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A new converter technology allows suitably equipped aircraft to use data provided by the satellite-based augmentation system in receivers originally designed for the ground-based augmentation landing system. For these aircraft, that system enables a lower decision altitude and, hence, improved access to airports. To make this technology usable, air crews require an operational concept and the flight crew has to be presented with the appropriate information in the form of approach charts. Two different possibilities for an operational concept were developed and the corresponding approach charts created. One option is a modified area navigation approach chart, to which the specific information is added. The other chart is an entirely separate procedure for the approach. These two options were tested with airline pilots in an Airbus A320 full-flight training simulator. During the simulator flights, aircraft performance data was recorded and the participants filled in questionnaires regarding workload and quality of the operational concept. The results show different behavior during the intercept of the final course, but all approaches remained within the required limits. The questionnaires revealed that the workload is higher during the area navigation variant and that all participants prefer the separate ground-based augmentation landing system variant.

Required navigation performance procedures are a cost-effective and accurate solution for aircraft instrument approaches, especially when combined with a final approach segment utilizing satellite based augmentation. However, transport category aircraft are currently not equipped with the satellite based augmentation for precision guidance. An existing converter technology can provide this final approach segment to aircraft equipped with the GPS landing system. Then, as an added bonus, an automatic landing at pilots discretion is possible after the presented approach. Here, we study Thessaloniki and Corfu airports, both accommodating a large number of transport category aircraft, with many ground infrastructure constraints. Both were recently equipped by the Hellenic air navigation service provider with RNP approaches. We successfully flight tested the satellite based augmentation to GPS landing system converter and show that both airports could benefit from a permanent installation of such a system by having fewer diversions.

Abstract. Head-up displays (HUD) assist pilots, especially in the approach and landing phase. In this paper we compared pilots’ eye-tracking behavior between a pathway-in-the-sky layout versus the more conventional two-dimensional symbology in an HUD in a fixed-based cockpit simulator. In particular, we wanted to assess how visual attention was distributed within each layout (tunnel and standard). Performance and eye-tracking data were recorded, as well as workload and situation awareness measures. Results showed that the tunnel-in-the-sky symbology provided a very high tracking performance with low perceived workload and high perceived situational awareness. The analysis of the eye-tracking data revealed possible attentional tunneling with the tunnel-in-the-sky symbology and large differences between the displays in the distribution of visual attention.

Introduction The increase of Radio Frequency Interference (RFI) events is a well-documented trend, that is becoming a threat to the use of Global Navigation Satellite Systems (GNSS) in aviation. EUROCONTROL’s voluntary ATM incident reporting system EVAIR is a platform for pilot to report relevant incidents, such as GNSS outages. In the years 2018 and 2019 more than 4300 and 3500 GPS outages were reported compared to less than 500 events in the previous years. While the tool is giving a good geographic perspective about the typical RFI hotspots, it is ultimately based on voluntarily reported data. As pilots get used to widespread RFI in certain areas and Notices to Airmen (NOTAMs) are published that RFI should be expected, these events are considered to be normal. This likely leads to the numbers behind the GNSS outages reported in EVAIR being significantly underestimated. In this presentation we will give the audience a feel for why we believe this to be true: outages in GNSS service due to RFI initially manifest themselves in the cockpit in subtle ways, not immediately identifiable to the unaware. Background The Nicosia Flight Information Region (FIR) has long reported difficulties with GNSS service coverage. It regularly issues NOTAMs warning pilots of the phenomenon and kindly requests radio reports of such observations. Pilots regularly report loss of GNSS on approach to Larnaca International Airport (LCA) making the introduction of GNSS-based approach procedures impossible. While many aircraft can cope with GNSS outages easily by using terrestrial navigation aids and/or Inertial Reference Systems onboard the aircraft, some aircraft do not have this option and may require ATC support. This is causing an increase in workload for air traffic controllers and pilots of the affected aircraft alike. As a way to better understand the prevalence of the phenomenon and its implications on main-line aircraft, DLR flew its Airbus 320 to LCA, equipped with a variety of GNSS monitoring instruments, including the baseline avionics of the aircraft, a set of experimental GNSS receivers and a recorder for sampling the raw radio signal. Observations and Data An important feature of the flight is that we have been able to analyze the phenomenon from several perspectives. This includes photographs of the cockpit displays, and matching recordings of GNSS signals, where available, in terms of pseudorange and signal-to-noise ratio. In addition, we collected raw, pre-correlator signal samples, the analysis of which offers a very particular type of insight. The raw signal was captured with a recording device, after being downconverted to baseband. The sampling rate was set to 30.7 MHz, at eight bits per sample. This quality of recording allows us to study the response of a GNSS receiver in “playback” mode, but it also enables an analysis of the frequency contents of the radio band in question. Reception and Impact While it is not a particularly novel message that GNSS signals are being jammed with RFI in some parts of the world, the aviation community has already reacted to our findings. Some of the results have been discussed at EUROCONTROL-hosted events, as well as a white paper. The Cypriot Department of Civil Aviation has, since, stated that the measurements prompted a revision of the threat model behind the RFI events. As for the wider aviation community, these observations and measurements clearly show a need to revise the paradigms for the provision of resilient navigation services. An outdate understanding of the RFI threat was based on individual drivers sporadically disrupting GNSS services at airports, for example by using GNSS privacy devices. Our measurements make it evident that this threat model is outdated, as GNSS outages clearly last several hours (potentially even more) and cover an entire FIR. The Presentation We will present the measurements and results discussed above in a presentation designed to create awareness of the impact of RFI on avionics hardware. During this flight we observed that it is easy for pilots to underappreciate the degree of disruption to their GNSS avionics. An important part of the message is that we have found no evidence of intentional misleading, inside the GNSS signals. The service disruptions are likely collateral to the geopolitical reality of the region. In this sense, the results show that there is no direct threat to the safety of air traffic and, consequently, the need to act may not be acute. The results do, however, show a need to modernize the airspace and CNS infrastructure, to reflect the evolving nature of the RFI threat. We consider it important to point to the reduction in redundancy, and therefore in safety, that stems from a systematic, permanent disruption of the primary means of navigation. Disruptions of GNSS are also known to increase controller workload and cause other forms of operational expenses, for example due to increased numbers of go-arounds.

