ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)[EN­005] GBAS CAT II/III concepts for flexible approach procedures(EIWAC 2010)+

T. Feuerle*, M. Bitter*, P. Hecker*, R. Geister***Institute of Flight GuidanceTechnische Universitaet Braunschweig
Braunschweig, Germany[t.feuerle | mark.bitter | p.hecker]@tu-braunschweig.de**German Aerospace Center
Institute of Flight GuidanceBraunschweig, Germany
robert.geister@dlr.de

Abstract: Satellite based Navigation Systems (Global Navigation Satellite System GNSS) will become a major element in
the navigation infrastructure of the future. In addition to classical en-route and terminal navigation, where GNSS is
increasingly used, approach and landing procedures are being developed and implemented based on GNSS. To meet therequirements of integrity, accuracy, continuity and availability for precision approach and landing operations, augmentation
systems are needed. Currently there are two augmentation systems for these periods of flight available: Ground Based
Augmentation Systems (GBAS) and Space Based Augmentation Systems (SBAS). This paper will focus on GBAS research
projects conducted by the Technische Universität (TU) Braunschweig, Institute of Flight Guidance (IFF), and the German
Aerospace Center (DLR) Braunschweig, Institute of Flight Guidance (FL). While TU Braunschweig is working mainly inthe domain of navigation technology (both ground and airborne) DLR (namely Robert Geister) is concentrating on theprocedure design and implementation of special approach procedures.
In December 2008 DLR has installed an experimental GBAS ground station, manufactured by Thales ATM GmbH. The
station has a production-line software status but will not be used for operational approach procedures inboundBraunschweig airport. Therefore experimental procedures can be implemented easily.
Furthermore a Galileo Test Environment called “aviationGATE” is currently under development by TU Braunschweig,
using a total of 9 ground located transmitters to cover an area of up to 5,500 square-kilometres. A concept has been
designed which includes among others the implementation of an aircraft positioning module and an aviationGATE
correction message uplink module. With the coverage area including the airport as well as the already implemented GPS
and GBAS approaches this test bed will serve as an ideal environment for tests of GBAS CAT II/III dual constellation
concepts. This paper will describe the setup of the GBAS research infrastructure at the Research Airport BraunschweigWolfsburg. Furthermore an initial set of GBAS approaches with different glide path angles will be discussed.
Keywords: GBAS CAT II/III, approach procedures, airborne augmentation
the IFF. In April 2010 he finished his PhD-Thesis called“GPS- and Ionosphere Monitoring with Low-Cost GPS
Receivers”.

1. BIOGRAPHY
Thomas Feuerle received his Diploma (Dipl.-Ing.) inmechanical engineering in 1997. He joined the Institute of
Flight Guidance (IFF) of the Technische Universität
Braunschweig in May 1997 as a technical pilot of theresearch aircraft Dornier Do 128-6. He has been involvedin the recent GBAS activities at the Institute. Besides the
GBAS hardware installation and the adoption of the realtime software onboard the aircraft he flew most of the
GBAS experimental approaches with the Dornier. He is
also responsible for the GBAS data evaluations as well as
for the development of GBAS software tools at theInstitute. Since 2005 he is team leader of the ATM team at

Mark Bitter holds a Dipl.-Ing. in mechanical engineeringand is employed as a research engineer at the Technische
Universität Braunschweig, Institute of Flight Guidance
since 2003. He is member of the flight metrology
department and as flight test engineer of the research
aircraft Dornier Do 128-6 he is responsible for hardware
development, adaption, installation and operation ofexperimental equipment onboard the aircraft.
Prof. Peter Hecker joined the Institute of Flight Guidanceof the German Aerospace Center DLR 1989 as researchscientist. Initial focus of his scientific work was in the261

