Up to 20 percent of U.S. flights could be cut if the government shutdown drags on and air traffic controllers continue to go unpaid and refuse to work, Transportation Secretary Sean Duffy said Friday.The shutdown, already the longest in U.S. history, forced airlines to implement a 4 percent reduction in domestic flights at 40 of the country's busiest airports, effective Friday, following an order from the Federal Aviation Administration earlier this week.Citing increased stress and fatigue among air traffic controllers who have worked without pay, the directive, which came before millions o…READ FULL ARTICLE