TY - CONF T1 - An EGNOS Based Navigation System for Highly Reliable Aircraft Automatic Landing T2 - ENC GNSS 2009 PROCEEDINGS Y1 - 2009 A1 - DE LELLIS, E A1 - CORRARO, F A1 - CINIGLIO, U A1 - GAGLIONE, S A1 - CANZOLINO, P A1 - GARBARINO, L A1 - NASTRO, V AB -
Highly precise navigation is the core technology 
required for many applications, such as automated 
aerial refuelling (AAR), sea-based joint precision 
approach and landing systems (JPALS), stationkeeping, unmanned aerial vehicles (UAV) swarming 
and formation flight and unmanned ground vehicles 
(UGV) convoys. Advances in the above mentioned 
technology are possible considering the future 
GNSS framework, given that adequate 
characterization of new GNSS devices are 
performed and that new algorithms are developed 
that fully exploits the functionalities made available 
by the future GNSS systems. In this paper both 
aspects are considered, with specific reference to the 
use of GPS/EGNOS for reliable fixed wing aircraft 
automatic landing applications. 
For what concern experimental characterization of 
the satellite based navigation system GPS/EGNOS, 
the main aim of the activity was to describe the 
broadcasted messages to enhance the navigation 
accuracy and integrity of the core GNSS-1 elements 
GPS and GLONASS, and to exploit how the data 
can be used to compute and analyze the 
performance in terms of Required Navigation 
Performance (RNP) parameters. The paper describes 
the algorithm implemented to process the 
broadcasted EGNOS SIS in order to obtain a 
position solution and integrity information 
compliant with RTCA DO229C. Moreover, the 
paper presents test procedures and experimental 
results that may be used as a design guideline for 
monitoring manufacturing compliance and, in 
certain cases, for obtaining formal DO229C 
certification of equipment design and manufacture. 
On the other hand, concerning the development of 
new algorithms for Guidance, Navigation & Control 
of fixed wing vehicles, that are already compatible
with the future GNSS framework, it was initially 
considered a suite of navigation sensors with 
accuracy similar to the one obtainable by EGNOS. 
In order to overcome the effects due to an 
insufficient accuracy, the satellite measures can be 
in fact integrated with different sensor sources 
allowing a high precision navigation and an 
improvement of the integrity and reliability of 
navigation solutions. By means of an appropriate 
sensor suite, described in the next, and of a sensor 
fusion algorithm we obtained a high precision level
in navigation measurements that, for instance, 
allows a high autonomous precision approach and 
landing. A very simple but effective sensor fusion 
algorithm based on the use of complementary 
filtering technique has been implemented. 
Moreover, some critical autonomous functionality, 
such as Autolanding, will utilize the GPS integrity ignal in its decision-making logic for evaluating the 
key-decisions regarding the possible execution of an 
altitude recovery manoeuvre and, in case, also 
considering a degraded mode by changing the 
desired performances at touch down, with the aim to
be still compatible with the current navigation 
system precision. In this way the integrity 
information provided by EGNOS is efficiently used 
for achieving a higher safety level during 
autonomous flight operations. 
The selected on-board software architecture is 
actually fully compliant to the use of EGNOS based 
GPS units, without requiring any upgrade and the 
proposed sensor fusion algorithms have been 
already developed being basically compatible with 
integrity information coming from the future GNSS 
sensors. Anyway, in the presented first phase of 
flight experiments, we used a coarse DGPS unit, 
because EGNOS is still in the testing phase. The 
next steps are to perform autonomous GN&C flight 
experiment with EGNOS constellation with a 
runway completely not instrumented. 
In the first part of the paper, concerning EGNOS 
system characterization, is presented an overview of 
EGNOS (chapter 2), are described the processing of 
the SBAS Signal-In-Space correction and integrity 
data and the related algorithm to estimate the 
integrity supplied by the system (chapter 3), the 
classes of equipment at which the test requirement 
are referred and the equipment performance and test
procedure focusing on processing requirements and 
the validation performance assessment logic to 
assess the performance achievable with EGNOS 
(chapter 4). In its second part, describing the 
development of GNC algorithms already compatible 
with the future GNSS framework, the paper deals 
with the autolanding algorithms (chapter 6), the 
sensor fusion algorithms to achieve the desired 
navigation precision and the methodologies 
developed in order to safely manage the possible 
presence of sensor failures (chapter 5), the 
preliminary results of the real time validation with 
hardware in the loop simulation (chapter 7) and, 
finally, the algorithm performances achieved during
the first experimental flights by using the CIRA 
experimental flying platform (chapter 8). 
 
JF - ENC GNSS 2009 PROCEEDINGS ER -