. Of course Alaska 261 is one such example of a jackscrew failure.
- WalterBright 5y ago
  I worked for 3 years on the design the 757 stab trim jackscrew. We considered every failure, and had redundancy for it. The AL flight cracked its nut, and the balls fell out. I don't know the details of that design, but on the 757 the ice scrapers on both sides of the nut will hold the nut in place if the balls fall out. If I recall correctly, if the AL pilot had simply left the trim system alone after it failed, and landed the airplane, it would have been fine. Instead, he kept fiddling with it, driving it up and down, until it tore the nut to pieces. The loud screech it made when running in a half broken configuration should have chilled anyone's blood to bone at 30,000 feet. As that incident, and the later MAX crashes clearly demonstrated, once something goes wrong with the stab trim system, you move it only enough to get the airplane into a flyable state. Then, you turn it off and leave it the frack alone. Land it, and let the mechanics figure it out with it safely in the hangar. One incident where the stab trim failed and the poor pilots were just passengers to their doom was that 747 that took off from the base, and some tank in the cargo hold broke loose, slid back, smashed through the bulkhead and broke off the whole stab trim system. That really wasn't the stab trim system's fault, you can't really design for a tank falling on it. It was the fault of no redundancy in the straps holding the tank in place. The video of the crash, shown endlessly on the news, makes my gut turn to water.
  - histriosum 5y ago
    I fully agree that the risk tradeoffs made on these designs are highly unlikely to fail. The point is, though, that if they DO fail there IS NO redundancy. There aren't two jackscrew mechanisms. It's a single point of failure. Highly reliable single points of failure don't become redundant because of their high reliability -- they are still single points of failure. And sometimes those must be accepted -- even in safety critical systems.