T. Feuerle, M. Bitter, P. Hecker, R. Geister
equipment as well as components for a GBAS groundstation. One attempt that has been pursued to increase theperformance of a GLS with respect to the high CAT-II/III
requirements is to implement independent monitors andadditional augmentation systems, one of them being anaircraft based augmentation utilizing an Inertial Reference
System (IRS). The inertial part of an integrated system isable to assure the continuity of the GLS for a certain time
span. In contrast to stand-alone GNSS navigation, theGBAS corrected pseudoranges have to be smoothed andcannot be used for the navigation solution immediately
after acquisition. Thus, GBAS operations are relatively
vulnerable to shadowing. Concerning integrity aspects,
integration with inertial navigation using Aircraft
Autonomous Integrity Monitoring (AAIM) can achieve ahigher ability to detect GNSS faulty measurements which
are caused on user level like rare ionospheric events andthus cannot be augmented by the GBAS ground station.
Within the German UniTaS IV project, founded by theFederal Ministry of Economics and Technology (BMWi)
and administered by the Agency of Astronautics of the
DLR, an experimental on-board equipment has beendeveloped and different levels of integration of GBAS andinertial navigation system with respect to accuracy,
continuity in case of GNSS outage and on-board integrity
monitoring have been evaluated.

field of automated situation assessment for flight guidance,
where he was responsible for several research projects.
From 2000 until 2005 Prof. Hecker was head of the DLR
Department “Pilot Assistance”. Since April 2005 he isdirector of the Institute of Flight Guidance of theTechnische Universität Braunschweig. He is managing
research activities in the areas of air/ground co-operative
air
traffic
management,
airbornemeasurement
technologies and services, satellite navigation, humanfactors in aviation and safety in air transport systems.
Robert Geister graduated from the Technical University of
Hamburg Harburg as a Dipl. Engineer in Computer
Science Engineering in 2005. Since then he is employed in
the Institute of Flight Guidance of the German Aerospace
Centre in Braunschweig. He graduated from the National
Test Pilot School’s short course (Mojave, CA) as a flighttest engineer in 2009. At the German Aerospace Centre heis currently working there in the areas of flight testing,software development, and operational procedures basedon GBAS.
2. INTRODUCTION
In contrast to area navigation (RNAV) based on GNSS,
precision approach and landing operations need additional
augmentation to meet the requirements of integrity,
accuracy, continuity and availability. Ground Based
Augmentation Systems (GBAS) are designed to support
precision approach operations at airports. They offer more
flexibility than the well approved Instrument Landing
System ILS as they can provide desired flight pathinformation for approaches, landings, missed approaches
and flight paths through the terminal area. The GBAS
ground station receives the signal in space and determines
the ranging source errors based on measurements frommultiple ground reference receivers. These errors arebroadcasted via VHF Data Broadcast (VDB) to the aircraftin the coverage area and used on-board for correcting theranging sources. Additionally, the signal integrity ismonitored and parameters are computed which are needed
for the determination of the availability of the signal inspace for a desired level of service. The VDB message
link also includes information on the Final Approach
Segment (FAS).

Until now, the evaluation of the developed integrated
GBAS/INS system and the on-board integrity monitoringhas been based on artificial errors that were introduced onrecorded flight trial data in post-processing. The
introduction and use of a Galileo test environment that will
be explained below will open up new possibilities forresearch under real-time conditions. It will enable various
options to concretely manipulate signals emitted and test
its impact on the whole system as well as it will serve as
an ideal environment for tests of GBAS CAT II/III dualconstellation concepts.
A Galileo test bed called aviationGATE is being set up at
the Braunschweig Research Airport to enable aviation
related technologies to be developed and tested in arealistic scenario. The aviationGATE is being built by the
IFF as part of the already mentioned project UniTaS IV.
Measuring 5,500 square kilometers in extent and up to 100
kilometers across, aviationGATE is unique and enables
aircraft to receive Galileo signals during their entire
approach to Braunschweig Research Airport.

Ground Based Augmentation Systems that provide
approaches equivalent to ILS CAT-I operations are almost
certified for operational usage. Future GNSS Landing
System (GLS) CAT-II/III operations have to meet more
severe requirements of integrity, accuracy, continuity andavailability. On ICAO level the requirements for thesesystems are currently under development.

