A POWER surge and a faulty circuit board in a two-year-old, $100 million radar system may have led to the stranding of thousands of passengers at Kai Tak on Saturday. Civil Aviation Department chief electronics engineer Leung Woon-yin, in charge of fixing the stricken radar which broke down for an hour at mid-day on Saturday, said the department would, if necessary, try to stabilise the incoming power supply with China Light and Power (CLP). CLP said yesterday it had checked its lines and there had been 'no problem whatsoever' with its supply to the airport. 'We believe it could be the internal system of the airport,' said a CLP spokesman. 'Up to the point of our transformer there was no problem whatsoever on Saturday. 'A surge can be caused by a lot of reasons.' Mr Leung said his staff would step up weekly checks on the equipment. The problem was partly because the radar, from US supplier Cardion, was new and settling in, he said. But the accident was unlikely to happen again. A new Mount Parker radar system was due to be in action next month and a third being built at Tai Mo Shan would begin by mid-1996, all for use by Chek Lap Kok air traffic control. 'The radar operating parameters [which had been set during installation] had changed, which caused the radar performance to be outside the tolerance and it tripped,' said Mr Leung. 'The change in parameters must be due to a power surge,' he said. The fault began at 12.20 pm on Saturday and was fixed nearly an hour later, during which time five incoming flights were diverted and 20 aircraft were held up on the tarmac. Instead of being able to use the secondary radar, which informs the ground which plane is in the air and at what distance and altitude, air traffic controllers had to rely on the primary radar which only tells distance. Nick Rhodes of Cathay Pacific said the company would ask the Civil Aviation Department about the problem, but he played down the significance.