The funding halt means some 13,300 US air traffic controllers and thousands of other essential aviation safety officials must work without pay. The closure has led to staff furloughs throughout the government, even as vital functions such as aviation safety proceed. Some 13,300 US air traffic controllers and thousands of other essential safety officials must work without pay, according to a Department of Transportation (DOT) operational plan. The shutdown could delay key initiatives to recruit additional air traffic control staff and undertake a multi-billion modernization of the US air traffic control system, said the National Air Traffic Controllers Association. It listed activities that will "cease" during the funding gap including aviation rulemaking, air traffic performance analysis, investment planning, and financial analysis and audit.