Boeing has told suppliers it is delaying a key production milestone for its 737 MAX by six months, three industry sources said, in a sign the planemaker is struggling to boost production of its best-selling jet.

Boeing’s latest 737 supplier master schedule communicated to the industry calls for MAX output to reach 42 a month in March 2025, compared with a previous target of September 2024, the sources told Reuters.

While the so-called master schedule is a demand signal, it is not an official production target. Boeing has not changed its official plane production target, which calls for 38 MAX jets a month by the end of 2024, up from roughly 25 jets a month in July.