Cable cars are used safely around the world every day. But by their nature, being high off the ground and usually above dangerous terrain, the results of any accident can be particularly severe.

In March this year, a US marine pilot was acquitted of all charges relating to the deaths of 20 people when his jet sliced through cables in the Italian town of Cavalese. Rescuers in the ski resort found no survivors in the wreckage.

Relatives of those who died were outraged by the not guilty verdict on Marine Captain Richard Ashby by a US military jury on charges of involuntary manslaughter, destruction of property and dereliction of duty.

Earlier this week 40 tourists were rescued from a cable car in Norway, in which they had been stranded for almost eight hours.

The scene of the crash at Cermis

The car was stuck 150ft in the air on mountain slopes near Tromso. Some of the tourists were winched out of the car by helicopter, others were brought out by mountain rescue climbers using harnesses.

An inquiry into why the cables seized up is underway, and is expected to focus on whether the summer heat had an effect.

An EU directive into the management and safety standards of cableways - a term which includes chairlifts and gondolas as well as cable cars - is in the pipeline.

In the UK there are no official regulations governing their safety.

Instead the burden rests on operators, who have a duty of care to ensure public safety, says Terry Williams, an inspector with the Health and Safety Executive.

It means having insurance, performing regular safety inspections, and checking the state of the wire rope which supports the cars.

Cables remain popular - artist's impression of one to be built at London's Millennium Dome

"These ropes have tremendous breaking strain which you can actually inspect and see how close it is to breaking," he says.

The Nevis Range Development Company operates one of only three gondola, or enclosed chairlift, systems in the UK.

Spokeswoman Mariam Austin says the company has three full-time engineers who perform manufacturer-approved checks and log them daily.

Electronic sensors at both ends of the 2.5km gondola, which transports skiers 2,150 metres, check for changes in wind speed.

Because ropeways are highly exposed to the elements, strong gusts pose a major hazard.