Air traffic control was a major federal computer system. It was one of the biggest and oldest. Repeated attempts to fix it had failed. The guys in the FAA used simple, old-fashioned computers dating to the 1970s. They used them because they were much more reliable than any of the modern ones. FAA guys had very dark jokes about computers crashing. For them, a computer crashing meant an aircraft crashing. It meant "a midair passenger exchange." It meant "aluminum rain."