We designed and built a system intended to combine the advantages of both the ground based and the satellite-based augmentation systems (GBAS, SBAS) by using a converter between them. In both GBAS and SBAS, instant integrity information is provided by estimating protection levels, a high probability bound for the computed position. This is then compared to the alert limit of the respective system. Since both systems are quite similar, and the SBAS signal can nowadays be decoded even by low cost receivers, one can receive the augmentation data from the SBAS, slightly modify it to fit into the GBAS data structure and broadcast this data to a GBAS equipped aircraft. Said aircraft could execute an RNP approach with the Localizer Performance and Vertical guidance (LPV) final approach segment which would otherwise not be available. This may come especially handy in places where no non-precision minima are published, such as the RNP-E approach into Innsbruck and Salzburg, or where no other approach procedures are available to spatial or monetary constraints. Since there are slight differences between the two systems, we made sure that integrity for the safety-of-life approach service is ensured. We named the system GLASS (GLS Approaches using SbaS), built a prototype and began trials with real GBAS avionics hardware.To accomplish this, we created a hardware in the loop environment, which allows us to validate various receivers without having to go through a full flight certification of the hardware. We tested this environment using the DLR in house full motion rotorcraft simulator to fly point in space approaches during Helicopter Emergency Service (HEMS) missions.The test bench setup consists of an Orolia GSG5 GPS and SBAS simulator connected to both an SBAS receiver and a Funke Avionics GPU400 GLS receiver. The SBAS receiver is subsequently connected to a GLASS Station PC, which translates the SBAS corrections to GLS conformal structures and broadcasts them using a Telerad 9009 VDB GLS transmitter. This transmitter is also connected to the VHF data broadcast input of the GPU4000. The Orolia GSG5 receives data updates from the DLR flight simulator Aves (Figure 1).During the trials, the accuracy and integrity of both receivers behaved as expected. However, the Collins GLU925 showed an anomaly: if two corrections were broadcast with the same IODE parameter, the second one was ignored. This limits the availability of the system unnecessarily. Moreover, we found that both digital avionics devices did not evaluate the approach performance designator, one parameter of the final approach segment date block. This actually increases integrity while also limiting availability at the same time.

When using GNSS navigation for final approach guidance of aircraft to a landing site, the only systems currently available are differential GNSS with additional integrity data called augmentation systems. These work well when the landing site is fixed in space and well surveyed. In all other cases, augmentation systems are difficult to use. Here, we propose relative navigation based on GNSS double difference measurement to accomplish the same task, but also onto moving landing platforms or at unsurveyed locations. We call this the Beacon Landing System. Furthermore, we show long term measurement data confirming the sub-meter accuracy and results from flight tests. During the flight test we successfully used the relative navigation for aircraft guidance.

