The Executive Council is expected to approve tomorrow a HK$136 billion proposal to build a third runway at Chek Lap Kok.
If it is approved, the government will then seek the first batch of funding from lawmakers to kick-start the project's early design works, conduct a study on the project's financing options and carry out an environmental impact assessment.
The Airport Authority estimates the environmental assessment to cost about HK$100 million and take 18 months to two years to complete.
While the project appears to be moving ahead, there are still many questions about the proposed third runway's ability to meet higher air quality benchmarks, and how the costs of doing so would add to what is already forecast to be the city's most expensive project to date.
There is also the issue about whether the runway could be operational before the existing two runways reach full capacity - projected in eight years.
Wilson Fung Wing-yip, the authority's executive director, has warned that the project's cost - which has already been adjusted for inflation over the next decade - would rise further when engineers set out remedial environmental measures. In a study commissioned by WWF Hong Kong, University of British Columbia researchers said officials had underestimated the impact of reclamation on Hong Kong's fisheries.
They said reclamation of 650 hectares to the northeast of the airport was likely to reduce catches by 0.44 per cent a year, amounting to HK$48 million in catches over 18 years, or five times more than the official projection.
William Yu Yuen-ping, head of WWF's climate programme, said he also feared the authority would 'play games with the numbers' to meet the more stringent air quality guidelines issued by the government in January.
'Despite an increase in flight movements, they [the authority] often cite the evolution in flight standards and adoption of biofuels as reasons why air quality will remain largely the same 20 years from now,' Yu said.
'But no one can actually project clearly how fast biofuels will be adopted by the airlines.
'Besides, pollution also results from road transport going in and out of the airport due to the rising flight movements, and this is not taken into account.'
Rising building and materials costs are another big issue for the project.
They are the main reason the costs of nearly all public works projects have surged by 40 to 100 per cent in the past four years.
There are also legal challenges - such as a court battle that has added eight months and HK$6.5 billion to the bill for the Hong Kong-Zhuhai-Macau bridge.
The authority says the third runway will bring in HK$912 billion in economic benefits in the 50 years to 2061, and that it is essential to cope with growth in air passenger and cargo traffic, which are expected to double from the present levels by 2030.
The number of flights per hour that the airport's two runways are capable of handling currently. It will rise to 68 an hour by 2015