Three U.S. airlines – including the two largest carriers at Cincinnati/Northern Kentucky International Airport – have agreed to each pay hundreds of thousands of dollars in fines to resolve government claims that they violated rules aimed at protecting consumers, CNBC reports. The U.S. Transportation Department said on Friday it fined Frontier Airlines $400,000 for violating oversales and disability rules; American Airlines (Nasdaq: AAL) $250,000 for failing to make timely refunds to passengers;…