We designed and built a system intended to combine the advantages of both the ground based and the satellite based augmentation systems (GBAS, SBAS) by using a converter between them. We installed a prototype system at Salzburg Airport and flight tested it on 12th of February 2020 using DLR's A320 test aircraft equipped with flight test instrumentation. Using our system, 3D GLS type approaches are possible at any airport within the coverage of the SBAS. The system includes an SBAS-capable global navigation satellite systems receiver with a database and a GBAS-compatible data link. The correction and integrity data received from the SBAS satellite are automatically translated into GBAS compatible structures and sent to the airborne GBAS receiver using the final approach segment data block Without SBAS the system can revert to differential GPS. In both GBAS and SBAS, instant integrity information is provided by estimating protection levels, a high probability bound for the computed position. This is then compared to the alert limit of the respective system. Since both systems are quite similar, and the SBAS signal can nowadays be decoded even by low cost receivers, one can receive the augmentation data from the SBAS, slightly modify it to fit into the GBAS data structure and broadcast this data to a GBAS equipped aircraft. Said aircraft could execute a RNP approach with the Localizer Performance and Vertical guidance (LPV) final approach segment which would otherwise not be available. This may come especially handy in places where no non-precision minima are published, such as the RNP-E approach into Innsbruck and Salzburg. Since there are slight differences between the two systems, we made sure that integrity for the safety-of-life approach service is ensured. We named the system GLASS (GLS Approaches using SbaS), built a prototype and tested it with real GBAS avionics hardware. We performed 4 approaches to Salzburg Airport in Austria (LOWS). Salzburg is now equipped with a RNP approach using LPV only to runway 15 with significantly a lower minimum than the RNP approach with LNAV minimum called the RNP E 15. This is due to the location of the new missed approach point. Using the GLASS system, all GLS equipped aircraft would be able to take advantage of this new minimum line. We followed the approach track using FMS guidance and recorded the ARINC 429 output from the Collins GLU925 Multimode Receiver (MMR). The GLASS guidance was provided to the pilot on the electronic flight bag display for reference. We show a complete analysis of integrity data, MMR status information and MMR output guidance. We compare the GLS data from the MMR with standard SBAS data from an onboard Septentrio PolaRx3 receiver. The GLASS system provides the LPV final approach segment to GLS-only equipped aircraft such as the Boeing 737-800. This can enable increased access to airports that are currently not equipped with an xLS type approach such as Innsbruck (LOWI). Especially approaches in France could be of interest, since the government has officially declared to decommission all category I ILS installations in favor of RNP approaches with LPV. The system could also be carried on the airborne side rather than be a fixed installation on the ground. With a pilot selectable FAS block, it could enable LPV approaches without modifications to existing airborne hardware. Thus, any GLS capable aircraft could fly LPV approaches without requiring ground infrastructure modifications. In this case, the protection level scaling from GBAS is not an issue, since it can be compensated for by the GLASS system.

We report on the flight test results of an Airbus 320 during novel advanced required navigation performance (RNP) procedures which contain a fixed radius turn that delivers the aircraft onto a short instrument landing system (ILS) precision final. Moreover, the advanced RNP part contains altitude constraints and/or a coded vertical path angle. The approaches were flown automatically with guidance and autothrust as computed by the flight management system. We investigated the use of the fixed radius in conjunction with vertical path options onto (a) the performance of the speed profile for arrival time optimisation, (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 a runway equipped with ILS. A RF curve terminates at the ILS intercept point at heights of 550, 750, 1000, 1500 and 2000 ft 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° during the constant radius turn-to-final. We constructed the procedure such that the altitude constraints at initial, intermediate and final approach fix describe a continuous vertical path with minus 2° inclination, transitioning to the –3° glide path of the ILS and intercepting the glide path from below. In all cases, the land mode of the flight guidance computer became active between 316 and 381ft radar altitude. The vertical path following error depended on the coding of the procedure in the database. With coded vertical path angle and altitude constraints, the vertical path following error was never greater than +57 m (above desired flight path) during the RNP part when flown by the automatic flight guidance system without any pilot intervention.

In security-critical situations in the maritime area, ship-based deployment of remotely piloted aircraft systems could enable automated acquisition of aerial images and other sensor data. If intervention is required, response times of federal institutions could be shortened significantly without endangering personnel. This paper gives an overview of research undertaken at DLR in cooperation with the German Federal Police for Maritime Tasks. For a safe ship deck landing of an unmanned rotorcraft a combination of precise navigation and tethered landing system has been developed and patented. Relative double-difference algorithms are used for precise navigation of the rotorcraft to a hover point over the ship deck. From there, an electromagnetic winch is lowered from the rotorcraft that connects to the ship deck. The resulting cable connection is used for aligning the rotorcraft during landing and securing it on the ship deck afterwards. First demonstrations on a real ship deck show the feasibility of the system.

