SINGAPORE - Singapore has temporarily suspended the operation of all variants of the Boeing 737 Max aircraft - the first country to do so - following two fatal accidents involving the aircraft in less than five months.

The ban, with effect from 2pm on Tuesday (March 12), affects Singapore Airlines' regional arm, SilkAir, which has six of the jets, and four other airlines that operate the B-737 Max to Singapore. These are China Southern Airlines, Garuda Indonesia, Shandong Airlines and Thai Lion Air.

The announcement by the Civil Aviation Authority of Singapore (CAAS), first reported by The Straits Times, comes after a B-737 Max 8 crashed in Ethiopia on Sunday, killing all 157 people on board.

CAAS is working with Changi Airport Group and the affected airlines to minimise any impact of the suspension on travellers.

Australia also imposed a similar ban on the operation of all variants of the B-737 Max aircraft, while Malaysia specifically banned Max 8 jets, which have also been grounded by airlines in China and Indonesia. The UK issued a safety directive suspending the use of the Max 8 and Max 9 variants in its airspace.

SilkAir operated its last B-737 Max 8 flight from Kathmandu, Nepal, which landed at Changi Airport at around 5.30am on Tuesday.

It is among more than 20 airlines that have grounded their B-737 Max 8 jets since Sunday's crash. South Korea and India have begun a special inspection of the aircraft.

The Ethiopian Airlines crash came on the heels of last October's Lion Air crash that killed all 189 people on board the same type of aircraft.

CAAS said it is suspending the aircraft flying into and out of Singapore to allow the authorities to review the safety risks associated with the plane. The regulator is in touch with the United States Federal Aviation Administration (FAA) as well as Boeing, and will review the suspension as relevant safety information becomes available.

The FAA maintains that the aircraft is airworthy but said it will mandate US carriers to install a software enhancement for the aircraft no later than next month.

Boeing said it has been working closely with the FAA on the development, planning and certification of the software enhancement, and it will be deployed across the 737 Max fleet "in the coming weeks".

The plane-maker is also expected to update its training requirements and flight crew manuals to reflect the changes.

While about a quarter of the close to 400 B-737 Max 8 jets now operating have been hit by suspensions, many carriers are continuing to fly the plane. They include two of its biggest operators: US carrier Southwest Airlines and Europe's Ryanair.

Mr Michael Daniel, a retired air crash investigator who now runs his own consultancy, said conflicting actions by countries, regulators and airlines, are confusing for air travellers. For example, while US carriers fly the plane, pilot and cabin crew unions have come out to say that staff should not be forced to serve on B-737 Max 8 flights.

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Associate Professor Lawrence Loh, director of the Centre for Governance, Institutions and Organisations at National University of Singapore Business School, said: "While it is fair to let the investigations take their course, we should be more conservative in terms of passenger safety, which is paramount.

"Even if there is no regulatory action, passengers ultimately vote with their feet and will walk away from all Boeing 737 Max flights if they do not have the confidence in the plane's safety."