A total of nine dual frequency pseudolites (PSL) provide
the complete test bed with signals. While five of the nine
PSLs are located on the area of the airport, the remaining
four PSLs are arranged on elevated positions with adistance of up to 70 km to the airport. This subdivision
into an inner and an outer ring ensures that signals can bereceived in the entire area with a minimum coverage offive PSLs. The aviationGATE uses the E1 and E5
frequency bands with both messages (I-NAV, F-NAV) on

The IFF has been conducting a lot of research on this topic
and several ground and flight tests have been performed in
the past. Ongoing activities are covering on-board

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E5. Each signal can be adapted, changed to vary or freely
define its navigation message, to change its
synchronization in relation to GPS, to other PSLs or to theother signal emitted on the same PSL. In particular, thereis the possibility to generate offsets between E1 and E5 asneeded for test purposes. This can be done relying on thetiming equipment used in each PSL, but also can bemonitored by two reference stations at different positions.
At the current state, the inner ring of the aviationGATE isfully operational, while the outer ring is not able to send
synchronized signals, yet.

2.1 Interoperability Trials Braunschweig
Testing the Russian GBAS system presented different
challenges from those encountered previously. Both theWestern European and the US systems are the fruit of along development history based on a US initiative andhave thus many shared requirements, including the use of
EUROCAE and RTCA MOPS (Minimum Operational
Performance Specifications). The Russian system covers
the use not only of GPS, but also of GLONASS – which
for GBAS is included in ICAO Annex 10, but not in the
different MOPS. The design was started independently,
using MOPS only where Annex 10 needed completion todefine functionality.

For the intended purpose as a test environment for dualconstellation GBAS concepts, the aviationGATE has to befurther developed (see chapter 4). During GLONASS/GPS
dual-constellation data gathering campaigns andinteroperability trials performed 2007 [1] in Braunschweig
and 2009 [2] in Moscow, different experiences have been
gained and will be taken into account. Existing
components of the ground segment as well as componentsof the user segment will be modified and extended. Firstly,
ranging source errors of each PSL signal have to be
determined and broadcasted. As the VDB data link of the
GBAS ground station at the Braunschweig Research
Airport cannot be adapted directly, a concept fortransmission of the increase in correction data via VHF
data link in relation to a single constellation will benecessary. Secondly, the experimental GBAS/INS onboard equipment will be extended to receive
aviationGATE pseudoranges and correction data. Also the
GBAS/INS navigation algorithms and the calculation of
the hybrid protection levels will be adapted.

Fig. 1: GBAS ground station and monitor installation

Fig. 1 provides an impression of the ground systeminstallation of the LCCS-A-2000 station combined with anindependent GBAS ground monitor (developed by theInstitute of Flight Guidance, TU Braunschweig).

The before mentioned interoperability trials have been
initiated by EUROCONTROL due to the fact that thetechnical complexity of satellite-based systems is such thatdifferent interpretations of standards cannot be excluded.
In principle, equipment interoperability is guaranteed by
the development and validation of the ICAO SARPS andcomplemented by industry standards, such as RTCA and
EUROCAE MOPS, ICD’s and ARINC standards. Theseshould be detected and clarified as quickly as possible.

The first set of trials showed no ability to decode othersystem’s signals. The investigation revealed that Annex 10
defines navigation data to be modulated “in amathematically positive sense” onto the signal – a wordingthat was interpreted differently in Russia. In the MOPS,
different, unambiguous wording had been used and asconsequence an update to Annex 10 has been proposed
and accepted to clarify the modulation.
Other results include the necessity to adapt processes offrequency coordination between European states, as thedigital, timeslot based GBAS system allows several
stations in close proximity (in this case Bremen andBraunschweig – Fig. 2) to transmit on the same frequency.
This is possible, as each station will only use 2-3 of the 8available timeslots and the standards foresee appropriate
distinction mechanisms. In these times in Germany only
one frequency was available for GBAS use. However,depending on topography, altitude and antenna installation,practical reception ranges are 200-250NM. The
transmission areas of the three stations in Germany thus263

T. Feuerle, M. Bitter, P. Hecker, R. Geistershow a clear overlap and ICAO has defined a 500NM
coordination radius [1].

Fig. 3: Mobile GBAS test equipment

A detailed evaluation of the test can be found in [2].
The evaluation and the fact that the data was received by
all systems tested without anomalies have shown that thetechnical standards are robust. The trials have also served
to address operational aspects and open discussions took
place with the many actors involved in operational use ofsuch a multi-constellation system. The elements to beconsidered range from ownership and training
considerations for operators of a fleet using mixed
equipment, and for ground system operators to thenecessity of validation of GPS and GLONASS
performance and notably integrity separately during theprocedure development process. Also addressed was the
ATC impact of providing consistent service to a mixed
fleet equipped without GBAS, with only GPS or withmulti-constellation systems and the phraseology necessary
to unambiguously describe the requested service.