We built a prototype system intended to combine the advantages of both the ground based and the satellite based augmentation systems (GBAS, SBAS). The system includes an SBAS-capable global navigation satellite systems receiver with a database and a GBAS-compatible data link. The correction and integrity data received from the SBAS satellite are automatically translated into GBAS-compatible structures and sent to the airborne GBAS receiver using the final approach segment data block. In both GBAS and SBAS, instant integrity information is provided by estimating protection levels, a high probability bound for the computed position. This is then compared to the alert limit of the respective system. Since both systems are quite similar, and the SBAS signal can nowadays be decoded by even low cost receivers, one can receive the augmentation data from the SBAS, slightly modify it to fit into the GBAS data structure and broadcast this data to a GBAS equipped aircraft. Said aircraft could execute a RNP approach with the Localizer Performance and Vertical guidance (LPV) final approach segment which would otherwise not be available. This may come especially handy in places where no non-precision minima are published, such as the RNP-E approach into Innsbruck. Since there are slight differences between the two systems, we made sure that integrity for the safety-of-life approach service is ensured. We named the system GLASS (GLS Approaches using SbaS), built a prototype and tested it with real GBAS avionics hardware. We implemented the system in C++ on a 64 bit Linux PC and connected this PC to a Telerad VDB Transmitter. The necessary correction data was obtained from a Septentrio AsteRx3 GNSS receiver. We used the standard final approach segment (FAS) data blocks as published for Braunschweig-Wolfsburg Airport (ICAO Identifier EDVE) in the German AIP for runway 08 and runway 26. We ran ground bench tests, using customized software to calculate SBAS and GBAS Positions and Protections Levels using standard algorithms published in DO253D and DO229D. Data collected during one week starting on 24 October 2018 shows availability for the standard EGNOS approach service of 99.96% and a reduction to 92.4% availability using the converter system with the inflated protection levels. If it were possible to increase the VAL to the SBAS standard of 50m, the availability of the system would increase to 99.95The standards for data transmission in a GBAS system only allow a maximum value of 25.4m to be entered as a Final Approach Segment Vertical Alert Limit (FASVAL) as opposed to the SBAS LPV approach service FASVAL of 50 m. However, GBAS final approach segment alert limits are scaled with distance from the glide path intercept point (GPIP), which is typically about 1000ft upwind of the landing threshold. This may lead to an availability and continuity issue which has to be further evaluated. One possible solution is to find an acceptable height/distance combination, below which alert levels are more stringent than LPV and above which they are more relaxed. Setting the FASVAL to its maximum, this would occur at approximately 320m above aerodrome level without the penalty in availability being greater than discussed above. The GLASS system provides the LPV final approach segment to GLS-only equipped aircraft such as the 737–800. This can enable increased access to airports that are currently not equipped with an xLS type approach such as Innsbruck (LOWI). Especially approaches in France could be of interest, since the government has officially declared to decommission all category I ILS installations in favor of RNP approaches with LPV. Moreover, the system could be carried on the airborne side rather than be a fixed installation on the ground. With a pilot selectable FAS block, it could enable LPV approaches without modifications to existing airborne hardware. Thus, any GLS capable aircraft could fly LPV approaches without requiring ground infrastructure modifications. In this case, the protection level scaling from GBAS is not an issue, since it can be compensated for by the GLASS system.

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.

Due to time constraints this paper unfortunately only contains a fraction of the analysis and data collected during flight trials. For a detailed comparison see the future journal publication of this research. We report on using Global Navigation Satellite System (GNSS) pseudorange based double differences for relative navigation in the form of a beacon landing system and present an associated display and results of flight test data. In surveying, real time kinematics is an established technique that uses GNSS carrier phase measurements for highly precise position estimation. Part of the RTK process is to form the double difference observable between master and rover receiver and between pairs of satellites. With this double difference and knowledge of the satellite geometry, it is possible to calculate a relative position between two GNSS receivers. When using carrier phase measurements, the rover needs to be stationary for some time in order to initialize the resolution of the carrier phase ambiguities. The same technique can be used on pseudorange measurements without the limit of stationarity for initialization, albeit at the cost of a decreased accuracy. Almost all correlated errors are removed from the solution in the process of differencing [1] and the resulting DD observable has an accuracy that is comparable to the ground based augmentation system. For the double difference code measurements it is possible to calculate protection levels and thus thus guaranteeing the integrity of the solution [2]. Ground Tests show that the scalarized accuracy of the baseline vector is below 1m RMS We apply the double difference code technique to a system of aircraft receiver, ground maker receiver and Freewave serial data link in order to calculate the relative vector between the two GNSS Antennas. When the ground marker receiver is located on suitable landing site, this system can be used as a Beacon Landing System (BLS) where the aircraft receiver calculates deviations to a desired approach direction and approach angle. Shown on a suitable display, the pilot can follow the selected lateral and vertical track to the desired location for a successful landing or other mission. We tested this system using a setup of two Novatel OEM Star receivers running at 2Hz, one on the ground and the second one onboard the aircraft. The ground receiver is placed near the runway of our test airport in Athens, Ohio. Moreover, we provide the pilot with a display showing a horizontal situation indicator (HSI) with user-selectable approach direction and vertical angle on a small tablet computer mounted on a control yoke. The pilot selected a three degree approach angle and the runway direction of the approach end where the receiver was placed. We performed three approaches and analyzed the data using post processed dual frequency carrier phase solution with fixed integer ambiguities as a reference. The system worked well, similar to GBAS CAT1 performance without the need for precisely surveyed receiver locations but lacking the reference receiver failure redundancy. It could be used for applications, where only a relative position is relevant, such as landings of unmanned surveillance aircraft on moving platforms. Alternatively it can be applied in in situations when it is not possible to perform extensive surveying of the landing site, for example at a military forward operating bases.

