An Analysis of Merging and Spacing Operations with Continuous Descent Approaches

Abstract

Researchers at the NASA Langley ResearchCenter are developing the Airborne Precision Spacing (APS) concept to increase runway arrival throughput at capacity-constrained airports. Under APS operations, arrival capacity is increased by improving the precision of inter-arrival spacing at the runway threshold. Flight crews achieve this improved precision with the assistance of a new flight-deck system, which allows spacing operations to commence even while the aircraft and its lead are on different arrival routes to the runway. However, the increases in traffic volume that could be enabled by APS operations could also elevate noise concerns at busy airports.Noise-and fuel-efficiency concerns have independently motivated the air traffic management community to investigate Continuous Descent Approaches (CDAs) as alternatives to traditional arrival route profiles. However, uncertainties associated with CDA operations can cause runway capacity to be sacrificed. For this reason, CDA routes have only been implemented during lowdensity traffic operations.In this paper we report on current research into the integration of these two advancements, by employing APS operations to merge and space aircraft that are flying CDA arrival routes. Results obtained to date indicate that, while retaining the benefits of both techniques may be unachievable, APS operations can achieve narrow distributions of inter-aircraft spacing errors at the runway threshold for CDA routes. Analysis of the data also indicates that the spacing error distribution may be sensitive to inaccuracies in modeling the CDA trajectories for the aircraft and its lead.

Operational Concept for Flight Crews to Participate in Merging and Spacing of Aircraft

“…Initial results of this experiment show high correlation with past Langley experiments. 17,18,19 Figure 5 shows the behavior of the 26 th and 27 th aircraft in the middle of a 40 aircraft arrival stream merging in a nominal scenario. The momentary increase in airspeed at Top of Descent at the TRACON boundary (FL110) is due to the difference between ASTAR algorithm calculations and the aircraft's Flight Management System calculations.…”

Pilot response to off-nominal conditions in merging and spacing operation

“…Similarly, the confederate controller also recommended that pilots should space on an aircraft that is two or three aircraft ahead of 4.D. [3][4][5][6][7][8][9][10][11] them, instead of the one directly in front of them. The controller noted that controllers find this strategy an effective way to buffer the effects of transient spacing variations of the few immediately leading aircraft on a trailing aircraft.…”

“…Extensive simulation studies [6][7][8][9][10][11][12] have shown that interval managed CDAs is a viable concept that yields good spacing performance and throughput, considerable noise and fuel reduction, manageable pilot workload, and high pilot acceptance. A recent simulation has also been conducted to explore the effects of offnominal events introduced after the top of descent (TOD) [13].…”

A review of the impact of noise restrictions at airports

“…CDA (see Figure 1) allows aircraft to approach moderately dense terminal areas, eliminating the level altitude segments and their associated thrust transients at low altitude, while flying efficient, near-idle descent trajectories that save fuel, and reduce emissions and noise (Ren et al, 2011;Weitz et al, 2005). However, these procedures are not in use everywhere because effective implementation may be difficult since aircraft require special equipment and can have a negative impact on the airspace throughput and controller workload (Jackson, 2009;Reynolds et al, 2005).…”