There is a broken or deactivated emergency brake behind the accident at the Stresa-Mottarone cable car. The breaking of the hauling rope alone is not enough to explain what happened. While the “pliers” of the emergency system that should have tripped when the cable broke to brake the travel of the car on the supporting rope did not come into operation. And the question to be answered by the investigation by the prosecutor of Verbania Olimpia Bossi is one: why?
Stresa-Mottarone cable car accident: why didn’t the emergency brake calipers trigger?
The emergency brake calipers in cable cars are locked open with wedges that prevent them from closing when the lifts are closed. When reopened, the wedges are removed and it is checked that everything works. According to some rumors, reported today by La Stampa, those wedges would not have been removed by mistake. If this had happened, the consequence would be that the clamp could not have been released. But there is a sensor that should have activated the brake in any case. Why didn’t it go off?
How does the emergency brake of a cable car work? The detachment took place when the cabin was three or four meters from the arrival on the Mottarone. Having no longer a tow, the cabin slipped back and rapidly gained speed (it is assumed that it even reached 120 km / h). Then she hit hard against the last pylon of the plant and fell 30 meters. When she got to the ground she rolled for a hundred meters, stopping her run on the trees. “Every night, after the last ride, the braking system of the cable car was armed and disarmed. The technicians used wedges to keep the bites apart. Of course, if those wedges hadn’t been removed on Sunday morning, if the system hadn’t been armed , then that terrible acceleration up to the leap into the void would be explained “, says today one of the investigators a The print. There is also talk of a tool used for the empty tests of the cable car, which prevents the jaws from snapping. It is called “fork” or “iron”. That would have been forgotten, according to this hypothesis.
Franco Corso, engineer from Cavalese, Trentino, service manager of the cableways of the San Pellegrino ski area, explains today to Republic that the first mystery to be solved is the failure of the hauling rope: “These are materials with safety grade 5, that is, designed to withstand loads five times higher than the maximum expected during normal operation. The breaking of a rope is a very rare event: it can occur, theoretically, when the rope gets entangled, and the tension exceeds the safety level, or due to an external event “. While for the emergency brake there is only one explanation: “The brakes should always be activated, even during test runs, and come into operation automatically if the cabin picks up speed. But if the cabin, following a kickback, it comes off from the supporting ropes the brakes may not be effective because the jaws act on the supporting ropes “. It is possible to deactivate the emergency brake, but it can be done for maintenance and when the system is in operation it must always be activated.
The mystery of the “fork”: a human error behind the Stresa-Mottarone cable car accident?
Therefore, to date, the only possible explanation for the Stresa-Mottarone cable car accident is that of human error. Or rather: while the reason for the breaking of the hauling rope must be explained, the failure to activate the emergency system that should have stopped the cabin even with the broken cable can be explained by the failure to remove the wedges that are placed on the braking system at the end day. Piergiacomo Giuppani, electrical engineer and one of the leading experts in ropeways in Italy, says to Republic that the wedge, fork, fork or iron used to block it “would have been found. Or the investigators will find it, if it has been used”. If the iron is there, it must still be on the trolley according to the experts. The Corriere della Sera explains that the “fork” blocks the braking system, keeping the jaws of the supporting rope open.
The fork is normally used when the cabins are empty and a test drive is done without a driver to see if everything works well. In this way the operator avoids wasting time in the event that the brake is released by blocking the cabin in the middle of the path, forcing an operator to go to the site to deactivate it. This happens for example when the power fails or a hydraulic system failure occurs. If there is a fork, the car goes down anyway. If it’s not there you have to go and unlock it and it’s a complication. All this in empty cabins.
If the emergency brake had worked, the disaster would have been avoided, because the cabin would not have started to run fast and uncontrolled downstream and ended up derailing and crashing once it reached the first pylon. The presence of the fork on the emergency brake can explain the failure to activate the emergency system.
In any case, it would be a terrible and incredible coincidence of events. The pulling cable that breaks (for reasons still unknown and incomprehensible) and the emergency brake that does not activate due to human error (on that very day, just when the rope breaks). A breakdown was reported on Saturday afternoon, shortly before the closing time of the cable car. Another malfunction was reported on 7 May. All the documents of the plant, the technical data sheets and every video of the many cameras on the line were seized.
How the emergency brake of a cable car works
Yesterday the investigation also ended up all the videos from the surveillance system cameras of the structure that was impounded, also relating to the days before the fall of the gondola lift. In the low definition images you can also see the last upward stroke interrupted a few meters from the summit when the towing cable broke and the gondola lift ‘flipped’ downwards at an increasing speed since the safety braking system did not came into operation preventing the cabin from remaining anchored to the two carrying cables. In addition to the videos on Sunday, the prosecutor also decided to confiscate the videos of the previous days to understand if any anomaly that could explain the accident has occurred.
The emergency brake of a cable car is the most important safety device of any other in any vehicle that moves on wheels. They are found everywhere in this type of plant, as well as on elevators. What made them go haywire? The stories of the old maneuvers or those of the crew, who once traveled in the wagons, all go in the direction of suggesting a question. That pulls the engine that turns the whole plant.
Only with a sudden stop of the engine “maybe it is nailed” could explain the break in the cable. But it is only a hypothesis. And one of the elements that the experts will have to take into consideration, when they will finally be able to check every single part of the cabin, the control room, inspecting the cables, motors, and brakes.
And finally, there is the background to the 2015 tender that assigned the renovation works. Leitner and Ferrovie del Mottarone were candidates. Another subject was accredited but then withdrew his membership because he believed that a total restructuring of the plant was necessary, more than required by the announcement. And the costs would have been unsustainable.
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