The Federal Aviation Administration said Friday that it was seeking to penalize Boeing $5.4 million over allegations that it wrongly told the agency that defective wing parts were safe to use on its 737 Max jets.
The proposed penalty is on top of a $3.9 million penalty the agency issued in December over the same issue in older generation 737s.
The parts are called "slat tracks" and are used to guide parts of the wing that help the plane take off and land.
The FAA accused Boeing of doing too little to oversee its suppliers and then submitting aircraft to the agency for final safety approvals despite determining that the parts had failed a strength test. The problem affected 178 Max jets, the FAA said.
Boeing has 30 days to review the new fine.
The proposed penalty comes as Boeing faces ongoing scrutiny over the development of the Max, which was involved in two deadly crashes in a span of five months between 2018 and early 2019 that killed 346 people. The plane was grounded shortly after the second crash and is still under safety review by American and international regulators.
Boeing did not immediately respond to a request for comment on the new proposed penalty. In a statement issued after the first one, the company said any affected Max planes would be reviewed before the plane is cleared to fly again.
Boeing also said it has "not been informed of any in-service issues related to the slat tracks themselves."
The lengthy safety review after the crashes led to the ouster of Boeing chief executive Dennis Muilenburg last month and prompted the company to announce that it would halt production of the Max.
Boeing came under renewed criticism this week after it disclosed internal emails late Thursday that showed employees disparaging regulators and striving to minimize training requirements for the Max.
The FAA has also faced questions over its relationship with Boeing, with some lawmakers accusing the agency of being excessively cozy with the company. But in recent months, the agency has sought to demonstrate that it is using its powers to hold Boeing accountable, including by proposing the first fine in December.
Boeing also had 30 days to review that penalty, and the company and the FAA didn't immediately respond to a request for comment about the outcome of that review.
At a congressional hearing in December, a former Boeing manufacturing manager testified that factory workers faced extraordinary pressure as the company sought to deliver the new Max to its customers. As Boeing pushed to make more planes each month, the former manager said the result was a "factory in chaos."
Democratic lawmakers have accused the company of putting its financial ambitions ahead of safety, but the company said there was no indication any manufacturing issues contributed to the two crashes.
Also Friday, the FAA said it was proposing to levy a $3.92 million fine against Southwest Airlines, alleging that the company had incorrectly calculated weight and balance information on more than 21,000 flights.
That information is used to determine how the plane should be loaded, the FAA said, including how many passengers and fuel can be carried and where cargo should be put.
In a statement, Southwest said the problem occurred when the airline was transferring data from one computer system to another in the spring of 2018 and that it had since strengthened its process for managing the information.
"Southwest Airlines will continue working with the FAA to demonstrate the effectiveness of our controls and processes and seek to achieve an effective and appropriate resolution to this proposed penalty," the company's statement read in part.