Fig. 2: Location of GBAS stations in Germany (note the 500 NM
frequency coordination radius)

2.2 Moscow Trials
Based on the broad experience of GBAS related projects at
TU Braunschweig a mobile measurement equipment setup
had been developed. As it can be seen in Fig. 3 an adapter
for the connection of a Rockwell-Collins Multi-ModeReceiver to a laptop with ARINC PC Card had been
worked out. With the laptop all online parameters of theMulti-Mode-Receiver (like channel number) can bechanged. For the MMR specific hardwired configurationof parameters, a connector-integrated switch board had
been implemented. With this special feature it is easy tooperate with different versions of the MMR GLU 925, likethe version -430 (Airbus) or -330 (Boeing). Additionally, a
VDB receiver (manufactured by the French company
Telerad) had been repackaged. The purpose of this rebuild
was that all parts of the mobile GBAS measurement
equipment will fit into one or maximum two small piecesof luggage which can be taken into the cabin of acommercial airliner. To assure the proper working of theTelerad VDB Receiver, cabling between the MMR and thereceiver is also provided to support using a PPS (PulsePer-Second) input coming from the built-in GPS receiverof the MMR and synchronizing the timing of the VDB
receiver.

The focus at the Institute of Flight Guidance has now been
turned to more complex integrated systems and thevalidation of future modifications and extensions of GBAS
standards, such as GAST-D and the future multiconstellation, multi-frequency GBAS system designs.
3. AIRBORNE EQUIPMENT
As part of the project UniTaS IV, a concept for an
integrated GBAS/INS system has been developed that
finally resulted in the realization of an experimental onboard system. Centerpiece of this system – next to theinertial measurement unit (IMU) – is the GBAS/INS
integration unit designed by Funkwerk Avionics GmbH(see Fig. 4). It incorporates GNSS receiver, VDB receiver,
GBAS computer and integration computer. The INS datais fed to the system externally via serial interface.

The first measurement campaign with this portablemeasurement equipment took place in April 2009 in
Moscow.

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correction, the time difference between the current time
and the time of applicability of the corrections andtropospheric correction.

Fig. 4: GBAS/INS integration unit (Funkwerk Avionics)

The GNSS receiver provides pseudoranges and carrier
phase measurements while the VDB receiver provides
pseudorange- and range-rate corrections that the GBAS
computer first decodes and then adapts to the smoothed
pseudoranges. Afterwards, the integration computer
applies the GBAS navigation algorithms on GBAS dataand inertial data and calculates the hybrid protection levels
for the integrity monitoring function.

Fig. 5: Hybridization of GBAS with INS

During the update of the KALMAN Filter, the system stateis corrected by the differences between the GBAS
corrected pseudoranges and the estimated pseudoranges.

A short introduction to the general principle ofhybridization and integrity monitoring will be given in thefollowing two chapters. More detailed information can befound in Fehler! Verweisquelle konnte nicht gefunden
werden..

3.2 Integrity Monitoring
Beside the ability of coasting during temporary signal loss,
inertial measurement units provide the augmentation of thedifferential corrected GNSS signal on user level. Locally
disturbed ranging sources can either be excluded from thehybridized navigation solution or be accounted by thecalculation of the protection levels [7].

3.1 Hybridization
The hybridization of the GBAS with the inertial part isdone within a full-state (or total-state) KALMAN Filter.
This means that the position, velocity and attitude
information is directly calculated by the filter instead of
estimating the errors in position, velocity and attitude.

The principle structure of the implemented integrity
monitoring is depicted in Fig. 6. The basis for the fault
detection and the fault exclusion functions is a mixture
between the techniques proposed in [7] and [8].

