From its inception, Boeing’s 737 Max was designed to save airlines the expense of training their pilots on flight simulators. During the initial approval of the plane and after two crashes killed 346 people last year, Boeing argued in conversations with the Federal Aviation Administration that simulator training was not necessary.

Now, after a worldwide grounding has cost the company billions of dollars over nearly 10 months and caused it to temporarily halt the production of the Max, Boeing has reversed course. On Tuesday, the company said it would recommend that pilots train in flight simulators before flying the Max.

The decision stems from Boeing’s analysis of recent flight simulator tests that were part of the work necessary to return the Max to service, which showed that pilots were not using the right procedures to handle emergencies. Those tests are the latest hurdle for Boeing, which has encountered setback after setback as it tries to fix problems with the Max and persuade regulators that the plane is ready to fly.

The Max has been grounded since March, and Boeing has been working for months on changes to the software that contributed to both accidents. Boeing, the largest aerospace manufacturer in the world and one of the most important companies in the United States, has been roiled by the Max grounding, which still has no end in sight. Last month, the company’s board ousted its chief executive, Dennis A. Muilenburg, who had presided over a deteriorating relationship with the F.A.A. and key airline customers.