US federal aviation authorities said Monday they will order Boeing to modify its 737 MAX 8 aircraft, including anti-stalling software and maneuvering system updates, after two of the planes crashed in five months.

Meanwhile, Singapore became the latest country to ban the use of the aircraft in its airspace. The city state announced the ban on Tuesday morning.

The Federal Aviation Administration (FAA) told international civil aviation authorities that it “anticipates mandating these design changes… no later than April,” although it did not ground the fleet.

“The FAA continuously assesses and oversees the safety performance of US commercial aircraft,” it said.

“If we identify an issue that affects safety, the FAA will take immediate and appropriate action.”

The FAA has notified other global civil aviation authorities that it may soon share safety information concerning Boeing’s 737 MAX 8, the statement said.

Boeing is also set to update its training requirements and flight crew manuals to reflect the changes.

One of the aircraft, operating as Ethiopian Airlines Flight ET302, crashed Sunday southeast of Addis Ababa shortly after takeoff, killing all 157 passengers and crew members aboard.

The same model – a more fuel-efficient version of the 737 – crashed in late October in Indonesia during a flight operated by Lion Air, leaving 189 people dead, also just moments after takeoff.

It is extremely rare for a new aircraft model to be involved in two deadly incidents over such a short period of time. While both crashes are still under investigation, there is no evidence of a connection between the two.

An FAA team is currently in Ethiopia participating in a probe into the latest crash with investigators from the US National Transportation Safety Board (NTSB).

The cause of the crash has not yet been determined. However, the digital flight data recorder and cockpit voice recorder have been recovered, Ethiopian Airlines said in a Twitter post Monday morning.

“We are collecting data and keeping in contact with international civil aviation authorities as information becomes available. Today, the FAA will issue a Continued Airworthiness Notification to the International Community (CANIC) for Boeing 737 MAX operators,” the FAA said in a statement. “The FAA continuously assesses and oversees the safety performance of U.S. commercial [aircraft]. If we identify an issue that affects safety, the FAA will take immediate and appropriate action.”

The Boeing aircraft involved in Sunday’s deadly crash had been delivered to Ethiopian Airlines in November, had flown 1,200 hours and was last maintained in early February, according to Ethiopian Airlines group CEO Tewolde Gebremariam, Yahoo Finance reported.

Grounding flights

Airlines in Ethiopia, Indonesia and China grounded their Boeing 737 Max 8 fleets on Monday as concern over the safety of one of Boeing’s newest aircraft mounted.

“Given that two accidents both involved newly delivered Boeing 737-8 planes and happened during take-off phase, they have some degree of similarity,” the Civil Aviation Administration of China (CAAC) said in a statement. Chinese airlines comprise more than one-quarter of the global fleet of the Boeing 737-8 aircraft, according to Reuters.

Other countries have telegraphed that they are taking extra precautions in the wake of the deadly crash. Cayman Airways announced that it was temporarily grounding its two Boeing 737 Max 8 aircrafts, effective Monday, until more information is received on the investigations. Turkish state-run carrier Turkish Airlines is in talks with Boeing and is following the developments of the investigations, CEO Bilal Eksi wrote in a Twitter post Monday. South Korea is carrying out a special investigation of the aircraft after the carrier Eastar Jet became the first in the country to take delivery of a Boeing 737 Max 8. India’s Directorate General of Civil Aviation said on Monday it will issue safe instructions Monday or Tuesday for Indian carriers operating the aircraft.

The Canadian authorities believe it is simply too soon to say what caused the brand-new Ethiopian airliner to crash – and until investigators can pinpoint what caused the deadly incident, dozens of Boeing 737 Max 8 planes will be free to fly in Canada, CBC News reported. Transport Minister Marc Garneau said it would be “premature” to ground all 41 of those planes currently owned by Canadian air carriers. The Air Canada Pilots Association sent out a statement urging Transport Canada “to take proactive action to ensure the safety of the Canadian traveling public.”

Boeing (BA) shares declined Monday after the crash.

– Additional reporting by Agence France-Presse