The state vector of the system contains position, velocity,
attitude and heading as well as the estimation of the sensor
bias, i.e. the accelerometer bias and the gyro bias, and in
addition, the estimation of the receiver clock errors (e.g.
by estimating the clock bias). The navigation solution is
obtained by solving the navigation equations of the inertial
part directly within the propagation step of the KALMAN
Filter. Thereby, the differential equations for the attitude,
the velocity and the position are solved. As it is depicted inFig. 5, the inertial and the GNSS information are fed into
the navigation filter. The inertial data can be optionallycomplemented by barometric data.

The GNSS, INS and optionally the barometric data (Air
Data Reference, ADR) are fed into the system. Dependingon the service availability, the GNSS data can be eithersole GPS or SBAS/GBAS corrected raw data. One main
filter (MF) uses all (n) available GNSS ranging sources,
while a bank of n-1 sub-filters (SFi) is operated in parallel.
Each sub-filter is excluding one ranging source. Fault
detection is either performed by monitoring the main
filter’s residuals comparable to the method proposed in [8]or by monitoring the solution separations in the horizontal
and vertical domain between the main filter and the subfilters. If a fault is detected, the healthy subfilter – the onethat is excluding the faulty ranging source – is used toreset the whole system. The fault-free protection levels are
extracted from the main filter’s error covariances. The
missed-detection protection levels are derived from main
filter and sub-filter characteristics. As for the sole GBAS
protection levels, the maximum of either fault-free or
missed-detection protection levels is taken for horizontal
or vertical protection level information. Additional filter

Within the measurement update step of the KALMAN
Filter, the GBAS-corrected pseudoranges are used to aid
the inertial part. For the smoothing of the pseudorange ρithe carrier phase measurement Φi is used as defined in [6].
According to GAST D requirements, two solutions arecalculated with a smoothing time constant of 100 seconds
and 30 seconds respectively.
If the pseudorange-corrections (PRC) and range-ratecorrections (RRC) are valid, they are applied to thesmoothed pseudoranges as well as satellite clock265

T. Feuerle, M. Bitter, P. Hecker, R. Geister
Furthermore, there are thoughts to use only theaviationGATE components to evaluate parts of currently
discussed GAST-D concepts. In this approach, airborne
monitor schemes, for example, can be evaluated wheninserting errors on one of the ranging sources of theaviationGATE while the ground segment still transmits
correction data as before.

banks are used for monitoring newly acquired ranging
sources before they are used for navigation. Also,
excluded ranging sources are further monitored inseparated filter banks.

A depiction of the layout principles of the dualconstellation test bed at the research airport ofBraunschweig can be found in Fig. 7. The chosen
approach consists of the ground and user segment, theaviationGATE PSLs and the GPS constellation. The
aviationGATE PSLs will be controlled by the groundsegment. In the control station of the aviationGATE
pseudorange and range-rate corrections for the PSL signals
will be generated. Another module will receive the GPS
GBAS corrections, coming from the GBAS station at
Braunschweig Research Airport. These GPS andaviationGATE corrections will be merged and uplinked
via a special data link to the user segment on board of anaircraft. The approach of using not a conventional VDB
data link has the drawback that no statement about theappropriateness for dual-constellation GBAS of a VDB as
described in the standards can be made. But it gives us
flexibility in terms of research and allowance of datatransmission, because an already available telemetry will
be used.

Fig. 6: Hybrid integrity monitoring

4. Expansion of aviationGATE Towards a Test Bed
for Dual-Constellation GBAS Research
As mentioned before, the aviationGATE will be further
developed to be used as an environment for dualconstellation GBAS research and research on GBAS
system concepts (like GAST-D, for example). The main
modification of the aviationGATE is the implementationof the GBAS component using the Galileo signals of thepseudolites. The basic idea to conduct dual-constellation
research is to have one space-based constellation (GPS)combined with the aviationGATE constellation. The
reason behind this is the hypothesis that all PSLs are able
to send navigation signals. Ranging source errors caneasily be inserted on any PSL signal which then has to be
determined on board the approaching aircraft. Two
different modes are planned:
1.

