A friend of mine whom erects tower cranes here in Seattle stopped by for coffee one day last week. He brought along some pictures that I think are worth sharing. It's a tower crane that had a trolley sheave seize. They found the problem during a dismatle process and it had not been reported. It really points out the importance of inspecting your crane regularly. I once saw an operator that literally wore a harness while operating his tower crane. I never could understand how he was able to run the crane safely while being so afraid of heights. Just as importantly, he could not inspect his crane. When I say inspect, I cannot imagine not walking the jib weekly. To inspect sheaves I'll put a shoulder under the rope, push it off the sheave and give it a spin. noticable wobbles or noises cause me to look further. 10 seconds to prevent this problem. As a side note, it's irresponsible and against manufacturer recommendations to not inspect the entire crane prior to each shift. What I'm getting at is jumping on the crane from the highest point on the building is both stupid and illegal. I only wish that I had pictures of a crane that had base pins that had nearly fallen out of their holes because the operator never inspected it.
These pictures also show the importance of paying attention to your crane. There would have been telltale noises that this was happening when the bearing was failing. Then you would have been able to hear the rope sawing through the sheave. Then you would have heard and seen the rope jump from the sheave to the pin and fishplate. Then you would have seen the rope jump and slacken up when it fell 3 feet after sawing through the pin. Then you would have heard it sawing into the diamond plate on edge. This isn't difficult, it's just paying attention to something being different. When I was an operator I had a bearing going bad and it only showed under heavy loads. The technician disagreed. So I brought up my tools, called him back out and dismantled it while he was there. The metal under the bearing was oblonged and wasn't properly supporting the race. I picked out the right sheave with a small problem from the seat. That was on my first crane. I don't see an excuse for this operator and the danger here is hardware raining out of the sky. Pay attention to your rig and inspect them before you kill someone.