Boeing Co
The resumption of flights, which the planemaker said was backed by air safety regulators, is good news for Boeing and engine-maker CFM International, a joint venture between General Electric Co
CFM had said flaws in the forging of a disc inside the engine could have led to cracks.
Boeing grounded the fleet late last week, and announced it on Wednesday, just days before it planned to deliver its first 737 MAX 8 to an airline.
Inability to fly the plane could have threatened Boeing's ability to deliver the new jetliners on time.
The company said a 737 MAX 8 took off around 12:15 pm Pacific Time on Friday.
Boeing spokesman Doug Alder said regulators supported the resumption of flights.
"Our plan remains to start deliveries this month," he said, noting the flights are with planes that do not have the suspect discs.
Alder declined to say when the inspection and possible repair of any engines with the suspect discs would be complete.
The engines, known as the LEAP-1B, were being shipped back to plants in Lafayette, Indiana, and Villeroche, France, for inspection.
Safran Aircraft Engines Chief Executive Olivier Andries told reporters on Thursday that the company hoped to fix the problem "within a few weeks."
Alder also declined to estimate the potential cost, or say whether any faulty discs had been found so far.
The problem stemmed from a forging issue noticed on low-pressure turbine discs after they were sent to CFM from a supplier. A second supplier had stepped up production, CFM said.
Andries said on Thursday that CFM still hoped to deliver as many as 500 LEAP engines this year, including variants used by Airbus And China's COMAC.