The US Federal Aviation Administration said on Sunday that some of the parts used on Boeing Co 737 MAX and NG planes may have been improperly manufactured.

The US Federal Aviation Administration said that up to 148 leading edge slat tracks made by a Boeing sub-tier supplier may have been improperly manufactured, which covers 133 NG and 179 MAX aircraft worldwide. The FAA said that it will require their replacement.

The FAA noted that a complete failure of a leading edge slat track would not result in the loss of the aircraft, but warned that it could lead to aircraft damage in flight. 

Boeing 737 MAX was grounded after two planes of this type crashed within six months of each other — the first in Indonesia in October 2018 and the second in Ethiopia in March. The investigations into the incidents are underway, but numerous reports suggest the aircraft's Manoeuvring Characteristics Augmentation System was the reason for the crashes.

According to reports earlier this month, Boeing's global fleet of 737 MAX aircraft could remain grounded for at least another two months. The Wall Street Journal reported in May citing International Air Transport Association (IATA) Director General Alexandre de Junica that the impact of the grounding on the airlines was significant, though the IATA does not yet have any numbers to quantify the financial hit from cancelled flights and lower sales.