I know that I am only reading the news and not involved but ... folks are suggesting here that the helo was ferrying liquid concrete in a kettle. The same BBC web report from which I posted that the cross-route had been approved, says this in the first paragraph:
helicopter accidentally dropped a concrete block on a cable car
Another paragraph says,
The block, which was to be used for construction, hit one gondola, sending it plunging down. Two other gondolas swung violently, hurling people out.
Of course, they may have misunderstood that that it was actually a kettle. Perhaps some other reports from closer to the site will be able to confirm. To the people involved, it's immaterial but - in trying to understand the picture of activity - might it be different if they were moving pre-cast blocks, as opposed to liquid concrete?