Robert Geister

Curved approach procedures enabled by a Ground Based Augmentation System

As the international air traffic increases and becomes more and more complex there is a growing demand for new operational procedures where noise and terrain issues are being considered increasingly. The proceeding integration of satellite navigation into aviation is paving the way for more flexible and complex approach procedures. Operationally, the Required Navigation Performance (RNP) determines the specifications an aircraft has to fulfill to perform a specific procedure. The use of a Ground Based Augmentation System (GBAS) could provide the required accuracy and integrity while loosening the requirements on the aircraft equipment. GBAS is certified as a system providing CAT I capabilities for a precision approach in an ILS “Look-Alike” fashion but in addition the architecture of a GBAS already contains the possibility to provide data for complex procedures, called Terminal Area Paths (TAP). Within this work, the data architecture of TAP messages was incorporated into a cockpit simulator and trials regarding flyability were conducted. For every waypoint in a TAP, a specific horizontal and vertical sensitivity value can be assigned. Therefore, different values for this sensitivity value were investigated during simulated approaches that were flown manually and automatically. Different means of displaying the deviation information were provided to the pilots. The results in terms of Flight Technical Error (FTE) for different approach paths flown automatically and manually are presented. An analysis of the different waypoint sensitivities and means of displaying deviation information is going to be carried out. Based on the observed FTE values, a first link between GBAS TAP performance and existing RNP values for the approach phase of a flight is going to be established.

Towards higher levels of automation in taxi guidance: Using GBAS Terminal Area Path (TAP) messages for transmitting taxi routes

According to Sheridan and Verplanks classification of levels of automation, taxiing on an airport still has a very low automation level. Key element for increased automation in taxi guidance is a precise and reliable navigation capability. As a Ground Based Augmentation System (GBAS) can fulfill the stringent requirements for a precision approach, it can play an important role in providing the required navigation performance during taxiing as well. This paper will explain the use of GBAS for taxi guidance. It presents, how the required navigation performance for automatic taxiing can be provided using GBAS. Besides the highly precision position service provided via Differential GPS, the Terminal Area Path (TAP) messages will be used to provide the aircraft with accurate and reliable information about the taxi route. Taxi trials with DLRs A320 research aircraft ATRA (Advanced Technology Research Aircraft) and the GBAS ground station at airport Braunschweig-Wolfsburg (EDVE) showed that over the whole maneuvering area the received VHF signal level was adequate for transmitting such a “Ground-TAP”. These tests were performed with an antenna on the aircraft located at a height of 8ft, which is lower than the actual required coverage minimum of 12ft defined in ICAO Annex 10. Together with a redefined voice communication structure and a list of predefined routes the use of GBAS for taxi routing functionalities of an Advanced Surface Movement Guidance & Control System (A-SMGCS) is feasible. Due to the independency from an on-board database the combination of such a message broadcast and the GNSS based positioning can be the key enabler for a future auto taxiing functionality.

Flight testing of noise abating required navigation performance procedures and steep approaches

To test different types of noise abatement approach procedures the Institute of Flight Guidance and the Institute of Aerodynamics and Flow Technology performed flight tests on 6 September 2010 with a Boeing 737-700. In total, 13 approaches to the research airport in Brunswick, Germany (EDVE) were flown while the approach area of the airport was equipped with six noise measurement microphones. Brunswick airport is equipped with an experimental ground based augmentation system which allows the implementation of 49 instrument landing system (ILS) look-alike precision approach procedures with different approach angles simultaneously.

Integrating RPAS - published approach procedures vs. local arrangements

This paper presents the setup, the assessment methods, and the results of a flight trial that was conducted in June 2016 in order to demonstrate integration of remotely piloted aircraft systems (RPAS) into the current airspace, while also acknowledging that there are challenges to overcome. An RPAS demonstrator received a flight plan from the ground control station (GCS) using a ground-based data link, departing from Braunschweig-Wolfsburg airport and flying towards Leipzig/Halle airport on published routing. When approaching Leipzig/Halle airport, the data link was lost as predicted, and the arrival procedure was altered by air traffic control (ATC), which showed that an additional and dedicated RPAS controller at arrival airports might be valuable and advantageous. Focus of this paper is the description of the components that were used during the trial and their interconnectivity, the evaluation of quantitative recorded data and the qualitative experienced difficulties and challenges. Assessment of the recorded data is divided into data link quality, data link latency, and flight following performance (vertical and lateral following accuracy), with the latter being linked to existing performance based navigation (PBN) parameters by ICAO and height-keeping performance values by EASA. The paper concludes with a discussion on the investigated integration concept.

Automatic speed profiling and automatic landings during advanced RNP to xLS flight tests

We report on the performance of our Airbus 320 during novel advanced required navigation performance (RNP) procedures which contain a fixed radius turn that delivers the aircraft onto a short ILS precision final above aerodrome level. The approaches were flown automatically with guidance and autothrust as computed by the flight management system. Main areas of interest of the flight trials were the performance of the autoland capability, 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 exists the possibility 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. Whilst offering these benefits such advanced RNP approach operations are still non-precision procedures and automatic landings cannot be performed after their successful completion. Hence, to enable automatic landings and to extract maximum benefits from RNP operations, they must transition into a precision final approach segment provided by any precision landing system (ILS, GLS, MLS) so that the guidance loops for flare and land modes of the auto flight guidance system can activate. This is often called RNP to xLS (or RNP2xLS). Moreover, 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 aircrafts path. In this study we investigated the use of the described ARINC424 coding options onto (a) the performance of the speed profile for arrival time optimization (b) the vertical path during the RNP part of the procedure and (c) the performance of the autoland capability after a curved transition onto an ILS. For the trials, we designed five instrument approaches to runway 26 at Braunschweig-Wolfsburg airport, which is equipped with an Instrument Landing System. A RF curve terminates at the ILS intercept point at heights 550ft, 750ft, 1000ft, 1500ft and 2000ft above aerodrome level and each approach had four different initial approach fixes which corresponded to a track angle change of 30,60,90 and 180 degrees during the constant radius turn-to-final. For each initial approach path coded as advanced RNP segments, we programmed different combinations of vertical path angle and height constraints at waypoints. Moreover, as the thrust computer automatically reduces speed to a value suitable for initial approach, we varied the distance of the initial approach fix of one of the approaches from ranging between 3 to 7NM from the FAF in order to allow the aircraft to decelerate as late as possible. For the trials, we used DLRs own Advanced Technology Research Aircraft (ATRA), an Airbus A320 MSN659 with flight test instrumentation and a Thales FMS2. The approaches were entirely flown using the auto flight guidance in managed mode and with auto-thrust activated. The approach mode was armed either at the FAF or before the initial approach fix. We show supporting evidence that RNP2ILS approaches can be safely flown all the way to an automatic landing using the flight management guidance computer and the auto flight control system. In order to fly the desired path with vertical path angle during the RNP initial and intermediate approach, a separate mode (such as LNAV/VNAV) different from the singular approach mode would need to be implemented in the aircraft. Additionally, airlines and other operators currently apply stabilization criteria following which the aircraft must be established on a straight final with the correct sink rate at 1000ft above aerodrome level in order to continue the approach. For landings in low visibility conditions, more stringent criteria are often applied. An operational implementation of RNP2ILS approaches with a curved final intercept would require a rephrasing of the criteria to include a concept such as RNP established.