PERFORMANCE COMPARISON OF A320 AND 737NG REGARDING THE VERTICAL AND AND SPEED PROFILES IN ADVANCED RNP TO XLS ARRIVALS.

Kurzfassung

We report on the performance comparison between an Airbus A320 and a Boeing 737NG in vertical path following and speed profile during novel advanced required navigation performance (RNP) procedures which contain a fixed radius turn that delivers the aircraft onto a short ILS precision final. The approaches were flown automatically with guidance and automatic thrust as computed by the flight management system. Main areas of interest of the flight trials were the performance of the vertical path following during the RNP part of the procedure as well as maintaining an optimized speed profile during the continuous descent approaches. Within the PBN concept, it is possible to incorporate turns with a precise ground track into departure, en-route, arrival and approach procedures called fixed radius transitions or radius-to-fix. They offer the advantage of repeatable ground tracks during the turn and thus more freedom for the procedure designer when route planning in dense traffic, high terrain or obstacle rich environments. Additionally, ARINC 424 allows to specify altitude constraints at waypoints and vertical path angles for each RNP segment terminating at such a waypoint. The vertical path angle feature is currently largely unused and unexplored, except for the final approach segment of an RNP approach. These new options, when properly exercised, would allow any aircraft to benefit from better fuel efficiency during a continuous descent approach and a potentially reduced obstacle clearance due to the fixed vertical RNP profile and RF tracks. Ground tracks are repeatable and could be used for better noise abatement - besides their main purpose, obstruction clearance along the aircraft's path. In this study, we investigated the use of the ARINC424 coding options “vertical path angle” and “altitude constraints” at path terminators Track-to-Fix and Radius-to-Fix onto the performance of the speed profile for arrival time optimization and the vertical path following. Moreover, we study the influence of splitting the procedure into a standardt Terminal arrival route (STAR) and instrument approach procedure (IAP) components of varying lengths as shown in the Figure 1 below. The procedure designed for this experiment delivers the aircraft onto the instrument landing system of Braunschweig-Wolfsburg airport’s ILS runway 26. The glide path intercept point or final approach point (FAP) is located 1500ft above aerodrome level. The approach has 5 initial approach fixes (IAF) located 3,4,5,6 and 7 miles uptrack of the FAP. Additionally, 5 separate STARs were coded, all commence at the same point in the terminal area at an altitude of 4000ft MSL and ending at the respective IAF. The ground track for all 4 procedures is identical, only the transition from STAR to IAP is shifted. The descent angle from the beginning of the STAR until the FAP of the approach was designed and coded with 1° downwards. The idea is to test, where an automatic thrust reduction takes place in order to decelerate the aircraft as late as possible. We compare the performance between the two most commonly used passenger transport aircraft, the Airbus A320 and the Boeing 737NG. For the trials, we used DLR's own Advanced Technology Research Aircraft (ATRA), an Airbus A320 MSN659 with flight test instrumentation and a Thales flight management system (FMS) 2 as well as a Boeing 737-800 Simulator located at Lufthansa Flight Training in Berlin. The approaches were entirely flown using the auto flight guidance in managed mode and with automatic thrust activated. Results show that the 737 delivered the same performance at all 5 different coding options following the vertical and lateral path within the prescribed lateral and vertical required navigation performance. On the other hand, the A320 thrust reduction depended greatly on the point at which the IAF was located. The Airbus began to reduce thrust two miles before each the IAF which leaves insufficient time to decelerate in case of three miles track distance between IAF and FAP. While the B737 demonstrated the same behavior in vertical path following at all times, the A320s vertical path following depended on the energy state of the aircraft. In the “hot and high” case with 3 miles track between IAF and FAP, the vertical path was not maintained within the required corridor.