Concept and benefits of a unified departure operation spacing standard

The initial spacing applied between departing aircraft is a major factor affecting the efficiency of departure operations at an airport. When departure operations are conducted under Instrument Flight Rules (IFR), successive in-trail departures must be provided a minimum of 3 nautical miles (NM) radar separation unless visual separation is applied. However, if the departure paths diverge by 15 degrees or more immediately after takeoff, reduced initial spacing can often be applied: separation is provided by the increasing lateral distance between the aircraft rather than by a fixed in-trail distance. The smaller initial spacing when diverging departures can be conducted leads to more departures per hour. This paper explores options for application of efficiency-enhancing reduced departure spacing and presents the concept of a single separation rule, the Unified Departure Operation Spacing (UDOS) concept, where the same reduced initial spacing is generally applied whether or not the departure paths diverge. The paper reviews the currently applicable standards, describes the analysis and simulation approaches taken to assess longitudinal spacing observed in actual operations, and provides estimates of potential operational benefits.