US President Donald Trump on Wednesday announced an emergency order from the Federal Aviation Administration grounding Boeing's 737 MAX jets, following the action of 42 other countries that halted flights of the aircraft after crashes in Ethiopia and Indonesia killed all aboard.

"All those planes are grounded, effective immediately," Trump told reporters at the White House during a scheduled briefing on border security.

The president said any plane in the air would complete its scheduled flight and would then be grounded. He added that all affected airlines had been notified of his action.

Trump said he decided to ground the aircraft after meeting with Transportation Secretary Elaine Chao.

He said the decision to ground the MAX 8 and MAX 9 was made because of new information about Sunday's crash in Ethiopia, which killed 157 people. The Federal Aviation Administration (FAA) said new evidence had been collected at the sight of the crash on Wednesday, and that information — along with new satellite data — led to the grounding decision.

Until Wednesday afternoon, the FAA said there was insufficient evidence to halt flights of the aircraft despite calls from US lawmakers and airline labor unions to suspend flights until an investigation could be completed and after more than 40 other countries had grounded the aircraft.

Trump said his move was more precautionary than mandatory.

"I didn't want to take any chances. We didn't have to make this decision today," he said. "We could have delayed it. We maybe didn't have to make it at all. But I felt it was important both psychologically and in a lot of other ways."

Trump said his decision was fact-based, even as he acknowledged it was made partly with regard for the mental well-being of American travelers.

"The safety of the American people, of all people, is our paramount concern," Trump told reporters.

Boeing CEO Dennis Muilenburg said in a statement that the company had consulted federal authorities and recommend the temporary restriction to the FAA "out of an abundance of caution."

Safety concerns about the 737 MAX jets pounded Boeing's stock price on Monday and Tuesday, but in trading Wednesday on the New York Stock Exchange, the stock closed at $375.54 a share, up $0.13, or 0.04 percent from Tuesday's close. Boeing's market value has lost about $24 billion since safety issues were raised.

Prior to Trump's announcement, US airlines using the 737 MAX 8 — American Airlines and Southwest Airlines — stood by the aircraft and continued scheduled flights. United Airlines uses the MAX 9.

When Trump made his announcement, dozens of the planes operated by the three airlines were airborne.

American Airlines said in a statement to Business Insider that it had 24 aircraft affected by the directive and was "working to rebook customers as quickly as possible".

At least six American flights were canceled between New York's LaGuardia Airport and Miami. Southwest Airlines has the most MAX planes, 34. United Airlines, which operates 14 737 MAX 9's, said it would have to cancel 40 flights per day.

Trump made his announcement hours after Canada grounded MAX 8 and 9 planes registered in the country. Canadian Transport Minister Marc Garneau banned the plane's entry into Canadian airspace, shutting down US flights that use the aircraft. A total of 42 nations, including China, have grounded the plane, one of Boeing's top sellers.

Canada took the action after reviewing recently released satellite tracing data that suggested similarities between the Ethiopian Airlines crash that killed 157 people on Sunday and a Lion Air crash that killed 189 people last October, Garneau said at a press conference.

"This (data) is not conclusive, but it is something that points possibly in that direction, and at this point we feel that threshold has been crossed," he said. "It would be a mistake to say it looks exactly like the one that brought Lion Air down."

Garneau said the US had "absolutely not" pressured Canada to avoid grounding the aircraft.

There is no solid evidence linking the crash of an Ethiopian Airlines jet and the crash Indonesian Lion Air flight, but there are broad similarities.

The new Boeing 737 MAX 8 was used on both flights. Both pilots reported control issues after takeoff, suggesting the problem was onboard rather than an external factor such as birds being sucked into the engines or extensive damage to the aircraft. The pilots requested and received permission to return to the airport. Both planes crashed before landing.

The similarities led the European Aviation Safety Agency to bar all Boeing 737 MAX aircraft from the airspace of its 32 member countries, effectively grounding the plane.

The preliminary cause of the crashes won't be known until investigators analyze the onboard flight data recorders and communication between the pilots and the control tower. Ethiopian Airlines said Wednesday it will send the black boxes to Europe for analysis.

Following the Indonesian crash, investigators focused attention on the aircraft's anti-stall system that automatically points the nose of the plane down and may cause a plane to rapidly descend. Pilots may not have been notified about the problematic software, but shutting off the anti-stall system and flying manually should be able to correct an unwanted descent, flight instructors said. Radar tracks of both planes showed erratic flying prior to the crash.

On Tuesday, The Associated Press reported that two pilots said the nose of their plane tilted down after engaging the autopilot on Boeing 737 Max 7 planes. In both cases, the pilots shut off the autopilot and quickly recovered. The problems are similar to the suspected cause of the crashes in Indonesia and Ethiopia.

Prior to the crash in Ethiopia, Boeing said it would make a major software change to the 737 MAX 8 aircraft flight control system. The new software will enable the plane's stall prevention system to use multiple data feeds rather than relying on the single sensor used since the aircraft was first delivered in 2017.

US regulators are expected to require installation of the new software, which will take about an hour, by the end of April. Basic aircraft design calls for multiple systems, called redundancy, so there can be no single point of failure, but it is not known if the anti-stall system was a factor in either crash.

Boeing's 737 MAX is the latest update of its popular, single-aisle, twin-engine aircraft. Boeing has about 5,000 planes on back order ,selling at about $120 million each. The fuel-efficient plane has a range of 3,215 to 3,825 miles (about 5,954 to 7,084 kilometers). The aircraft is offered in four lengths and seats 138 to 230 passengers.

Following concerns about the aircraft's safety, India said it would not take deliveries of 737 MAX jets. Ethiopian Airlines said it may cancel its order for additional planes. Norwegian Air said it expects Boeing to pay for lost revenue following grounding of the planes.

The similarities in the crash of the Ethiopian and Indonesian flights have spooked some US passengers who ask to be booked on flights using a different type of aircraft. Kayak.com, a website that allows users to shop for the cheapest flights, said it had modified its search parameters to allow users to exclude certain types of aircraft.

Contact the writer at scottreeves@chinadailyusa.com