CHICAGO, July 26 (Xinhua) -- The U.S. Federal Aviation Administration (FAA) is proposing a 2.75-million-U.S. -dollar civil penalty against Boeing Co.'s commercial airplanes unit for allegedly failing to maintain its quality control system in accordance with approved FAA procedures, according to a file released Friday by the Administration.

The FAA says that in September 2008, Boeing discovered it had been installing nonconforming fasteners on its model 777 airplanes. The FAA sent a letter of investigation into the issue the next month.

The FAA alleges that Boeing repeatedly submitted action plans that set deadlines for the accomplishment of certain corrective actions, but subsequently failed to implement those plans.

The company implemented a plan to address the fastener issue on Nov. 10, 2010, more than two years after Boeing first learned of the problem.

Boeing stopped using the nonconforming fasteners after officials discovered the problem. However, some of the underlying manufacturing issues continued to exist until after the corrective action plan was in place.

Boeing has 30 days from the receipt of the FAA's civil penalty letter to respond to the agency.