"If there is any doubt, then grounding is the only right decision," Carsten Spohr told a news conference.

The U.S. Federal Aviation Administration on Wednesday became the latest regulator to order the best-selling 737 MAX taken out of service, joining others awaiting word on whether the plane was safe to fly.

The Ethiopian Airlines jet crashed shortly after takeoff on Sunday, killing everyone on board, in the second such accident involving the model in less than five months.

Lufthansa, Germany's largest airline, does not fly the 737 MAX, nor has it ordered any of the aircraft. Boeing says it has delivered 376 of the aircraft out of more than 5,000 that have been ordered.

(Reporting by Ilona Wissenbach; Writing by Douglas Busvine; Editing by Thomas Seythal)