The Federal Aviation Administration and President Donald Trump said more safety checks are needed on Boeing 737 Max planes.
The black boxes found at the scene of Sunday's deadly plane crash that killed 157 people in Ethiopia could give more insight into exactly what happened on board.
"They are in France now and we hope to start getting initial data feeds from the boxes. Hopefully by the end of the day," said Daniel Elwell, acting administrator of the FAA.
TIMELINE: Deadly Ethiopian Airlines plane crash
The FAA said their decision to ground all 737 Max planes was made after enhanced satellite data and physical evidence found similarities between the Ethiopian jet's movements and an Indonesian Lion Air flight that crashed back in October, killing 189 people.
"We don't know how long the planes will be grounded," Elwell said.
The FAA said the emergency order led to dozens of flight cancelations. American Airlines canceled nearly 100 flights and Southwest Airlines canceled more than two dozen.
Passengers flying in and out of Midway International Airport in Chicago, one of the largest hubs for the Boeing Max jets, said the grounded planes did not affect their plans on Thursday.
"Doesn't concern me because I feel whatever issues are out there, they will get them resolved," said Andy Lien, a traveler at Midway.
Some passengers said they will think twice about which planes they board in the future and hope the issues will be figured out soon.
"It definitely makes me check the plane, take a look at it. But at the end of the day, most people don't even know what type of plane they are flying on," said James Waymore, another traveler at Midway.