WASHINGTON — WASHINGTON — - The Federal Aviation Administration on Wednesday proposed levying multimillion-dollar fines against United Airlines and US Airways for safety violations, including flying a plane after mechanics stuffed shop towels into an engine.

The agency said that it has proposed a $5.4 million fine against US Airways of Tempe, Ariz., for operating eight planes on a total of 1,647 flights from October 2008 to January 2009 in violation of safety directives or the company's own maintenance rules.

The agency also said it is proposing a $3.8 million fine against United of Chicago for operating one of its Boeing 737 aircraft on more than 200 flights with shop towels covering openings near where oil collects in the bottom of the engine instead of using protective caps required by the carrier's maintenance procedures.

Under FAA rules, the airlines have 30 days to present mitigating evidence before the agency may impose the fines.