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.