2.

a dedicated ranging source will be disturbed andthe respecting error will be transmitted (i.e.
detected) by the ground station to the approachingaircraft

Fig. 7: System concept of a test bed for dual-constellation GBAS
researcha dedicated ranging source will be disturbed andthe respecting error will not be transmitted (i.e. an
undetected error on ground side)

The user segment on board of an aircraft will receive threedifferent kinds of data:

With these two different modes on ground station side theairborne equipment can be tested whether it will apply thetransmitted corrections in an adequate way or whether the
on-board monitors (like the before mentioned hybrid
integrity monitoring) are able to detect the inserted errors.
So far, this testing had been done offline with error
simulations fed in into a navigation system. With theintended expansion, additional hardware-in-the-loop-tests
are planned.

•

GPS satellite signals•

aviationGATE pseudolite signals•

combined correction data

The received data blocks will be combined in the
proprietary experimental GBAS software. Different
integrity monitoring approaches are already implemented(see e.g. the hybrid integrity monitoring) which are

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calculating a navigation solution as well as hybrid
protection levels. Due to its modular composition
additional concepts will follow.
5. APPROACH PROCEDURESAs the international air traffic becomes more and more
complex (a growth of 2.3% from 2006 to 2007, 57% from1997 to 2007 [11]) there is a growing demand for new
operational procedures. Especially quiet and fuel efficientapproaches are desired. GBAS provides more flexibility
than current precision landing systems. Therefore, it isidentified as a potential key technology for providing
different approach procedures tailored for unique demands
at a special location. Particularly steep precision
approaches have a high noise reduction potential as theaircraft can stay at a higher altitude for a longer time. Thiseffect is amplified by air vehicles capable of Short TakeOff and Landing (STOL) procedures.

Fig. 8: 5.5° (red) and 3.5° (green) approach path inbound EDVE
Fig. 9: GLS Approach Chart

During this work approach procedures based on GBAS
with slightly higher glide path angles than usual (4.5° 5.5° instead of 3° - 3,5°, see Fig. 8) were investigated.
Therefore a simple software simulator of a MMR was
created and integrated into a Generic Experimental
Cockpit (GECO) simulator. The FAS data for an ILS lookalike approach (glide path angle 3.5°) and for approacheswith steeper glide path angles were validated in thissimulator. Pilots were familiarized with the new
approaches in the simulator and some questionnaires werefilled out regarding the workload and flight technicaldemands for the pilots.

Fig. 9 shows one of the approach charts designed for the
airport Braunschweig-Wolfsburg. The approach chart isbased on a published [9] GPS (RNAV) procedure for
runway 26. The horizontal profile is exactly the same as in
the case of an RNAV approach but the final approach isconverted into a precision approach. Additionally, thevertical profile is adapted for each Glide Path Angle(GPA). All approaches (even though they have different
GPA’s) have a Threshold Crossing Height (TCH) of 50ft.
This leads (due to the different GPA’s and the unchanged
position of the Final Approach Point (FAP)) to different
intercept altitudes before the final descend. In the provided
example the final approach starts at an altitude of 3,100ft
Mean Sea Level (MSL). A GPA of 5.5° results in anintercept altitude of 3,700ft MSL accordingly.

After the GBAS Landing System (GLS) approaches werevalidated in the simulator the FAS data blocks weretransferred into an actual ground installation at the
research airport Braunschweig-Wolfsburg. The FAS data
was checked with ground trials and some flight trials wereconducted to verify the data gathered in the simulator
trials.

In the upper left corner the Reference Path Identifier(RPID) is depicted. The simulator trials showed that it ispracticable to integrate the runway number in the RPID.
The first letter is always “G” to indicate a GLS approach.
The fourth letter is a unique letter for each runway
direction. The letters C, L, and R are omitted as it mightlead to confusion if multiply runways for one landing

