Curved Approach Segments for Noise Abatement

M. Troller, R. Germann, A. Frik, M. Bertschi, P. Truffer, M. Scaramuzza

Abstract:	Noise protection has an increased importance for approach und departure procedures in vicinity of airports. Flight tracks should be focused over sparsely populated areas to the greatest extent possible. ICAO's new amendment of the Performance-Based Navigation manual will allow Radius-to-Fix (RF) legs during initial and intermediate segments of an approach. Standards for procedure design are currently in development. However, before starting the final approach, a straight segment for aircraft stabilization is required in case of xLS approaches. Switzerland has many congested and extensively fragmented airspace due to various user requirements. Airspace changes are extremely complex and time-consuming. Consequently, the use of airspace should be optimized as far as possible, also in respect of noise-sensitive areas. Applications with RF legs are a major enabler for such advanced procedures. To minimize airspace use and to optimize fuel consumption, it is even desired to have various RF legs in one approach procedure with the last one ending directly at the beginning of the final approach segment. In the frame of the Swiss-wide implementation program to promote GNSS procedures and applications, test flights were carried out to analyze the use of various RF leg applications in an approach procedure. Two different approach scenarios were developed. The first scenario was designed according current ICAO standards with one RF leg and a straight stabilization segment of 2 NM before the final approach segment. The second scenario includes three RF legs, the first one to the right, followed immediately by a second and third leg, both, to the left. Latter ends directly at the start of the final approach segment. This scenario is not yet covered by current ICAO criteria. A maximum bank angle and wind conditions without safety margins dedicated to the deployed aircraft were applied to go to the limits of what is technically possible. Both scenarios were designed with an ILS and RNAV final approach segment. Test flights have been carried out with a Super King Air of the Swiss Air Force. This aircraft is equipped with the Pro Line 21 system having RF leg capability, a Rockwell Collins GPS4000S GPS/SBAS receiver and a RTCA DO260A-compliant ADS-B out transponder. A total of 13 approaches have been performed. The aircraft has been equipped with a geodetic GNSS receiver in order to record raw GPS measurements on both, the L1 and L2 band. These measurements have been post-processed using data of the permanent automated GNSS network for Switzerland to determine the true flight path with an accuracy of better than 10 centimeters. The navigation system flight path has been determined by recording ADS-B messages. Finally, the navigation system error and the flight technical error have been calculated and analyzed. The test flight results have been analyzed concerning compliance to the ICAO RNP1 specification. The flights have been performed with different settings of the autopilot and the flight director. Furthermore, configurations with deselected or switched off GPS and deselected DME have been tested. The performance boundaries of RNP 1 could be maintained for all flights. Even abnormal conditions with AHRS (Attitude Heading Reference System) only resulted in an acceptable performance. The scenario with an ICAO-compliant RF leg followed by a stabilization segment before the final approach segment did never show any significant deviation from the designed flight track. The scenario with three RF legs currently not covered by the ICAO design criteria did show surprising results. The transition from the last RF leg to the final approach segment without a straight intermediate segment did not show any significant deviation from the designed flight path. This holds true for the interception to an RNAV as well as to an ILS final approach segment. The so-called "S-design" of RF legs, i.e. an RF leg immediately followed by an opposite RF leg is in line with the current ICAO design criteria. However, the test flights showed significant lateral deviations of up to 0.3 NM for this scenario if the approach is performed with the autopilot. This paper describes the test flights carried out and the analyses performed to obtain important findings for the enhancement of flight design criteria in respect of flexibility of approach procedures and avoidance of flights over noise-sensitive areas.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	333 - 339
Cite this article:	Troller, M., Germann, R., Frik, A., Bertschi, M., Truffer, P., Scaramuzza, M., "Curved Approach Segments for Noise Abatement," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 333-339.
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