Cable car disaster in Italy 3

[LittleInch]

Not a huge amount of detail at the moment but a dreadful tragedy and difficult to understand how this could happen. The factor of safety on a cable car cable must be huge as it is so vital.

https://www.theguardian.com/world/2021/may/23/at-least-eight-dead-in-italian-cable-car-accident

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[1503-44]

Would not the force in the support wire be more or less equal (before braking) no matter where the gondola is, given only small changes of cable's angle between gondola and support towers?

After applying brake, the braking force must increase tension on one side of the gondola and reduce it on the other. Then the impulse travels towards the towers in both directions at the speed of sound in the cables? I'm guessing.

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[Alistair_Heaton]

Was it a jump on while its moving or it gets taken off the running wire type?

I

 

[LittleInch]

It's a two car old fashioned cable car system so each car ends up at the top and bottom at the same time and just stops next to the ramp where you get off. Then the cable direction reverses and the top car goes back down the same wire to the bottom whilst the one at the bottom goes up.

Whenever I've been on ones whilst skiing, the heavy car transporting people up the mountain slowly moves as the weight is released which can be a bit hairy.

I don't know what the angle of the main support wire is at the top and bottom. Sometimes the cars go almost horizontal over the last few metres to allow people to get on and off easily sometimes they stay at an angle.

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[LionelHutz]

It certainly would stress the tow cable if the emergency brake engaged and it held until the tow cable drive tripped on overload. It wouldn't matter how long the cable is, the same stress level would still need to be reached before the cable drive would trip on overload.

It's interesting theory, but I'm not sure if it would apply or not. Possibly, the issue was occurring as the car was being parked into the stations. If the cable is supported horizontally at the stations then there could be some mechanisms to ensure the brake doesn't lock when it's moved horizontally and even if not, there could be some kind of mechanism to lock the car into place when parked that was causing the brake to act up.

 

[waross]

Good point Lionel.
If the reduction in tension as the cars entered the terminal was causing a faulty brake to engage, then the cable would be under less tension and less liable to break as the car entered the terminal.
Hence my suggestion that for some reason the car was driven up against an end stop.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[1503-44]

I thought the brake were supposedly rendered more or less inoperable by the cable guys?
If they had some excuse like it was a bad docking manouver, they probably wouldn't be in jail.


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[LittleInch]

Do keep up.

The cars had been out of action for months due to COVID.

When they started them up again and were seemingly running test operations, the brakes on the blue car that crashed apparently started activating spuriously.

They couldn't fix it and with opening day upon them decided that they could jam open the brakes with some sort of mysterious "fork like" device because "the cable will never break".

We are speculating and I emphasis speculating here, that these apparently numerous activations of the emergency brake on only one of the cars may have been the reason why the pull cable then did break, apparently only a few metres up from the car which crashed. Maybe coincidence, maybe not. The brakes on the other car are reported to have worked, though no one said anything about how the occupants, if there were any, were later rescued, but I guess that wasn't newsworthy compared to the 14 who died.

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[LionelHutz]

The brake were supposedly rendered more or less inoperable by the thing they used to purposely lock the brake open which over-rode that safety feature. Hence why they are in jail.

What I wrote was that the tow cable might lose tension when the car is parking and that might then need a mechanism in the station to solve the brake applying problem and that mechanism could be what was acting up. Something like that being the brake issue could mean the cable braking was not the brake locking up and stressing the tow cable.

 

[Retiredat46]

It would be fairly easy to have an arrangement that would keep the emergency brake from activating when it was docked in the terminal. A pawl like this could engage a fixed pin in the dock to lock the brake out before the cable went slack. The brake would be armed as the car left the dock.

(image snipped from the post by LittleInch 25 May 21 16:48)

 

[FacEngrPE]

OK we know what happend with the safety grab - perhaps not the contributing factors why the grab was not working correctly.

Things we do not know about the pulling cable -
[ul]
[li]Did the cable part?[/li]
[li]Did the cable pull out of a anchor socket? (like the spelter socket failure at the Arecibo Observatory[/li]
[li]Did the attachment anchor in the car fail[/li]
[li]Something else?[/li]
[/ul]

Does the tow cable have the strength to handle a safety grab stop? or did the design assume a safety stop could only happen when the tow cable parts? Perhaps the designer intended for the tow cable to be replaced after a safety stop? Is the original design intent still available?

 

[dik]

...and

" The three suspects in Italy’s cable car disaster that killed 14 people were allowed to leave prison Sunday after a judge indicated that most of the blame fell on just one of them: a service technician who intentionally disabled the car’s emergency brake because it kept locking spontaneously.

Judge Donatella Banci Buonamici said there wasn’t sufficient evidence suggesting the owner of the Mottarone cable car company, Luigi Nerini, or the maintenance chief, Enrico Perocchio, knew that the technician had deactivated the brake on several occasions even before the May 23 disaster.

After evaluating prosecutors’ request for continued detention of the three, Buonamici ordered the managers freed while allowing the technician, Gabriele Tadini, to leave under house arrest. The three men, who remain under investigation, left Verbania prison early Sunday, accompanied by their lawyers."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[LionelHutz]

That just proves that shit does flow downhill.

 

[Retiredat46]

Perhaps the technician was afraid to admit he couldn't figure out why the brake wasn't working properly. That brings me to my one and only crane story, which involves people not being able to figure out the solution to a problem.

About thirty-five years ago I got the chance to climb to the machinery platform of a 50T bridge crane in a building that handled solid propellant rocket motors. The building was only a year old, and the electrical engineer I was with said they had been constantly getting calls to adjust the electronic slack-line detector that was shutting down the crane. Several other engineers and some manufacturer reps had been called in to analyze the situation, but the problems persisted.

