WASHINGTON ( CNN ) -- The Federal Aviation Administration on Wednesday proposed fines against two of the nation 's largest airlines , saying the airlines flew planes on hundreds of occasions in violation of FAA or airline safety standards . US Airways says the problems are in the past . United notes it self-reported its problem . The FAA is seeking a $ 5.4 million fine from US Airways and a $ 3.8 million fine from United Airlines for unrelated violations . Both airlines issued statements Wednesday assuring the public of their commitment to safety . US Airways blamed its problems on the difficulties of merging US Airways and America West maintenance operations in 2007 . United , meanwhile , said it self-reported the incident leading to its proposed fine and has since taken steps to ensure that safety standards are met . The US Airways case involved the greatest number of planes -- eight . The FAA alleges US Airways operated the eight aircraft on a total of 1,647 flights last fall and winter while the planes were in a potentially unsafe condition . Three of the planes were flown while not in compliance with FAA rules known as Airworthiness Directives , or ADs . The FAA issues ADs when it discovers a potentially unsafe condition on a type of aircraft , and it wants airlines to inspect their fleets or conduct preventive maintenance . The FAA said it issued an AD requiring airlines to inspect Airbus A320 aircraft for possible cracking of a landing gear part . But US Airways operated two Airbus A320s on a total of 43 flights without complying with the ordered inspection . The airline also operated an Embraer 190 aircraft on 19 flights without performing an inspection to prevent a cargo door from opening during flight , according to the FAA . The remaining five cases involve the airline 's failure to follow its own maintenance procedures , the FAA said . In a letter to its employees , US Airways Chief Operating Officer Robert Isom called the FAA announcement disappointing . `` It is important to remember that today 's announcement references situations that are in the past , and in several cases , date back to two years ago , '' he wrote . `` Our team has worked cooperatively with the FAA to investigate and correct any discrepancies to the FAA 's satisfaction . '' The United Airlines case involves one aircraft , a Boeing 737 . According to the FAA and the airline , a pilot noticed a low fuel pressure indication while on a flight from Denver , Colorado , on April 28 , 2008 . The pilot shut down an engine and returned to the Denver airport . United mechanics who inspected the engine found that two shop towels had been used to cover openings in the oil sump area , instead of protective caps . The FAA said the aircraft had flown more than 200 times in the unsafe condition before the problem was discovered . A United spokeswoman said the airline reported the incident to the FAA and has taken several measures to prevent a recurrence , including additional training of maintenance workers . Both airlines have 30 days to respond to the FAA 's proposal for fines . In March , Southwest Airlines agreed to pay $ 7.5 million to settle a complaint that it flew unsafe planes .
FAA seeks a $ 5.4 million fine from US Airways , $ 3.8 million fine from United Airlines . Airlines issue statements assuring public of their commitment to safety . US Airways case includes planes not complying with Airworthiness Directives . United plane flew with shop towels covering openings in oil sump area .