Boeing is conducting the first test flight of a 737 MAX, according to flight tracking data, following the grounding of the plane last year after two crashes.
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The Federal Aviation Authority (FAA) over the weekend had cleared the US airplane maker to carry out certification test flights.
The clearance came after Boeing submitted safety fixes to the FAA, the regulator for review.
The flight took off from an airfield near Seattle.
The 737 MAX series of planes was grounded last year, following the deaths of 346 people in two accidents, one in October 2018 and another in March 2019.