4D Trajectory Based Operations — Speed Control Interoperability

Abstract

Arrival Procedures for Optimized Profile Descents (OPD) have been published to allow aircraft to approach many moderately dense terminal areas while flying efficient, near-idle descent trajectories that save fuel, and reduce emissions and noise. However, giving the aircraft flexibility in choosing their optimal vertical profile through altitude window constraints can have a negative impact on the airspace throughput and controller workload because spacing still needs to be maintained during the arrivals. Air Traffic Management automation systems and aircraft avionics using Trajectory Based Operations (TBO) concepts are being developed and fielded to assist controllers in handling traffic while allowing these efficient descent profiles. These systems are time-based, predict the aircraft trajectories as accurately as practical, and provide speed or time advisories to maintain spacing. Several specific methods are being developed: Flightdeck-based Interval Management (FIM), Ground-based Interval Management Spacing (GIM-S), and Time-of-Arrival Control (TOAC, also known as Required Time-of-Arrival, RTA). This paper describes the strengths and weaknesses of these systems, proposes how these three systems can be used together, when to use each of the methods, and expresses concern over an interoperability issue. The issue relates to the treatment of published speed constraints that differs between the current published standards and may prevent interoperability of the systems when approaching the terminal area. We propose to resolve the observed issue by updating the RTA / TOAC standards to allow treatment of the published speed constraints consistent with the FIM standards.