Europe's aviation safety agency cleared a modified version of the Boeing 737 Max to return to skies after almost two years being grounded.
"We have every confidence that the aircraft is safe, which is the precondition for giving our approval," said Patrick Ky, the European Union Aviation Safety Agency executive director.
"But we will continue to monitor 737 MAX operations closely as the aircraft resumes service."
Ky said the decision was taken independently of both Boeing and the US Federal Aviation Administration. The European agency carried out their "own flight tests and simulator sessions", he added.
The UK aviation agency cleared the aircraft to fly again shortly after the European clearance.
"The international work to return the Boeing 737 MAX to the skies has been the most extensive project of this kind ever undertaken in civil aviation and shows how important the cooperation between states and regulators is to maintaining safety," said Richard Moriarty, the UK Civil Aviation Authority's chief executive.
The European aviation agency mandated "a package of software upgrades, electrical working rework, maintenance checks, operations manual updates and crew training which will allow the plane to fly safely in European skies."
The plane was grounded in March 2019 following two deadly crashes just five months apart. An October 2018 Lion Air plane crash and a March 2019 Ethiopian Airlines crash killed 346 people.
They determined that the cause of the crash was a design flaw in the flight control system called the Maneuvering Characteristics Augmentation System (MCAS).
The system would activate based on one sense, pushing the nose of the aircraft down.
"In both accidents, pilots finally lost control of their plane, resulting in a crash with total loss of aircraft," the European agency said.
The aircraft was cleared to fly in US skies late last year, flying its first passenger flight in December.