United Airlines is facing a fine of $435,000 from the Federal Aviation Administration, which said Tuesday that the airline flew a Boeing 787 passenger airplane that was potentially unsafe nearly two dozen times on domestic and international flights in 2014.
A statement from the federal agency said that United mechanics replaced a fuel pump pressure switch on the plane on June 9 of that year after a flight crew documented a problem two days before.
“However, the airline failed to perform a required inspection of the work before returning the aircraft to service,” the F.A.A. said in its statement on Tuesday.
United operated the aircraft on 23 domestic and international passenger flights before inspecting it on June 28 the F.A.A. said, referring to its remarks as allegations. “Two of those flights allegedly occurred after the F.A.A. had notified United that it had not performed the inspection,” the agency said.
The regulating agency proposed a civil penalty of $435,000 against United Airlines “for allegedly operating an aircraft that was not in an airworthy condition.”
“Maintaining the highest levels of safety depends on operators closely following all applicable rules and regulations,” Michael P. Huerta, the F.A.A. administrator, said. “Failing to do so can create unsafe conditions.”
Peter Goetz, a former managing director of the National Transportation Safety Board, said that he does not have the details of this particular case, but that the F.A.A. term “does not mean there is an imminent threat to safe flight. It can mean the air carrier did not follow its own repair and inspection procedures and was penalized.”
United has asked for a meeting to discuss the case, the agency said.
On Wednesday, Charles Hobart, a spokesman for United, declined to answer questions about the timing of any such meeting and about the airline’s response to the threat of a fine or the agency’s allegations. But he said safety was a “top priority.”
“We took action after identifying the issue and are working closely with the F.A.A. in their review,” Mr. Hobson said in an email. He declined to give details, such as whether the airline agreed with the assertion that the aircraft could have been unsafe.
United has weathered several controversies this year, including a furor that erupted on April 9 when cellphone video posted online showed a passenger being dragged off a domestic flight scheduled to depart from O’Hare International Airport in Chicago for Louisville, Ky.
The images sparked widespread outrage and became a public-relations nightmare for United. It later apologized and reached a settlement with the passenger, Dr. David Dao, and announced steps its employees would take to prevent such episodes from recurring, including a new process that would allow passengers to volunteer to give up seats for compensation, and increased the limit of that compensation to $10,000 from $1,350.
The airline also released a report suggesting that it needs to become more customer-friendly, and saying that it plans to reduce the number of flights it overbooks and to create a call center to handle overbooking problems.