After nearly two years and a pair of deadly crashes, the United States Federal Aviation Administration has cleared Boeing's 737 Max for flight.
The nation's air safety agency announced the move today, saying it was done after a "comprehensive and methodical" 20-month review process.
Regulators around the world grounded the Max in March 2019, after the crash of an Ethiopian Airlines jet.
That happened less than five months after another Max flown by Indonesia's Lion Air plunged into the Java Sea.
A total of 346 passengers and crew members on both planes were killed.
Federal Aviation Administration chief Stephen Dickson signed an order today rescinding the grounding. US airlines will be able to fly the Max once Boeing updates critical software and computers on each plane and pilots receive training in flight simulators.
The FAA says the order was made in cooperation with air safety regulators worldwide.
The move follows exhaustive congressional hearings on the crashes that led to criticism of the FAA for lax oversight and Boeing for rushing to implement a new software system that put profits over safety and ultimately led to the firing of its CEO.
Investigators focused on anti-stall software that Boeing had devised to counter the plane's tendency to tilt nose-up because of the size and placement of the engines.
That software pushed the nose down repeatedly on both planes that crashed, overcoming the pilots' struggles to regain control. In each case, a single faulty sensor triggered the nose-down pitch.
The new software now requires inputs from two sensors in order to activate the software. Boeing says the software also does not override pilot controls like it did in the past.
The company changed the software so it doesn't repeatedly point the nose of the plane down to counteract possible aerodynamic stalling. Boeing also must change the way wires are routed to a tail stabiliser bar.
On CNBC, Dickson said the design and pilot training changes required by the FAA "makes it impossible for the airplanes to have the same kind of accident that unfortunately killed 346 people."
In an FAA video, Dickson said that for the time being, the FAA will inspect every new Max before letting the planes fly.
Nearly 400 Max jets were in service worldwide when they were grounded, and Boeing has built and stored about 450 more since then. All have to undergo maintenance before they can fly.
Pilots must also undergo simulator training, which was not required when the aircraft was introduced.
Relatives of people who died in the crashes aren't convinced the Max is safe. They accused Boeing of hiding critical design features from the FAA.
"The flying public should avoid the Max," said Michael Stumo, whose 24-year-old daughter died in the second crash. "Change your flight. This is still a more dangerous aircraft than other modern planes."
Europe's aviation regulator, the European Union Aviation Safety Agency, said it will take public comment on plans to clear the Max for flight and expects to finalise a plan by early next year. Some EU states will have to lift their own grounding notices as well. Regulators in Canada and China are still doing their own reviews.