Domestic flights at 40 of the country's busiest airports will be affected as officials try to ease pressure on air traffic controllers. The Federal Aviation Administration (FAA) says reductions will start at 4% of internal flights before rising to the full 10% by the end of next week - it warns up to 4,000 flights per day could be affected. Control towers at airports have been grappling with absences of air traffic controllers, who are either calling in sick or taking side jobs as they work without pay during the federal government shutdown. Several of the largest US airlines are assuring customers they'll be able to get full refunds for the cancelled flights - here's what some, including United and Delta, are saying. (BBC)