The planes have been grounded since March 2019, after the second fatal crash.

Boeing spokesman Gordon Johndroe said on Monday that "although Mr. Pierson did not provide specific information or detail about any particular defect or quality issue, Boeing took his concerns about 737 production disruption seriously."

Boeing did not immediately respond to a request for comment. The company has 30 days to respond to the FAA.

According to federal court records, more than 50 lawsuits were filed against Boeing by families of passengers on the Lion Air Max that crashed Oct. 29, 2018, and about 100 lawsuits were filed relating to the crash of an Ethiopian Airlines Max on March 10.

American Airlines and Southwest Airlines said Friday they were pushing back the resumption of flights because of the 737 MAX grounding until early March.

The Federal Aviation Administration has spent months reviewing Boeing's proposed software upgrades to a key safety system and other training and system changes but is not expected to allow the plane to return to service until December at the earliest.

FAA and Boeing representatives briefed members of the International Civil Aviation Organization's governing council in Montreal on Thursday on efforts to return the plane to service.

Acting FAA Administrator Daniel Elwell said the strategy has “consistently produced safe aircraft designs for decades.”

Boeing said it will pay to train airline pilots on its 737 MAX aircraft.