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T. Feuerle, M. Bitter, P. Hecker, R. Geister
direction are present. In the middle of the approach chart
the RPID is shown with the according channel number thatis used to tune the approach with the desired flight path.
On the lower part of the approach chart the vertical profileof the approach procedure is shown. The GPA and thecheck altitudes are depicted. The tables are adapted foreach GPA.
As the underlying RNAV approach is a non-precision
approach, the charted obstacle clearance altitudes/heights(OCA/H) are higher than those for a precision approach.
For simplicity the altitudes were conservatively
maintained. For the flight trials the OCH was used as thedecision height (DH) for all approaches.
The approach procedures are very close to the procedures
described in [10] and therefore very easy to integrate into
the existing Air Traffic Management (ATM)infrastructure. The design principle to keep the horizontal
profile and the lateral positions of the navigation fixes
constant is presumed to keep the situation awareness level
for air traffic controllers and the pilots as high as possible.

Fig. 10: Altitude (MSL) over Time

Fig. 10 shows the vertical profile that occurred during one
test flight. It can be seen that the approaches with different
GPA’s had different intercept altitudes.

6. FLIGHT TRIALSOne of the purposes of the flight trials was the verificationof the results obtained in the simulator regarding pilot’s
acceptance and workload. Therefore, the approaches wereconducted similar to the ones conducted in the simulator.
Due to the architecture of the test system the tuning of theMulti Mode Receiver (MMR) during the flight trials wasdone by the cabin crew and the display of the deviation
signals was slightly different. The deviations weredisplayed on the Course Deviation Indicator (CDI) during
the flight trials whereas they were displayed on an
experimental primary flight display and navigation display
during the simulator trials.

Fig. 11: Horizontal Deviation (3.5°) over time

The approaches were set up at the initial or intermediatesegment in the appropriate altitude. From there the final
approach has been conducted manually, following thedisplayed deviations on the CDI. The evaluation pilots
stated that the workload was not rising excessively during
the steep approaches. There was a noticeable rise of therequired attention for a steep approach but the overall levelremained in a tolerable state.
Another purpose of the flight trials was the validation of
FAS data in the ground station and the verification of theoperability of the designed procedures. It was discoveredthat the procedures were not demanding with the type of
aircraft used. The approach speed was small enough tokeep the vertical velocity on a reasonable level.

Fig. 12: Horizontal deviation (5.0°) over time

Fig. 11 and Fig. 12 show the rectangular horizontal
deviations observed during an approach with a GPA of268

ENRI Int. Workshop on ATM/CNS. Tokyo, Japan. (EIWAC 2010)
3.5° (Fig. 11) and with a GPA of 5.0° (Fig. 12). It can beseen that in both cases the deviation decreases gradually
after intercepting the localizer. In the last 100 seconds ofeach approach, the deviations are well within 40m during
each approach.

Fig. 15: Vertical Deviation (5.5°) over time

7. CONCLUSIONS
Concluding, no problems during GBAS guided steep
approaches with this type of aircraft were encountered.
The fact that they can be flown manually with a nonstandard display of the deviation signals is very promising
for air taxi applications with similar types of aircraft oraircraft that have specific engine and aerodynamic
properties tailored for steep approaches. Further tests will
be carried out to investigate the system usability and theworkload of different pilots with different types of aircraft.
Additionally, the flare for an actual landing has to befurther investigated.

Fig. 13: Vertical Deviation (4.5°) over time

The paper has also described the layout of theexperimental airborne and ground installations at the
Research
AirportBraunschweig-Wolfsburg.
The
combination of a state-of-the-art GBAS ground station
with additional research installation forms a perfectenvironment for investigations on flexible approachprocedures. In a joint effort within the national funded
project “Bürgernahes Flugzeug” the both Institutes of
Flight Guidance at DLR and TU Braunschweig areworking closely together. Further trials are intended toinvestigate novel approach procedures (segmented and/or
steep
approaches)withanexperimental
GPS/aviationGATE on-board unit. With this combination
detailed research on fault-detection-and-exclusion on
dedicated failure scenarios can be accomplished in arealistic and close-to-operation environment.

