Police are likely to call on the PLA for help if a no-fly zone is declared over Wan Chai as an anti-terrorist measure during the World Trade Organisation meeting in December, according to a military expert. The role of the People's Liberation Army would probably be confined to electronic surveillance of airspace rather than air patrols, said PLA expert Ma Ding-shing. Police suggested last month a no-fly zone be considered to protect delegates to the six-day WTO meeting at the Convention and Exhibition Centre. Police Tactical Unit Commandant Bill Suen told lawmakers that a no-fly zone would be established if intelligence indicated a possible terror threat from the air. It has become commonplace to secure the airspace directly above high-profile international meetings. 'It has become a standard operating procedure,' said Bradley Allan, director of consulting for security firm Pinkerton. 'Post 9/11, there is the risk of a terrorist attack. There is also the risk that at these conferences, the protesters will hire an aircraft to drop leaflets.' During the World Economic Forum in Davos in January, the Swiss authorities strictly regulated helicopter traffic ferrying dignitaries, and civil aircraft were allowed in and out of the 'exclusion zone' subject to identification. Legislative Council security panel chairman James To Kun-sun said it was likely at least limited airspace restrictions had been put in place during previous high-profile events in Hong Kong. This may have involved the diversion or suspension of helicopter ferries operating from the harbour, he said. Security officials have refused to elaborate on plans for an exclusion zone. But Mr Ma said if a no-fly zone were implemented, the local PLA garrison would likely be asked to assist. 'If things do heat up, it's also likely that we will see air defences in the airspace directly above and near Wan Chai beefed up,' he said, adding this would mainly involve monitoring equipment. Operationally, it would likely involve the diversion of civilian air traffic. The critical question was whether the exclusion zone would be limited to a few square kilometres above Wan Chai or encompass the city's entire airspace, Mr Ma said.