SINGAPORE - A group of People's Liberation Army Air Force (PLAAF) aircraft that flew into Singapore's Flight Information Region (FIR) in May was not deemed to have posed an aerial threat to Singapore, said Defence Minister Ng Eng Hen.

The Civil Aviation Authority of Singapore (CAAS) - the appointed authority to manage Singapore's FIR - did not receive any flight plans from the PLAAF, nor did CAAS communicate with it nor any of its aircraft, he said in Parliament on Tuesday (July 6).

However, state aircraft, which includes military aircraft, are not required to do so, as long as they fly with regard for the safety of other aircraft, he said.

Dr Ng was responding to questions from Mr Gerald Giam (Aljunied GRC) and Mr Dennis Tan (Hougang).

On June 1, the Royal Malaysian Air Force said a formation of 16 transport aircraft from the PLAAF had approached the coastline of Sarawak in east Malaysia on May 31. The Chinese planes had first passed through the FIR administered by Singapore, then that of Malaysia.

China had said that the PLAAF was conducting routine flight training and exercising "freedom of overflight in the relevant airspace".

Mr Giam asked, among other things, whether the Republic of Singapore Air Force (RSAF) had tracked the flight of the 16 PLAAF aircraft and was successful in establishing communication with them.

Mr Tan asked for the Government's assessment of the flight over waters that are disputed by China and Malaysia.

Dr Ng said the questions asked by the MPs "conflate a number of issues that may inadvertently give rise to misinterpretations and misunderstandings unless they are clearly distinguished".

He then said he would address three separate but related issues.

First, Singapore respects the right of military aircraft and ships to conduct passage and training over areas and waters in line with international law, including the 1982 United Nations Convention on the Law of the Sea, Dr Ng said.

This is the basis for the flights and training RSAF conducts, as well as for the conduct of bilateral or multilateral exercises in the South China Sea, he added.

This includes exercises such as Commando Sling and Cooperation Afloat Readiness and Training, or Carat, with the United States.

Second, the International Civil Aviation Organisation appoints a civilian authority to manage the airspace of each FIR, and this authority is designated as the air traffic services (ATS) authority.

Dr Ng said: "In this role, (the ATS authority) does not act as a watchdog over disputed areas, nor should that authority adopt a partisan role on behalf of any party, or for itself."

While state aircraft are not required to file flight plans with the ATS authority, Dr Ng said, there are some that do.

The RSAF routinely adopts this practice, mainly to assist the ATS authority in coordinating and deconflicting RSAF flights from civilian aircraft, as part of its responsibility for operating with due care, he said.

Third, Dr Ng said as Singapore is a small country with a high population density, and therefore more vulnerable to air threats, its armed forces maintain air defence units at high alert.

The RSAF conducts non-stop surveillance of Singapore's skies through both ground-based radars and aerial reconnaissance to detect unknown or suspicious aircraft that are close enough to pose a potential threat, he said.

On average, each year, the RSAF responds to more than 350 such incidents.

In a follow-up question, Mr Giam asked how Singapore ensures that state aircraft do not have hostile intent when entering its FIR, given that they are not required to file flight plans.

Dr Ng replied that there are a number of aspects, including the plane's movement, and whether flight plans have been filed.

He gave an example of how a private aircraft that had got lost, years ago, was guided to land in a safe area by an F-16 fighter jet.

"There have been other instances which RSAF must use its judgment, and there are strict protocols," he said.