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 aircraft's 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 DLR's 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.

Ionospheric disturbances present a considerable hazard to single-frequency satellite navigation systems for airborne users. We discuss our implementation of three ionospheric threat models in the DLR "multi-output advanced signal test environment for receivers" global navigation satellite system simulator, which is based on Spirent GSS 7780/7790 signal generator. These threat models include the standard front-based threat model developed for the integrity assessment of ground-based augmentation systems (GBAS), a simplified plasma bubble model, and ionospheric scintillation, which can be combined with either of the two previously mentioned models. These effects can now straightforwardly be simulated at the German Aerospace Center's research facilities. As an example, we simulate a GBAS ground facility with code–carrier divergence monitoring, affected by an ionospheric front, and we show the results of a simulation with coincidental occurrence of a plasma bubble and scintillation with an S 4 index of 0.4.

Four basic error sources exist for residual pseudo-range errors in a single frequency differential GPS system for ground based augmentation (GBAS): signal multipath, increased receiver noise (carrier-to-noise density ratios (C/N0)) due to interference, residual differential troposphere error, and the error induced by ionosphere gradients. Without restricting ourselves to classical Gaussian overbounding, we combine their probability density functions (pdfs) to a total pseudo-range error distribution. This distribution is propagated through the GBAS Hatch filter and then mapped into the position domain using a worst case (selected by maximum vertical dilution of precision (VDOP)) of a full 31 satellite constellation with the two most critical satellites failed observed at Braunschweig Airport, Germany. Our calculations yield a significant reduction amounting to 46% of the position domain error at the 1.5 × 10-7 integrity risk level when compared with the classical Gaussian overbounding approach.

International audience; Resonant coupling between the Earth and the atmosphere at frequencies where the solid Earthmodes overlap the fundamental modes of the atmosphere allows for the triggering of oscillatoryacoustic perturbations by ground excitation and vice versa. Here, we describe oscillatoryperturbations observed in the solid Earth (from volumetric borehole strainmeter data) and inthe atmosphere (from GPS-derived ionospheric total electron content) following the 2003 July13, Soufri`ere Hills Volcano explosion (Montserrat, Lesser Antilles). Spectral analysis showsan amplitude peak at 4 mHz for both data sets, with similar waveforms and signal duration.Using a normal mode summation technique, we show that both signals are explained by asingle explosive source in the atmosphere. Similarities in waveforms, in particular a doublewave train also reported after several other explosion-triggered atmospheric perturbations,result from the superposition of the dominant (fundamental) atmospheric modes that triggerresonant coupling with the solid Earth around 4 mHz.

We performed an extensive experimental campaign (the spread F Experiment, or SpreadFEx) from September to November 2005 to attempt to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12 and the GUVI instrument aboard the TIMED satellite. Initial results of our analyses of SpreadFEx and related data indicate 1) extensive gravity wave (GW) activity apparently linked to deep convection predominantly to the west of our measurement sites, 2) the presence of small-scale GWactivity confined to lower altitudes, 3) larger-scaleGWactivity apparently penetrating to much higher altitudes suggested by electron density and TEC fluctuations in the E and F regions, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent direct links of these perturbations in the lower F region to spread F and plasma bubbles extending to much higher altitudes. Related efforts with correlative data are defining 6) the occurrence and locations of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, the 8) 2D (height-resolved) structures of plasma bubbles, and 9) the expected propagation of GWs and tides from the lower atmosphere into the thermosphere and ionosphere.

