"Audit has recommended that the director general of Civil Aviation should take measures to ensure that timely approval is sought from FSTB for procuring equipment in accordance with the requirements laid down," the report said.

In 2008, the Legislative Council approved funding of HK$1.9 billion to the CAD for the headquarters. The project was awarded to a contractor in 2009. The audit watchdog said that under the terms of the deal, the government was contractually bound to acquire the specified security and electronic systems at the tender price of HK$67.45 million.

"However, the CAD did not seek the [Financial Services and the Treasury Bureau's] approval for the purchase of such systems until February 2011," the report said.

Meanwhile, in 2007, the report said the CAD received approval for the headquarters with a net operational floor area of 22,775 square metres, of which 3,240 square metres was reserved for future expansion.

But the watchdog found that an area of 1,500 square metres built at the new headquarters was not approved. The new headquarters came into use in December 2012.

In another report, the watchdog said that the CAD's new air traffic control system, which cost HK$1.56 billion, was supposed to be in use this year. But it will only be ready next year as many tests had still not been completed.

The CAD earlier told Legco that its existing system should have ended its usable life in 2012. But from January to June this year it was still in use and working beyond its planned capacity 67 per cent of the time.

In addition, a HK$101.4 million precision runway radar was purchased and put to use in 2000. The Audit Commission found that even before funding approval was sought, the CAD was already aware of the constraints by two consultancy studies.

The radar was eventually used for only about four years.

The director general of the CAD agreed with all the recommendations put forward in the report.