True, but I’ve seen more than one case where the damaged item destroy (or make it unusable) even the redundant part.
Redudancy is good, but it is not a silver bullet to solve anything.
Obviously, but QA is based on statistic.
You need to destroy or damage the item tested If you want to check how a steel cable hold, You test it to the limit but after that you cannot use it anymore. So you get another one with the same specification. But if this one is defective for some reason, you would never know it until it fail.
You check security critical components to be non defective before using them. Security systems have fail-safes and redundancies.
With due diligence it is not possible for established systems to just fail in a way that is killing a dozen people. The technology isn’t new and there is plenty of cable or cog-wheel railways operating around the world, so there is established practices for security.
You check security critical components to be non defective before using them. Security systems have fail-safes and redundancies.
Obviously.
With due diligence it is not possible for established systems to just fail in a way that is killing a dozen people. The technology isn’t new and there is plenty of cable or cog-wheel railways operating around the world, so there is established practices for security.
Ok, so you have two cables, one principal and the other one as redundancy. The main one snap and in doing so damage the backup cable (or any other part that must use the backup cable) more than what falls within safety limits, so even the backup cable (or mechanism) fail. Then ? (I personally see something like that btw)
Look, I am not saying that there could not have be some problem with lack of maintenance, it looks this way, but that even fail safe and redundancy have limits to what they can do. And since some tests are destructive for the tested item you can only trust the fact that every item would be built the same way at the same quality level, which do not remove the possibility that one item end up being defective.
This is not how redundancy works on cable cars. These systems are not copies of another, but different systems with different working principles. On systems with a pulling component (like the cable here) and a suspension component (like a suspension rope or rails), a safety brake on the cabin is only held open by the tension of the pulling cable. Should the pulling force bee too low, the brake clamps onto the suspension component.
Most of the time there’s sadly no medial coverage of the safety systems. So with the accidents I followed either I don’t know why the safety systems didn’t work, or they were manipulated. For example in the 2021 case at Monte Mottarone, the brake was propped open with maintenance tools.
Given the age of the system in Lisbon, I hope it was updated to these safety standards. The most informative I could see was this image showing the underside of the wagon. It is still difficult to tell how it works in detail, but the thing protruding from the cable mount could be such a catching brake working on the inside of the cable guide I think. And to me it looks like the cable pulled out of the holder due to cracks in the holder.
Even if you have adequate maintenance , there is always the possibility you use a defective part.
That’s what redundancy is for.
True, but I’ve seen more than one case where the damaged item destroy (or make it unusable) even the redundant part.
Redudancy is good, but it is not a silver bullet to solve anything.
You can perform QA on parts.
Obviously, but QA is based on statistic.
You need to destroy or damage the item tested If you want to check how a steel cable hold, You test it to the limit but after that you cannot use it anymore. So you get another one with the same specification. But if this one is defective for some reason, you would never know it until it fail.
Not all QA is destructive. For example, X-rays can be used to detect internal cracks without damaging the sample.
Or you trust the manufacturer of the part’s QA since they should know. After all they designed and built the thing.
You check security critical components to be non defective before using them. Security systems have fail-safes and redundancies.
With due diligence it is not possible for established systems to just fail in a way that is killing a dozen people. The technology isn’t new and there is plenty of cable or cog-wheel railways operating around the world, so there is established practices for security.
Obviously.
Ok, so you have two cables, one principal and the other one as redundancy. The main one snap and in doing so damage the backup cable (or any other part that must use the backup cable) more than what falls within safety limits, so even the backup cable (or mechanism) fail. Then ? (I personally see something like that btw)
Look, I am not saying that there could not have be some problem with lack of maintenance, it looks this way, but that even fail safe and redundancy have limits to what they can do. And since some tests are destructive for the tested item you can only trust the fact that every item would be built the same way at the same quality level, which do not remove the possibility that one item end up being defective.
This is not how redundancy works on cable cars. These systems are not copies of another, but different systems with different working principles. On systems with a pulling component (like the cable here) and a suspension component (like a suspension rope or rails), a safety brake on the cabin is only held open by the tension of the pulling cable. Should the pulling force bee too low, the brake clamps onto the suspension component.
Most of the time there’s sadly no medial coverage of the safety systems. So with the accidents I followed either I don’t know why the safety systems didn’t work, or they were manipulated. For example in the 2021 case at Monte Mottarone, the brake was propped open with maintenance tools.
Given the age of the system in Lisbon, I hope it was updated to these safety standards. The most informative I could see was this image showing the underside of the wagon. It is still difficult to tell how it works in detail, but the thing protruding from the cable mount could be such a catching brake working on the inside of the cable guide I think. And to me it looks like the cable pulled out of the holder due to cracks in the holder.