Malaysia wants to take back in stages control of its airspace over southern Johor that has been delegated to Singapore, Malaysian Prime Minister Mahathir Mohamad said yesterday.

It aims to do so beginning from the end of this year to 2023, he added.

Speaking to reporters at a news conference with Prime Minister Lee Hsien Loong after their Leaders' Retreat at his office complex, Tun Dr Mahathir noted that the high-level committee formed to review the airspace arrangement between both countries has begun discussions.

Referring to the letter of agreement inked by both countries in 1974 on this arrangement, Dr Mahathir said it was signed at a time when the Kuala Lumpur Flight Information Region (FIR) was in its infancy and air navigation facilities in Malaysia were not adequate.

The International Civil Aviation Organisation (ICAO) had at the time recommended that air traffic services in the area concerned be delegated to Singapore, he noted.

"We have made significant investments in preparation to take back the said delegated airspace and hope that this can be done expeditiously," Dr Mahathir said.

Singapore is ready to discuss this matter with Malaysia, PM Lee said at the news conference.

"The key considerations are the safety and efficiency of air traffic operations, and the needs and interests of both countries," he added.

"I told Dr Mahathir this is a complex matter that will involve consulting many stakeholders, including airlines and ICAO, and cannot be rushed," PM Lee said.

He noted that civil aviation is growing rapidly for both countries, and the Kuala Lumpur International Airport (KLIA) and Changi Airport are now major regional airports. KLIA has greater capacity to grow than Changi, he said. "Because Changi is building a third runway and I think that is the limit, whereas KLIA already has three runways and has space to build five."

It is therefore in both countries' interests that this growth be facilitated and take place safely, PM Lee said.

In an interview with Singapore media yesterday afternoon to wrap up his visit to Malaysia for the Leaders' Retreat, PM Lee said there is opportunity for both countries to cooperate, pointing to how the expansion of civil aviation and passenger traffic in Asean has been of tremendous benefit to the whole region.

"So, you need to work together in order to realise that and unless we can provide a system which is safe, efficient and which will meet the needs of the commercial operators, I think all sides will be losers."

Asked what implications the review would have for Singapore, PM Lee noted that Malaysia's airspace over southern Johor was delegated to Singapore in 1974 after an ICAO meeting the year before.

Singapore will talk to Malaysia and see what adjustments are possible, PM Lee said.

"I think it is not reasonable for us to say we will not talk or we will not listen to your concerns. We have to do that," he said.

"Ministers on both sides understand the parameters, and it has to be done with a view to safety and efficiency of civil aviation - that is a key objective," he added, noting that the talks "will take some time".

Both governments had also taken steps to resolve the dispute over landing procedures at Seletar Airport ahead of the retreat.

On Monday, Transport Minister Khaw Boon Wan said that the civil aviation authorities of both countries are developing Global Positioning System (GPS)-based instrument approach procedures for Seletar. The new procedures will replace the Instrument Landing System (ILS) procedure that Singapore has withdrawn.

PM Lee noted: "We have unwound the impasse. But the desire to have an instrument system for Seletar is a reasonable one, and if not by the ILS, you can use the GPS system, which also enables you to land with instrument and not only in good weather using our eyeballs."

Malaysia, meanwhile, has indefinitely suspended its permanent restricted area over Pasir Gudang.

The agreement paves the way for Malaysian carrier Firefly to begin flying into Seletar on April 21, more than four months after its flights to Singapore were suspended.

In a Facebook post last night, Foreign Minister Vivian Balakrishnan said he is glad that Firefly will now be able to fly to Seletar, and that Malaysian Transport Minister Anthony Loke has said he will be on the first flight.

"There are still many complex airspace issues that the transport authorities will have to discuss in the months and years ahead," Dr Balakrishnan added.