He had attached a large-face analog meter to a circuit that monitored current to the crane motor, and I could see the needle from almost anywhere on the platform. It was moving back and forth as the crane hook was run up and down with no load. I asked about that, and he said the reps had told him it was a tight bearing somewhere in the drive train, and not related to the problem.

I started looking around while not wanting to disturb him. The only thing I could see that revolved in sync with the needle movement was the crane drum, which was about fifteen feet long and four feet in diameter. The end of the outer shell was near a railing, and I noticed the raw edge was wandering about 1/2" as the drum turned, but the machined surface and grooves were running true. I asked him to come over, and got a look that said, "Five minutes on the machinery platform, and suddenly you're a crane expert." But he showed me how to run the block up and down while he looked at the drum. He came back and said, "How the f... did we all miss that? Let's get out of here." He was really pissed, so I didn't ask any questions. Thankfully, I didn't blurt out, "I guess you never looked."

Operations in that building were soon shut down. About two months later, a new drum was delivered and installed, which required removing a section of the roof, and operations resumed. I never spoke with him or anyone else in the company about my trip to the machinery platform or the problems with the crane, so I don't know exactly how what I noticed was related to the replacement of the drum. The out-of-balance condition and the under-spec thickness of the shell under the grooves both seem like good possibilities.

 

[LittleInch]

The thing being ignored here is why they didn't know or supervise the technician or have some sort of sign off of work on safety critical systems.

It's far too easy to blame an individual rather than the system. I find it very difficult to believe that only one person knew about this.

Fac eng. Good set of questions. I don't have the answers for sure but hope the enquiry will find out. I believe the pull cable parted 20 to 30 m uphill from the cabin but haven't seen any photos.



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[MartinLe]

"wasn’t sufficient evidence suggesting [the two guys] knew that the technician had deactivated the brake" Yeah was there sufficent evidence that they knewthe brake worked? The previous problem must have been known to them, burden of proof should be on them that they had good reason to think the problem was fixed in a responsible way.

The technician claimed the other involved new about his tampering (what kind of evidence beyond his testimony would the judge accept?). He also hear d weird noises the morning of the accident, which he discarded. Still no news on why the cable broke.

Given that the cable passed a quality test last november, speculating that the brake problems manifested only since then, your speculation that the brakes stressed the tow cable appears more likely.

The "fork" appears to be, indeed, a fork: the italian word is forchettone. Two where used.

(

https://www.sueddeutsche.de/panoram...ore-mottarone-italien-ermittlungen-1.5308095)

The rescue of the passengers from the other gondola was likely no newsworthy because htey would be close to the lower station, depending on the performance of the brake *in* the station - no fancy helicopter work necessary!

As to the tow cable:
* is the load along it's length is not uniform, but different on both sides of the winch/drum at the top station
* Depending on how much mass is in the tow cable compared to a (full or empty) gondola, the load in the long stretch could be significantly higher, but also the ability to absorb shocks

 

[FacEngrPE]

It might be useful to consider wire rope inspection. I am similar with US practice, and believe EU practice under ISO 4390 is similar. Here is one manufacturers guidance.
Appropriate handling: The correct rope inspection, Verope

Here is one Magnetic wire rope tester Magnetic Rope Testing devices (MRT) Rotec

Magnetic testers can detect broken wires. They could be equipped with devices that measure wear, but there are other failure modes where visual inspection is likely still required.

Hopefully the investigation will produce some more details on this subject.

Nothing is currently published regarding the actual wire rope supplier, or the magnetic testing device used.

This information indicates that magnetic inspection is well enough developed that it is now included in the inspection standard.
ISO 4309:2017(en) Cranes — Wire ropes — Care and maintenance, inspection and discard
This document was prepared by Technical Committee ISO/TC 96, Cranes, Subcommittee SC 3, Ropes.

https://kebs.isolutions.iso.org/obp/ui#iso:std:iso:4309:ed-5:v1:en[/URL]]This fifth edition cancels and replaces the fourth edition (ISO 4309:2010), which has been technically revised and contains the following changes:

— magnetic rope test (MRT) methodology and discard criteria are introduced, as an aid to the internal inspection of wire ropes;
— guidance is given on when to use magnetic rope testing and how to combine its results with other inspection results;
— an example of an MRT report is provided.

I have attached an interesting report "Design of a Ski Lift Inspection & Maintenance System : May 9, 2018" this is a rather extensive report on US maintenance practice of ski lifts (different type from the subject lift).

A comparison of ski lift accidents to elevators both have very low but non zero accident history is telling. Cable failures are rare, but not unknown. Even at this level economics can drive inspections to be more frequent than the minimum required by law.

 

[dik]

That just proves that sh*t does flow downhill.

The gravity of the situation...


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[1503-44]

I knew somebody would have the 100MM miles statistics.

So, ski lifts travel is apparently 2x as dangerous as auto travel and 68.4% of ski lift accidents involve death. Some work needed there.

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[IRstuff]

One obvious safety improvement would be automatic safety bars; I've only had about 1% of my rides where someone actually pulled the safety bar into place. Often, I got up so early to drive to the resort that by midday, I was already bushed and half-asleep during the rides; not a formula for situational awareness and safe riding.

TTFN (ta ta for now)
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[MartinLe]

It appears the latest iteration of the ISO for cable cars doesn't require the wire brake (two redundant brakes (motor and mechanical brake) acting on the pull cable wheel are still mandatory). The rationale is that if the emergency brake fails and brakes, someone has to climb onto the car for repair - most gondolas these days don't have a conductor to do this. Also apparently "the cable never breaks"