The Federal Aviation Administration said Sunday that over 300 of Boeing’s 737 aircraft could have faulty parts on their wings. The issue would affect both MAX and NG—or Next Generation—jets, the MAX’s predecessor, and is due to a possible manufacturing flaw in their “leading edge slat tracks,” which guide the panels used on the wing during takeoffs and landings to provide additional lift. Boeing 737 MAX airplanes have been grounded worldwide following the fatal crash of an Ethiopian Airlines jet in March, less than five months after Indonesia’s Lion Air crash in October of last year. The two crashes killed everyone on board, a total of 346 people.