Fig. 14: Vertical Deviation (5.0°) over time

Fig. 13, Fig. 14 and Fig. 15 show the rectangular verticaldeviations encountered during an approach with a GPA of
4.5° (Fig. 13), a GPA of 5.0° (Fig. 14) and a GPA of 5.5°
(Fig. 15). The results show that the deviations behave
similarly. The approaches were flown slightly below thedesired glide path but even though they were manually
flown it was managed to keep the deviations within arange of 10m as soon as a steady descend was established.
The pilots reported a steady behavior of the displayed
deviation signals and no increased workload during the goaround. The results show that no significant height loss
was given during the go around after a steep approach.
This reflects the results obtained in the simulator quite
well.

8. ACKNOWLEDGMENTS
The authors like to thank different people involved in the
different trials described in the paper. Special thanks aregoing to Andreas Lipp (EUROCONTROL) for his

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T. Feuerle, M. Bitter, P. Hecker, R. Geister
financing and support of the interoperability trials. Also
we would like to acknowledge the help of the flight test
crew at the IFF and Andreas Grüttemann (DLR) for his
certification support of the flight test equipment.

Proceedings of the 21st International Technical
Meeting of the Satellite Division of the Institute ofNavigation, 16-19, September 2008, Savannah,
Georgia, pp. 2920-2928

The technique of GBAS/INS integration and the data
shown in this paper are developed and collected during the
IFF’s
UniTaSIV
Project
fundedbytheBundesministerium für Wirtschaft und Technologie(BMWi) administered by the Agency of Aeronautics of the
DLR in Bonn (FKZ 50 NA 0734). Also the aviationGATE
is developed within the UniTaS IV project.

[6] -, “Minimum Operational Performance Standards for

GPS Local Area Augmentation System Airborne
Equipment”, RTCA Do-253C, RTCA Dec 2008
[7] M. Steen, M. Kujawska and P. Hecker, “Integrated

GBAS/INS Navigation System – Continuity andIntegrity Aspects”, Proceedings of the Symposium
Gyro Technology 2009, Karlsruhe, Germany[8] M. Steen and P. Hecker, “GBAS/INS Navigation

System: Further Developments of On-Board Integrity
Monitoring”, Proceedings of the 2010 International
Technical Meeting of the Institute of Navigation, ION
ITM 2010, San Diego, CA, pp. 386 – 393

9. REFERENCES[1] A. Lipp, T. Feuerle and P. Hecker, “Interoperability

Trials of GBAS Equipment”, Proceedings of the 13th
European Navigation Conference, ENC-GNSS 2008,
Toulouse, France[9] DFS.

DeutscheFlugsicherung,
DFS
Luftfahrthandbuch
Deutschland(Aeronautical
Information Publication, 2010[2] T. Feuerle, U. Bestmann, M. Steen, B. von Wulfen, P.

[10] ICAO. Doc 8168, Vol I, Procedures for

Air
Navigation Services, Aircraft Operations, Flight
Procedures, International Civil Aviation Organisation(ICAO), 2006

Hecker and A. Lipp, “Preparation for Upcoming
Multi-Constellation
GBAS
Systems”,
TU
Braunschweig, EUROCONTROL, Proceedings of the
22nd International Technical Meeting of the Satellite
Division of the Institute of Navigation, ION GNSS
2009, Savannah, Georgia, pp. 1169 – 1174

[11] German Aerospace Centre. Luftverkehrsbericht 2008[3] M. Bitter, T. Feuerle, B. von Wulfen, M. Steen, P.

10. COPYRIGHT

Hecker, “Testbed for Dual-Constellation GBAS
Concepts”, Proceedings of the IEEE/ION PLANS
2010, Indian Wells/Palm Springs, CA, pp. 680 – 687

The authors confirm that they and their institution holdcopyright of all original material included in their paper.
They also confirm they have obtained permission, fromthe copyright holder of any third party material included intheir paper, to publish it as part of their paper. The authors
grant full permission for the publication and distribution of
their paper as part of the EIWAC2010 proceedings or as
individual off-prints from the proceedings.

[4] European

Space Agency / European GNSS
Supervisory Authority, "Galileo Open Service, Signal
In Space, Interface Control Document", OS SIS ICD,
Draft 1, 2008[5] M. Steen, T. Feuerle, U. Bestmann, M. Stanisak and

P. Hecker, “Continuity and Integrity Aspects of an
Integrated
GBAS/INS
Navigation
System”,

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