At 6 a.m. Friday, airlines in the U.S. began cancelling flights in accordance with the FAA’s official order to reduce service at America’s busiest airports. The agency said the cutbacks are necessary to relieve pressure on air traffic controllers who've been working without pay for more than a month due to the government shutdown. Many have begun calling out of work as financial strain and exhaustion have reached a tipping point after enduring six-day work weeks with mandatory overtime.