Boeing faces new questions on the development of its latest big plane.

Boeing has suffered a setback in its effort to win regulatory approval for the 777X, a large jet designed for long-range flights. After nine months of deliberations, the FAA said in a May 13 letter to Boeing that it was unconvinced that the company was ready to move ahead with “type inspection authorization.” Securing that authorization signifies that a plane is about three-fourths of the way to being certified and is necessary to move forward in that process. The FAA said that it would need to commit more agency resources to certifying the plane, that Boeing might need to conduct more test flights and that the 777X was unlikely to be certified before late 2023. Originally scheduled to enter service in 2020, the 777X has been delayed many times. Boeing’s CE said earlier this year that he did not expect certification until late 2023. “Boeing remains fully focused on safety as our highest priority throughout 777X development,” the company said. “As we subject the airplane to a comprehensive test program to demonstrate its safety and reliability, we are working through a rigorous development process to ensure we meet all applicable requirements.” News of the letter, reported Sunday by The Seattle Times, comes as Boeing struggles to overcome problems on several fronts. <br/>