Safe landings contribute largely towards every successful aircraft flight. Electronic instrumentation systems provide lateral and vertical guidance relative to the center of the runway for landing. Electronic instrumentation systems which aid in landing are generally Landing System Receivers. So, a landing system receiver’s capability should be validated for different approaches and landing paths. In this paper, we will discuss mainly how to generate different simulated flight paths to check the lateral and vertical guidance functionalities provided by the navigation receivers for FLS (Flight Management System (FMS) Based Landing System)mode.

1. Trajectory Generation for FLS Functionality Validation
Priyasloka Arya, Tarali Bora & Madhava Gadicherla
Abstract
Safe landings contribute largely towards every successful aircraft flight. Electronic
instrumentation systems provide lateral and vertical guidance relative to the center of the
runway for landing. Electronic instrumentation systems which aid in landing are generally
Landing System Receivers. So, a landing system receiver’s capability should be validated for
different approaches and landing paths. In this paper we will discuss mainly how to generate
different simulated flight paths to check the lateral and vertical guidance functionalities provided
by the navigation receivers for FLS (Flight Management System (FMS) Based Landing System)
mode.
Introduction
There are various phases of flight of an aircraft, namely Preflight, Takeoff, Departure,
En-route, Descent, Approach and Landing. Approach and Landing are the most critical phases of
flight. Various landing systems are in use currently e.g. ILS (Instrument Landing System), GLS
(GNSS (global navigation satellite systems) based Landing System), MLS (Microwave Landing
System), VOR/DME (VHF Omni directional Range/Distance Measuring Equipment), VOR,
NDB(Non directional Beacon), and RNAV(Area Navigation).These landing systems can be
broadly classified depending on the type of guidance they provide. The possible approaches
available are precision approaches, which provide both lateral and vertical guidance (e.g. ILS,
MLS and GLS) and non-precision approaches, which provide only lateral guidance (e.g. GPS,
VOR/DME, VOR, NDB and RNAV).
Figure (1): Various Phases of Flight
A non precision approach has guidance only in horizontal direction whereas as precision
approach has guidance in both horizontal and vertical direction.

2. FLS Approach
Different landing systems use different methods to compute the vertical and lateral
guidance. Conventional landing systems like ILS and MLS depend on RF signals from the
ground, GLS uses GPS/GLONASS signals and pseudo range corrections from ground-based
systems, Optical landing systems use Fresnel lenses and Image-based landing systems
incorporate image sensors to generate the image of the runway and then correlate predicted
coordinates and the detected edge of the runway image to compute the guidance.
A new approach to landing – FLS - is proposed by Airbus to augment the landing system
capabilities. FLS is considered as a non-precision approach because it derives deviation
information from non-precision sources like INS, GPS, DME and ADF. But, FLS still provides
lateral and vertical deviation similar to a precision approach landing system.
While the other landing systems use some “physical” form of a representation of the
runway centerline (RF- or optical-based), FLS and GLS use a “synthetic” representation of the
same. They calculate lateral and vertical guidance using mathematical models and proprietary
algorithms. The accuracy of the computed guidance depends on the computational efficiency
and effectiveness of the algorithm.
In this paper we will talk about how to generate a descent path and landing scenario to
verify the FLS landing system capabilities and the FLS algorithm functionalities.
Glossary of FLS terms
• The Anchor Point is a reference point defined on the Approach path. FMS
calculates/defines this point for a particular runway.
• The Runway Threshold is defined as the touch down point of the a/c on the runway.
• The Runway Threshold Altitude is defined by the following formula:
Runway Threshold Altitude = AP Altitude –H0
Where, H0= a predefined height (usually 50 ft.)
• Local Vertical for the approach path is defined as a plane normal to the WGS-84 ellipsoid
at the Runway Threshold (RT).
• The Local Ground Plane for the approach is defined as a plane perpendicular to the local
vertical and passing through the Runway Threshold.
• The Vertical Plane is defined as a plane containing the projected point of AP on ground
and the AP and the line which is in direction of the FLS Beam Course.
• The final Approach Path is defined as a line in the vertical plane passing through the AP
with an inclination (defined by the Slope) relative to the local ground plane.
• The Approach Angle (AA) is defined as the absolute value of the Slope or inclination.
• The FLS Beam Course is obtained by the following formula:
FLS Beam Course =Local Magnetic Variation + Magnetic Course of the Runway

