It's as much a part of the flying experience as take-off and landing, but the in-flight movie - popular with the public and a selling point for airlines - is now, say some experts, a safety hazard.

According to figures published this week, airline companies in the States have reported 60 incidents of malfunctioning entertainment systems in the past five years, causing sparks, smoke and even fires. One incident involved a Boeing 757 whose pilots were forced to divert the plane.

Thirteen such incidents have been reported to the US Federal Aviation Administration in the last six months.

The Canadian Transportation Safety Board has reported that a Swissair jet which crashed in 1998, killing 229 people, was caused by problems with the wiring of the in-flight entertainment system. Manufacturers claim that the Swissair tragedy was an aberration and that modern in-flight entertainment systems pose no threat - an assertion supported yesterday by the FAA, which, incidentally, has issued 22 orders to ban, modify or repair certain systems.

Aviation authorities in Australia last week ordered airline companies to modify the electrical wiring on systems fitted to Boeing 767 aircraft.

'The time has long past when we can consider these systems risk-free,' said Jim Shaw, a pilot and safety expert for the US Airline Pilots Association. 'I know of many instances where problems with in-flight entertainment systems created smoke and fire events.'

Alex Richman, an aviation safety software developer, said the problem was far more extensive: 'The 60 reports that are on record are probably the tip of the iceberg. More incidents probably go unreported than are reported.'

More than one-third of the world's planes carry in-flight movie systems - many of them fitted into older aircraft. Fitting new units to an aircraft adds an extra four miles of wiring. One solution would be to use fibre-optic cables instead of electrical wires.