Brazilian airline Gol said it would become the first company on Wednesday to resume commercial flights with the Boeing 737 MAX, nearly 21 months after the plane was grounded worldwide following two deadly crashes. "For the past 20 months, we have been carrying out the most intensive safety review in the history of commercial aviation," Gol's vice president for operations, Celso Ferrer, said in a statement. "Safety comes first and foremost." Gol, the biggest domestic airline in Brazil, said 140 of its pilots had undergone training on the newly overhauled jet in the United States. The company said it expected to have its full fleet of seven 737 MAX planes back in the air by the end of the year. Gol did not immediately respond to a request for further information. Brazilian news site UOL cited the company's chief executive, Paulo Kakinoff, as saying that any passenger who did not feel comfortable flying on the 737 MAX would be allowed to reschedule the flight any time at no cost. The MAX was grounded in March 2019 after two crashes that together killed 346 people. The fallout of the 2018 Lion Air and 2019 Ethiopian Airlines crashes plunged Boeing into crisis -- made worse for the US aerospace giant by the upheaval the coronavirus pandemic has brought for the travel industry. Investigations identified a principal cause of both crashes as a faulty flight handling system. Meant to keep the plane from stalling as it ascended, the automated system instead forced the nose of the plane downward. The US Federal Aviation Administration (FAA) ordered Boeing to overhaul the system and implement new pilot training protocols. Last month, it approved the plane to return to service after the upgrades were put in place. Brazil's National Civil Aviation Agency (ANAC) followed suit on November 25. They are the only two aviation regulators to green-light the plane so far. The European Aviation Safety Agency (EASA) began the process of recertifying it last month. In the US, American Airlines is expected to become the first company to resume commercial service with the 737 MAX, with a flight scheduled for December 29. jhb/ft