WASHINGTON — The US Federal Aviation Administration said on Sunday some Boeing Co 737 MAX and NG planes may have parts that were improperly manufactured and that it will require their replacement, the latest issue to hit the world’s largest plane maker.

The FAA said up to 148 leading edge slat tracks manufactured by a Boeing sub-tier supplier are affected and cover 133 NG and 179 MAX aircraft worldwide. The FAA said a complete failure of a leading edge slat track would not result in the loss of the aircraft, but a failed part could cause aircraft damage in flight.

Slats are movable panels that extend along the front of the wing during takeoffs and landings to provide additional lift. The tracks are built into the wing.

The 737 MAX was grounded globally in March following a fatal Ethiopian Airlines crash after a similar Lion Air disaster in Indonesia in October. The two crashes together killed 346 people.

Chicago-based Boeing has yet to submit a software upgrade to the FAA as it works to get approval to end the grounding of the 737 MAX. Boeing did not immediately comment on Sunday.

The FAA said Boeing has identified groups of both 737 NG and 737 MAX airplane serial numbers on which these suspect parts may have been installed, including 32 NG and 33 MAX in the United States. The affected parts “may be susceptible to premature failure or cracks resulting from the improper manufacturing process,” the FAA said.

The FAA will issue an Airworthiness Directive to require Boeing’s service actions to identify and remove the parts from service, and operators will be required to perform this action within 10 days.

An FAA spokesman said the issue should not delay Boeing’s planned submission of a software update and training revisions, but it is still not clear when that will be submitted.

The FAA has said it has no timetable for ending the grounding of the airplane, while Boeing said last month it had completed its software upgrade but was still working to address information requests from the FAA before it can schedule a certification test flight and submit final certification documentation.

Acting FAA Administrator Dan Elwell told reporters on May 23 in Texas after a meeting with more than 30 international air regulators that the agency had not decided yet on training requirements.