Air traffic control language is commendably succinct. The advisory message that was sent out by the US Command Center at 11.50am GMT on Christmas Eve read: “Nationwide ground stop for all AAL Main and Subs”.
AAL is American Airlines, and the instruction to air traffic controllers across the US (and, as it emerged, the world) was to prevent the carrier’s planes from taking off. The fact that it affected “Subs” – smaller airlines flying regional trips for American, as well as the mainline operation – suggested something had gone awry with the departure control system. This is the technology that manages crucial elements of dispatching a flight, from check-in to load control – ensuring that the weight of passengers, cargo and fuel is appropriately distributed on the plane.
