Initial safety evaluation of the Unified Departure Operation Spacing (udos) standard concept

The initial spacing applied between departing aircraft is a major factor affecting the safety and 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 of the Same Runway Separation standard can often be applied. The Unified Departure Operation Spacing (UDOS) separation standard concept was developed as a separation standard alternative to increase the operational efficiencies where diverging departure operations are not feasible. This paper investigates how UDOS spacing applications would affect departure operations at airports across the National Airspace System (NAS). It presents the analysis approach taken to characterize departure performance parameters of aircraft observed in actual operations, the simulation model developed to quantify their impact on aircraft spacing, and the methodology used to validate model performance. The paper presents quantitative estimates of proximity event probabilities and outlines applicable controller mitigation strategies. The results demonstrate key advantages of employing Performance-Based Navigation (PBN) departure procedures that define a divergence waypoint. These advantages promise to largely eliminate controller workload limitations as a dependency for mitigation effectiveness.