In aviation, satellite navigation is generally only used to determine the absolute position of aircraft. We show that the signals can also be used for safe relative navigation provided that a data link exists between the two aircraft. The link can be used to form a double difference combination of code phase measurements and determine a three dimensional baseline vector. The baseline vector is protected by protection levels which determine the 3×10−7 error bound of the baseline estimation. Thus, the distance vector can be used to perform safe approximation maneuvers in instrument weather conditions. We derive the protection level expression and test the baseline vector estimation using data from two real satellite navigation receivers on the ground. Moreover, we simulate an intercept mission using a Spirent GNSS7790 simulator and show that with the derived protection bounds an approximation up to 10 m is possible.

In this manuscript, we derive a concept for a four dimensional Required Navigation Performance by extending the existing lateral RNP into the vertical and along-track dimensions. Based on the target level of safety desired by ICAO and traffic on a given route, an along track requirement can be formulated for the traffic using the airway. In the vertical, accuracy requirements at the 99.5% level are already specified within the performance based navigation concept, however monitoring and alerting is not foreseen. Here, we suggest a monitoring technology based on satellite navigation that can also be used to ensure vertical separation in RVSM airspace.

Advancement in augmented satellite navigation enables a new class of instrument approach procedures for aircraft. These approaches are based on regional augmentation systems which broadcast corrections via a geostationary satellite. The enhanced GNSS navigation solution using the corrections from the satellite provides the necessary accuracy and integrity to perform approaches with vertical and lateral angular guidance to a given runway threshold. This enables cost effective and simple procedure generation with low descent minima even for small airports. Moreover, it supports high precision en-route navigation and future high precision flight guidance applications.

PurposeThe purpose of this paper is to show the performance during flight tests of the proposed GBAS Approach Service Type D navigation – intended to support autoland operations – in comparison to ILS.Design/methodology/approachAn experimental GBAS station was installed at the research airport in Braunschweig. Data processing complied with the currently proposed requirements to support automatic landings. Corrections for GPS measurements and integrity parameters were sent to a research aircraft which was equipped with an experimental GPS receiver providing raw measurement data. The received data and measurements were then processed on board in real‐time and provide approach guidance information to the experimental pilot in form of a flight director indication. To evaluate system performance the authors create a truth reference track from a post processed carrier phase solution. Finally, the GBAS outputs and the received ILS signals are compared to the truth reference.FindingsThe system performed well within all specifications and showed full availability at all times during the flight. Compared to ILS, GBAS is significantly more precise and shows almost no noise.Research limitations/implicationsThe navigation solution was flown manually according to flight director displays, therefore no automatic approaches and landings could be performed.Practical implicationsIt has been demonstrated that GBAS can support the intended operations under nominal conditions.Originality/valueThis work is part of the ongoing validation of the proposed standards for a satellite based landing system. It compares GBAS and ILS data from flight tests carried out with a representative aircraft.

Ionospheric fronts pose a significant threat to single frequency ground based augmentation systems (GBAS) for airplane precision approach. Here, we show our implementation of two ionospheric threat models in the DLR MASTER GNSS Simulator, a modified Spirent GSS7780/779. These threat models include the standard GBAS ”front” threat model as required for CAT-1 certification and a simplified plasma bubble model intended to represent equatorial conditions. These models can now easily be simulated at the German Aerospace Center's facilities. As an example, we simulate a GBAS ground facility (with a code carrier divergence monitor) affected by both a plasma bubble with a constant differential delay of −2 m and fronts of various gradients and speeds. Results confirm that a plasma bubble can lead to worst case position biases that may cause misleading and hazardously misleading information to be used by an approaching aircraft. Moreover, we confirm that ionospheric fronts at a speeds close to the airplane approach speed and propagating into the approach direction cause the most severe range biases. These, mapped to the position domain, can also cause hazardously misleading information.

Equatorial spread-F is a common occurrence in the equatorial ionosphere that is associated with large variations in plasma density that often cause scintillation and interference in communication signals. These events are known to result from Rayleigh–Taylor instability, but the day-to-day variability of their occurrence is not well understood. The triggering mechanism of plasma depletions is still a matter of debate, but may be linked to gravity waves that under favorable conditions propagate to the middle atmosphere. Understanding the triggering of ESF was the focus of the SpreadFEx campaign near Brasilia, Brazil in 2005. The campaign provided co-located airglow and GPS observations to study the onset of plasma depletions and their evolution as they traversed the region. Comparisons between the 630.0 nm airglow data and GPS data demonstrate the ability of the compact dual frequency GPS array to detect the plasma bubbles and retrieve reliable propagation characteristics of the depletions. In this case study, a plasma depletion was detected and moved over the array at velocities of 85–110 m/s, slowing as it moved towards the east. Correlation of consecutive airglow images gives consistent estimates of the eastward drift over the same time period. Mapping the airglow data to the GPS line-of-sight geometry allows direct comparison and reveals a resolvable westward tilt of the plasma depletion that may be due to vertical shear. The uniqueness of this study is the ability to resolve locally the characteristics of the plasma depletion without relying on assumptions about the mapping of the depletion along magnetic field lines to large latitudinal distances. It presents new information for understanding ESF development and the development of depletions strong enough to produce scintillation.

