The aircraft that will now be investigated are various versions of the 737 Max model. The FAA estimates that a total of 471 aircraft are involved.
The agency said in November that it had received reports of cracks in a front reinforcement plate on several older 737 NG aircraft.
The Max model has a similar design and manufacturing process to the older models, “making these airplanes susceptible to the same cracking problems,” the FAA wrote at the time.
Boeing 737 Max models were involved in two fatal crashes in 2018 and 2019, killing a total of 346 people. Boeing's Max planes have been grounded for several periods.