3. Figure (2): A Typical Descent Path
Figure (3): Virtual Beam Formation
RT
AP
A/C
AP1
H
PAP
β G
AA
α
O

4. The aircraft (a/c) tries to maintain its descent along the approach path (RT-AP line). This
approach line makes an angle (equal to approach angle) with local ground plane. The A/C-RT
line makes a deviation angle β with the RT-AP line. H is the projection of the a/c position on the
ground level plane at RT, along a line parallel to the normal at RT. The line HO subtends an
angle α with the runway line.
A virtual FLS beam is defined as a line passing through the anchor point and making an
angle to the horizontal plane at RT equal to the angle of approach. In the FLS mode, the landing
receiver receives the anchor point ident, anchor point latitude, longitude and altitude, the latitude,
longitude and altitude of the runway threshold, the slope of the FLS beam, the local magnetic
variation, and the magnetic course of the FLS beam, latitude, longitude and altitude of the
aircraft from the FMS system via Arinc-429 port. Thereafter the landing receiver calculates
lateral DDM (Difference in Depth of Modulation) and vertical DDM using this set of inputs. The
lateral and vertical DDMs are directly proportional to lateral deviation angle α and vertical
deviation angle β (see figure (2) above).
Flight Configuration of MMR
INPUTS OUTPUTS
Figure (4): An On Flight MMR configuration
The MMR O/Ps the lateral and vertical DDM on the ILS look-alike Arinc-429 buses,
where one is connected to the EFIS (Electronic Flight Instrument System) and other is connected
to the FMS (Autopilot).
* Anchor point indent
* Anchor point lat, long and alt
* Lat and long of runway threshold
* Slope of the FLS beam
* Local magnetic variation
* Magnetic course of the FLS beam
* Aircraft Lat, long and alt
* Aircraft Lat, long (fine)
MMR
* Lateral and Vertical dev
* Distance to Anchor Point
*Aircraft Lat, long and alt
* Distance to Anchor Point
L DDM
EFIS
INS
GNSS(GPS)
FMS
Autopilot
VOR
DME
V DDM

5. Simulation of Landing Phase In a Test Bench:
For the validation of the FLS function, we need to use multiple sets of input parameters
like aircraft latitude, longitude and altitude. The remaining parameters, which are specific to the
airport and runway, are considered to be constant. To simulate the landing phase, we need to
provide latitude, longitude and altitude for different positions along the descent path. Depending
on the aircraft position and runway selection, the MMR outputs DDM and the status of the DDM
(i.e. SSM (Sign/Status Matrix) is set to NO (Normal operation) or NCD (No computed Data)). If
the distance between the aircraft position and anchor point is within some predefined limit, DDM
status show NO, otherwise it indicates NCD.
A typical Test Bench set up
INPUTS OUTPUTS
Test Report
Figure (5): Test Bench configuration of MMR
TEST
BENCH
* Anchor point indent
* Anchor point lat, long and alt
* Lat and long of runway threshold
* Slope of the FLS beam
* Local magnetic variation
* Magnetic course of the FLS beam
MMR* Aircraft Lat, long and alt
* Lateral and Vertical Deviation
* Distance to Anchor Point
* Aircraft Lat, long and alt
* Distance to Anchor Point
* Aircraft Lat, long (fine)
Pass/Fail Criteria

6. There can be different methods to generate test points along the chosen descent path. One
such approach is where we consider a set of discrete points along the path.
An approach path can be chosen which is above/below and/or to the right/left of the ideal
approach path. The distance from the anchor point and the required lateral and vertical DDM are
inputs. From the lateral DDM the lateral deviation angle can be computed. Using standard
navigation algorithms e.g., Sodano or Vincenty direct equations the latitude and longitude can be
computed; and given the vertical DDM, the altitude of the a/c can be computed. Similarly other
points can be chosen along the path. These points can also be fed to the MMR during testing and
DDM outputs from the MMR can be compared to the expected theoretical DDMs as computed
above. The pros and cons of this kind of approach are given below.
Pros:
• We can generate different discrete points by a piece of software program.
Cons:
• The discrete points generated could be unrealistic considering aircraft dynamics, i.e., it
may be impossible for the aircraft to move from one test point to the next test point with
given speed and acceleration.
Another approach is to use a third party tool like Spirent SimGEN© which simulates the GPS
signals, corrections and aircraft dynamics like acceleration, turn, climb and speed. It has the
provision for defining different way points on the flight path. A trajectory can be generated by
connecting all the waypoints. A typical motion or aircraft command file looks like:
Figure (6): A Snapshot of an Aircraft Motion file

7. Figure (7): A Simulated Trajectory in SimGen
Pros:
• By providing the discrete waypoints, a trajectory can be generated connecting all the
given points.
Cons:
• It is a very good way for simulating all possible paths of all phases except landing phase
where we have to again calculate discrete points. The discrete points may be unrealistic
as proper dynamics of the aircraft during landing should be known before hand.

