Flights arriving at or departing from Chek Lap Kok will have to rely on a less powerful radar system for four months in 2003 during a 'system upgrade', legislators heard yesterday.
The back-up system, known as the secondary route surveillance radar, will be used while a more advanced radar is installed to replace the existing one, which is 22 years old. But it cannot detect aircraft if their transponders - the device that allows them to communicate with other aircraft and airport controllers - are out of order.
Members of the Legco economic services panel raised concerns but officials said they would assure airlines of the safety of the arrangements.
Director of Civil Aviation Albert Lam Kwong-yu told members that the present surveillance radar had been used for 22 years and maintenance was becoming more difficult as some spare parts were no longer made.
Between 1996 and 2000, there were faults with the system on average 29 times a year. But Mr Lam said that this had not caused any major problem.
The proposed replacement, costing about $105 million, will improve the stability and reliability of the system and will last for more than 20 years.
But Mr Lam said the back-up radar would have to be used from September 2003 while the new system was being installed.
The detection range of the back-up radar is as short as 140 nautical miles, compared with the existing one that can cover 200 nautical miles.
Mr Lam believed the secondary system could give sufficient support during the four months. 'We will issue notices to aircraft and airlines that we do not have [primary route surveillance] radar during that period and will tell them to be careful.'
But Choy So-yuk of the Democratic Alliance for the Betterment of Hong Kong said: 'You just told us how important that radar is, and there is an urgent need to replace it. But you now tell us that there is a time lag for the installation of the replacement system and [this system] will not be in use for four months.'
Last month, in line with new standards adopted by the International Civil Aviation Organisation, it was revealed that the vertical limit between aircraft in the skies above Hong Kong will be reduced from 600 metres to 300 metres from February 2002. This is known as Reduced Vertical Separation Minima and will allow more planes to be crammed into the sky - as well as helping airlines boost loads and save fuel by flying at optimum altitudes.
Experts have warned this will also increase the risk of wake turbulence, in which vast and powerful spirals of air from the wings can destabilise jets following behind.
The panel yesterday approved the funding but urged that the new system be installed more quickly.
Legislators were also briefed on a $51 million project to upgrade six air traffic control systems, which could allow more time for air controllers to 'execute their primary functions of air traffic planning and surveillance'.
Last month a team of British air safety experts were hired to inspect air traffic control at Chek Lap Kok. The $500,000 review was prompted in the light of 28 mid-air incidents reported since the airport opened in 1998.
Some cases involved human error, although officials insisted they were minor 'technical losses of standard' by air traffic controllers.