I beg to differ with some of the opinions that have been posted here by various individuals.
There would be NO circumstances that should allow an external load to be flown over an operational cable car. It is precisely because this kind of activity is not permitted, that you never read about accidents of this kind. Dealing with a construction crew and personnel involved with the operation on the ground, is an entirely different matter than flying an external load over the general public.
The onus is on the Operator to ensure the safety not only of their own crew members, but also the public who are an innocent party to the operation that is going on around them. The initial safety consideration must always be the worst case scenario. If a risk analysis originates from this worst case, even the most unlikely "freak accident" is eliminated at stage one of the operational planning phase.
I have set up and executed hundreds of external load jobs, and cannot tell you of a single one where anything like this has occurred, would be considered, or would be permitted. It is an unacceptable practice to fly an external load over an area where members of the public are located.
The issue is not the cause of the load release. It is in the operational and safety aspects in the set-up of the job. It is a truly tragic occurence.
Just for reference, it might be worth considering the FAA rules pertaining to external loads - pretty practical requirements, pretty practical advice.
Extract from FAR Part 133
(d) Notwithstanding the provisions of part 91 of this chapter, the holder of a Rotorcraft External-Load Operator Certificate may conduct (in rotorcraft type certificated under and meeting the requirements of part 27 or 29 of this chapter, including the external-load attaching means) rotorcraft external-load operations over congested areas if those operations are conducted without hazard to persons or property on the surface and comply with the following:
(1) The operator must develop a plan for each complete operation, coordinate this plan with the FAA Flight Standards District Office having jurisdiction over the area in which the operation will be conducted, and obtain approval for the operation from that district office. The plan must include an agreement with the appropriate political subdivision that local officials will exclude unauthorized persons from the area in which the operation will be conducted, coordination with air traffic control, if necessary, and a detailed chart depicting the flight routes and altitudes.
(2) Each flight must be conducted at an altitude, and on a route, that will allow a jettisonable external load to be released, and the rotorcraft landed, in an emergency without hazard to persons or property on the surface.
(e) Notwithstanding the provisions of part 91 of this chapter, and except as provided in Sec. 133.45(d), the holder of a Rotorcraft External-Load Operator Certificate may conduct external-load operations, including approaches, departures, and load positioning maneuvers necessary for the operation, below 500 feet above the surface and closer than 500 feet to persons, vessels, vehicles, and structures, if the operations are conducted without creating a hazard to persons or property on the surface.