Trump said the decision was made out of an abundance of caution, citing new evidence found at this weekend's deadly crash site in Ethiopia.
An airline might fly its aircraft more hours each day, perhaps starting each day at 5 a.m. instead of 6, and flying until midnight instead of 11 a.m.
Questions have arisen over who should analyze the black box recorders from Sunday's crash: Ethiopian authorities reportedly don't want to turn the evidence over to the US, fearful there would be a conflict of interest in the analysis since the plane is American-made.
A number of countries, including the United Kingdom, had already barred the Boeing 737 Max 8 from its airspace.
Delta said that it does not operate any Boeing 737 MAX 8 or 9 aircraft.
"We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again", Boeing president and chief executive Dennis Muilenburg said.
"Pilots have been notified, airlines have been all notified", Trump said in making the announcement.
Affected passengers have the right to be rebooked on a future flight or request a refund, said Paul Hudson, president of consumer group FlyersRights.org, which pushed for the FAA to ground the 737 Max.
In a news conference in Ottawa Wednesday morning, delayed twice by what Garneau said was incoming new information, the minister called the decision to ground the plane a precautionary move that was made after a review of all the available evidence.
The Federal Aviation Administration held urgent meetings on Wednesday on the issue after Canada announced it become the last major country to ground the flight after two fatal crashes since October.
"There are delivery dates that aren't being met, there's usage of the aircraft that's not being met and all the supply chain things that Boeing so carefully crafted", Cox said. But a brand is at stake as well. The shares have fallen about 13 per cent since the crash, losing more than US$25 billion of market value.
Possibly presaging a raft of claims, Norwegian Air said it would seek recompense for lost revenue and extra costs after grounding its 737 MAX aircraft. The biggest impact could be on future deliveries given Boeing has almost 5,000 more 737 Max planes on order.
Four months earlier, the same model of aircraft operated by Lion Air crashed in Indonesia, killing all 189 people on board.
A spokesman for Ethiopian Airlines had said earlier that the black boxes recovered from the crashed plane would be sent to Germany for analysis.
Documents reveal that pilots flying last November reported engaging autopilot only for the aircraft's nose to pitch lower, prompting the warning system to exclaim: "Don't sink!"
Norwegian is expected to take delivery of dozens more of the "MAX" in coming years, raising the overall number to more than 70 by year-end 2021, according to recent company announcements.
The system continues to repeat the process if the computer detects the plane is still tilted at a too-high angle.
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