Managing safety in the air traffic control terminal airspace

The air traffic control system is designed so that controllers are able to accept aircraft into their airspace and handoff aircraft exiting their airspace with minimal need to collaborate with other controllers. This system is designed to manage safety through constraints that rely on prohibitions and protections that limit scope of action. We contend that the focus on constraints has led us to neglect how controllers are actively and collaboratively managing safety. A framework of collaboration in ATC is proposed that guides the research. To provide a preliminary evaluation of this framework, ten observations were conducted with eight controllers handling normal traffic in a terminal control unit serving a city in Australia. Participants were all experienced controllers with a minimum of 25-year ATC experience and at least 10-year experience in their current position. In contrast to what would be expected if controllers were working within the constrained system as designed, 28% of the interactions between controllers could be classified as involving modifications to the plans for aircraft, which shows that controllers are actively managing safety. Further, different types of plan modification (replanning, plan amendment and building plans) and different strategies to negotiate plan modification (deferential, preferential and generational) could be identified. ATC procedures and training programmes are typically based on constrained safety and are largely silent on how controllers actively manage safety. We therefore need to include a consideration of how controllers are actively managing safety if we are to ensure effective system management now and into the future.