Union officials expressed concern about security in US air traffic. "We can neither calculate the risk nor predict at what point the system will collapse," says an open letter reported by the Guardian and the New York Times. The text is signed by chiefs of air traffic controllers' unions, pilots and flight attendants.

For the past 34 days, parts of the government apparatus have been shut down in the USA. 800,000 federal employees receive no salary for weeks. Background is the dispute over the construction of a wall on the border with Mexico. US President Donald Trump calls for $ 5.7 billion, the Democrats reject that. Trump relies on their votes in Congress.

In their letter, the union representatives warn of the consequences of the shutdown: More and more employees would report sick, control posts at airports would have to close. There are as few air traffic controllers on duty as in 30 years not. The pilots worked in ten-hour shifts, six days a week.

Because of the budget dispute, the Federal Aviation Authority does not hire any new staff, the training had come to a standstill. Almost 20 percent of the pilots had reached retirement age. "If they decide to retire, the whole system is paralyzed."