Ground Based Augmentation Systems (GBAS) for the precision approach of aircraft have never been so close to support automatic approach and landings under CAT IIIc conditions as they are today. However, as one key requirement for certification, it has to be demonstrated that the required integrity, continuity and availability allocations for GBAS are met, even under the most unfavorable circumstances. As for ILS/MLS, the performance of the total system (GBAS, the aircraft and its automatic landing system) is the key to eventual certification. Contrary to ILS/MLS-based guidance, at this moment no standard models and parameters for navigation errors and disturbances have been defined yet for assessing automatic landing performance based on GBAS. This raises the questions (1) how well does the integrated system perform with state of the art GBAS error models, and (2) for a given performance level reached with ILS/MLS, how much error could be tolerated when using GBAS instead? In this paper we have made a preliminary step to find an answer to the first question. To this end we have taken an existing, flight tested automatic landing system, tuned for use with DLRs fly-by-wire test bed ATTAS (Advanced Technologies Testing Aircraft System), which is representative for EASA Part 25-class aircraft. The landing system was adapted for use with GBAS and an advanced GBAS error model was incorporated in the simulation model. With this set-up, we performed the same Monte-Carlo simulations as were originally done with ILS. Initial results indicate that, based in the adopted error models, CS-AWO criteria can be met with more ease than with ILS/MLS-based guidance. It is expected that performance of GBAS-autoland systems can be further improved by exploiting new features that GBAS has on offer, tolerating larger NSE errors or possibly allowing operational autoland limitations, like maximum crosswind, to be relaxed

[1] Volcanic explosions or shallow earthquakes are known to trigger acoustic and gravity waves that propagate in the atmosphere at infrasonic speeds. At ionospheric heights, coupling between neutral particles and free electrons induces variations of electron density detectable with dual-frequency Global Positioning System (GPS) measurements. Using GPS data collected in the Caribbean, we identified an ionospheric perturbation after a major volcanic explosion at the Soufriere Hills Volcano (Montserrat, Lesser Antilles) on 13 July 2003. Spectral analysis reveals peaks centered at 1 and 4 mHz, similar to those in previous observations and consistent with theory, suggesting both gravity and acoustic wave components. We retrieve a horizontal velocity of ∼624 m/s for the acoustic component, which implies upward propagation at ∼33°, consistent with ray-tracing results. We model the acoustic wave using an N-wave pressure source at ground level combined with ray tracing to propagate the neutral pressure wave; this accounts for the dispersive characteristics of the atmosphere while conserving total acoustic energy. Plasma velocity is derived from neutral velocity using a finite difference solution of the magnetohydrodynamic momentum equation. The continuity equation for charge densities is used to compute corresponding electron density variations, which are then numerically integrated along satellite-to-receiver line of sights, simultaneously accounting for the satellite displacements. We minimize the misfit between observed and model waveforms to estimate a total acoustic energy release of 1.53 x 10 10 J for the primary explosion event at Soufriere Hills Volcano associated with the peak dome collapse. This method can be applied to any explosion of sufficient magnitude, provided GPS data are available at near to medium range from the source.

[1] It has been proposed that earthquakes are preceded by electromagnetic signals detectable from ground- and space-based measurements. Ionospheric anomalies, such as variations in the electron density a few days before earthquakes, are one of the precursory signals proposed. Since Global Positioning System (GPS) data can be used to measure the ionospheric total electron content (TEC), the technique has received attention as a potential tool to detect ionospheric perturbations related to earthquakes. Here, we analyze 2 years (2003–2004) of data from the Southern California Integrated GPS Network (SCIGN), a dense network of 265 continuous GPS stations centered on the Los Angeles basin, for possible precursors. This time period encompasses the December 2003, M6.6, San Simeon and September 2004, M6.0, Parkfield earthquakes. We produce TEC time series at all SCIGN sites and apply three different statistical tests to detect anomalous TEC signals preceding earthquakes. We find anomalous TEC signals but no statistically significant correlation, in time or in space, between these TEC anomalies and the occurrence of earthquakes in southern California for the 2003–2004 period. This result does not disprove the possibility of precursory phenomena but show the signal-to-noise ratio of a hypothetical TEC precursor signature is too low to be detected by the analysis techniques employed here. Precursors may still be revealed for future large earthquakes in well instrumented areas such as California and Japan, if the tests can be developed into techniques that can better separate external influences from the actual TEC signal.

