THE proposed new Airport Corporation Bill is meant to be an attempt to strike a sound balance between government control and commercial flexibility. According to the consultation paper put out yesterday, the Bill would give the Financial Secretary a big say in how the new body spent the billions of dollars of taxpayers' money invested in it. It would also give him the right to set the dividend it pays out to the Government as the sole shareholder. But, the paper says, the Government should not restrict the corporation's room to act in a prudently commercial way. To do so would be to restrict its ability to borrow and promote private sector investment in airport services, without forcing the Government to guarantee all the corporation's debts. This reasoning is sensible, as far as it goes. But while the Bill does leave the corporation ample room to manoeuvre, it falls short of its parallel aim of protecting and promoting the public interest. For all the powers given to the Financial Secretary, provision for independent public audit is still inadequate. The Director of Audit is only to be given access to the corporation's accounts in the event of serious Government concern. His role is to be confined to locking the stable door after the horse has run away, possibly with millions of dollars of public money in the saddle-bags. Instead of giving an active role to the Director of Audit, whose thorough reports would be made public and passed for scrutiny to the Legislative Council's Public Accounts Committee, it is proposed to continue with the less-open system of internal reporting used by the Provisional Airport Authority. Both the authority's in-house audit unit and an outside auditor report to an internal Audit Committee. Although the Audit Committee can also instigate value-for-money studies, any criticisms it makes are unlikely to be made public. If the Government believes the Audit Department cannot be trusted to examine commercial operations effectively, it should say so. It then should re-organise the department and retrain the staff to ensure it can do so in future. If, however, what the Government means by wishing ''to avoid undermining the ability of the corporation to act in a prudently commercial way'' is that it intends to prevent public scrutiny of the corporation's operations, it should think again. The corporation is to be given responsibility for billions of dollars of Government money. The way that money is spent is, and always will be, a matter of public concern.