Towards Fuel Efficient RNP Approaches

The latest edition of the ICAO Performance Based Navigation (PBN) manual (Doc. 9613 Edition 5), which was released late 2023, has requirements for a new Navigation Specification called “Advanced RNP (A-RNP)”. This Navigation Specification will require advanced aircraft navigation functions such as Radius-to-Fix (RF) leg capability and a Required Navigation Performance (RNP) of 0.3 Nautical Miles (NM) in all phases of an Instrument Approach Operation (except the Final approach phase and the Missed approach phase). Current procedure design criteria put a lot of constraints on Instrument Approach Procedures (IAPs), for example by limiting the Final approach segment length to a minimum of 3 NM and depending on the Navigation Specification and underlying approach technology, requiring an additional 2 NM Intermediate segment aligned with the Final approach segment for flight path stabilization. EUROCONTROL in cooperation with Lufthansa Aviation Training and the Swedish airport operator, Swedavia, has performed a study in which these existing design criteria have been relaxed, taking advantage of the increased navigation performance and advanced navigation functions of A-RNP, to investigate potential benefits and operational acceptance that enhanced IAPs could offer for the broader aviation community. The study investigated the potential to shorten Initial and Intermediate approach segments of an IAP and the transition from the Intermediate approach segment to the Final approach segment by using different aircraft types including aircraft equipped with state-of-the-art functions, such as a Localizer Performance with Vertical Guidance (LPV) function, Flight Management System (FMS) Landing System (FLS) and Integrated Approach Navigation (IAN). Tailored navigation databases including several RNP approach procedures using different coding options developed in cooperation with Lufthansa Systems, were provided by the FMS manufactures (Rockwell Collins, Honeywell, GE Aerospace). The procedures were tested in different scenarios with various winds and temperatures, using Level D certified full motion flight crew training simulators (B733, B748, A350, A320, A220, E190). The results proved the high potential of using A-RNP characteristics for the Initial and Intermediate approach segments to enable flight path shortening, by reducing the Final approach segment down to 3 NM and removing the additional aligned stabilization segment. Using modern navigation capabilities including RF legs to intercept the Final approach segment, available airspace in the Terminal Maneuvering Area (TMA) can be used more efficiently. Overall, these novel IAPs can reduce the distance flown with at least 4 NM, enabling efficient fuel- and noise-optimized routes for future operations. Additionally, they could facilitate the “Established on RNP” concept for parallel runway operations.