8. Proposed Way of Trajectory Generation
So a different methodology is proposed for a realistic path generation for landing phase.
Microsoft Flight Simulator© (FS) 2004 is chosen for flight model selection (Boeing/Airbus),
airport selection, flight parameter selection (engine command, autopilot command, radio
command, Instrument command, and view command).Using this Simulator an appropriate path
can be generated .The details of this scheme are given below.
(Flight Simulator)
(FSUIPC)
Test Report
Flight Parameter
Extraction Program
TEST
BENCH
(FLS ALGO
IMPLEMENTED)
MMR
Trajectory File
Visualization Tool
(With FLS Algo implemented)
Joystick
Approach
Volume
Pass/Fail Criteria
--- Dotted Line shows proposed plan
Figure (8): Schematics of Proposed Plan

9. Flight Simulator provides ample scope for generating a test flight path. It lets the user
choose an aircraft model from a pool of available models, the flight plan can be prepared
depending on the source and destination airport and different navigation schemes can be chosen
e.g., GPS and VOR. The aircraft can be controlled by a joystick and a flight path is generated.
A data extraction program is written to extract data (latitude, longitude, altitude, heading,
roll, pitch, yaw etc.) from Flight Simulator’s common memory and provide it to another
visualization tool in near-real time. This proposed tool is developed in VC++ IDE with OpenGL
API. Using this visualization tool, the user can visualize the aircraft and its path in three
dimensions with source, destination airports and the approach volume (see Figure (8)) for the
landing. Viewing the flight path in three dimensions using the visualization tool, the engineer can
fly the path in Microsoft Flight Simulator to generate a test path along waypoints that have been
predefined in the visualization tool, thus generating a more realistic flight path.
This novel approach is suggested for realistic flight path generation for testing of the FLS
function. The generated trajectory file consisting of aircraft latitude, longitude and altitude can
be provided as an input to the MMR. The DDMs computed by the MMR are then fed to the test
bench for comparison with theoretically generated values and generation of a pass/fail report
Here, it must be ensured that the FLS algorithm implemented in the Test Bench should be
the same as the algorithm implemented in MMR.
The salient features of the proposed methodology are furnished below.
• The aircraft dynamics are taken care of in Microsoft Flight Simulator (FS).
• FS has a huge database of airports and their facilities related to communication and
navigation at ATC (Air Traffic Control).
• FS has various a/c models. So, a particular aircraft type can be selected for flight.
• FS gives graphic instrument panel to control different instruments, various indicators
(e.g. Airspeed, Altimeter, Heading etc) for display and radios (e.g. VOR, DME, ILS etc)
for navigation.
• Flight trajectories can be generated by using joystick controls.
• The visualization tool helps as a manual feedback so that we can restrict the aircraft in the
approach volume.
• The actual position of the aircraft and its relative position to the destination airport can be
easily comprehended by using the visualization model.

10. In this proposed implementation there are some limitations which are to be addressed.
• Flying an aircraft in FS using the visual model needs a minimum required skill.
• The data update from the flight simulator is around 1 sec.
Conclusion and Scope:
These above issues are not serious constraints for the proposed implementation. With a
little dedicated effort, a good flight path can be generated in Flight Simulator. Also, solutions
could be worked out to increase the data update rate, but the1 sec update rate is deemed to be
sufficient for testing.
The deviation data (DDMs) can be compared with respect to other legacy landing system like
ILS for accuracy verification of FLS algorithm.
Acknowledgement:
The authors express their deep gratitude towards their colleagues Ashish, Naina
Anupama and Nagmani for proof reading the manuscript and giving their feedbacks. We are
grateful to Mr.George Koilpillai for his encouragement while carrying out this work. Special
thanks for Rajnikant for resolving proprietary issue and his support and motivation.
References:
1. Avionics Navigation Systems, Myron Kayton and Walter, A Wiley-International
Publication
2. Windows Sockets Network Programming by B. Quinn & D. Shute, Addison-Wesley
Publishing Company
3. Arinc-755-3(Multi Mode Receiver (Digital)
4. Redbook(The official guide to learn OpenGL) Version 1.1
5. VC++,COM and Beyond, Yeshvant P Kanetkar,Sudesh Saoji,BPB Publication
6. FSUIPC Documentation
7. United States-Patent Application Publication Pub. No.: US2004/0199304A1
AIRCRAFT PILOTING SYSTEM, AT LEAST FOL PILOTING THE AIRCRAFT
DURING A NON PRECISION APPROACH WITH A VIEW TO A LANDING
Inventors: Gilles Tatham, La Salvetat, Saint Gilles (FR), Eric Peyrucain, Saint
Genies, Bellevue