The recent publication of the advanced Required Navigation Performance (RNP) specifications enable constantly precise aircraft path guidance without demanding expensive equipment and crew certification from the operator. Combined with the operational roll-out of satellite based regional augmentation for Global Navigation Satellite Systems (GNSS), it enables new possibilities such as implementing instrument approach procedures at airports, whose location previously forbade such. Here, we design and flight test two advanced RNP procedures at the airports of Saarbrucken and Egelsbach containing a fixed radius turn which terminates at the final approach fix of a 3D guided final. Results show that the track can be followed with a precision of below 0.1 nautical miles both in manual and in automatic flight with a light piston twin aircraft and with a fast business jet. Effectively, the procedures presented in this paper decouple Saarbrucken airport from French airspace and Egelsbach airport from the high density traffic of the Frankfurt (Main) International control zone.

We provide here an overview of, and a summary of results arising from, an extensive experimental campaign (the Spread F Experiment, or SpreadFEx) performed from September to November 2005, with primary measurements in Brazil. The motivation was to define the potential role of neutral atmosphere dynamics, specifically gravity wave motions propagating upward from the lower atmosphere, in seeding Rayleigh-Taylor instability (RTI) and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12, and the GUVI instrument aboard the TIMED satellite. Initial results of our SpreadFEx analyses are described separately by Fritts et al. (2009). Further analyses of these data provide additional evidence of 1) gravity wave (GW) activity near the mesopause apparently linked to deep convection predominantly to the west of our measurement sites, 2) small-scale GWs largely confined to lower altitudes, 3) larger-scale GWs apparently penetrating to much higher altitudes, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent influences of these perturbations in the lower F-region on the formation of equatorial spread F, RTI, and plasma bubbles extending to much higher altitudes. Other efforts with SpreadFEx data have also yielded 6) the occurrence, locations, and scales of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, 8) 2-D (height-resolved) structures in electron density fluctuations and equatorial spread F at lower altitudes and plasma bubbles above, and 9) the occurrence of substantial tidal perturbations to the large-scale wind and temperature fields extending to bottomside F-layer and higher altitudes. Collectively, our various SpreadFEx analyses suggest direct links between deep tropical convection and large GW perturbations at large spatial scales at the bottomside F-layer and their likely contributions to the excitation of RTI and plasma bubbles extending to much higher altitudes.

In order to assess the integrity risk for GBAS based automatic approach and landing, we investigated a total performance concept of a combined system consisting of an ILS look-a-like GBAS landing system (GLS) and a DeHavilland Dash-2 Beaver aircraft. We propagated four basic pseudorange errors to a position error distribution, which was then the source of position uncertainties for the GLS installed in the aircraft. Results show that the vertical total system error (TSE) in the steady state final approach lags behind the vertical navigation system error (NSE). The TSE is smoothed and preserves the general temporal sequence of the error. A reduction of 30\% of the TSE standard deviation with respect to the NSE only occurs during a period of glide slope overshoot, where the autopilot uses large and steadily declining elevator deflections to return to the desired glide path. With minor adaptations this concept can be refined and a possible error reduction may be achieved.

The German Aerospace Center (DLR) operates small drones i.e., octocopters for research purposes at different institutions at different locations. In addition, the DLR is working on the integration of drones into unsegregated airspace in several national and international projects. One of the key elements for a safe integration of drones is the positioning capability of the air vehicle. On the one hand it is required for geofencing applications in order to create no-fly zones and on the other hand it is required to generate an airspace management for unmanned traffic. In recent years, the Performance Based Navigation (PBN) concept was introduced for manned aviation to exploit the navigation performance of modern satellite navigation and to manage the available airspace. One approach for Unmanned Aircraft System (UAS) Traffic Management (UTM) is obviously to transfer the PBN concept for drone applications. However, as drones usually use commercial off the shelf equipment that is usually not certified for aviation applications, the question is how the basic principle can be transferred. In this work, we used a commercial octocopter (MikroKopter MK Okto XL 6S12 ARF) to assess the horizontal Navigation System Error (NSE) as well as the lateral Total System Error (TSE) while using different GNSS receivers. The horizontal navigation is based on GNSS in stand-alone mode or using SBAS augmentation and a compass for directional information aid. No additional sensors like inertial measurements are used here. We are going to present the results from flight trials with two different GNSS receivers and will draw conclusions for a PBN concept for drones.