The Federal Aviation Administration (FAA) is proposing a $3.8 million civil penalty against United Airlines. The government claims the carrier operated one of its Boeing 737 aircraft on more than 200 flights after United had violated its own maintenance procedures on one of the plane's engines.

On April 28, 2008, a United 737 returned to Denver after shutting down an engine due to low oil pressure indications. A week later, United mechanics found that two shop towels, instead of required protective caps, had been used to cover openings in the oil sump area where maintenance had been performed in 2007. As a result, the plane flew more than 200 times when it was not in "airworthy condition," according to the FAA.

The agency says that United's maintenance procedures specifically require use of protective caps or covers on all components that could be affected by entry of foreign materials.