Alexander Kwartiroff

Technology Team Leader, Avionics

Parker Hannifin Electronic Systems Division (ESD)

300 Marcus Blvd.

Smithtown, N.Y. 11787

United States

**REAL-TIME DATA TRANSMISSION FROM AIRCRAFT**

##### ABSTRACT

While performing a flight inspection mission, the results of the
facility performance are presented to the operator in various types of
displays, such as a colour monitor, and printer/plotter. The data may
also be digitally recorded for subsequent analysis on the ground.
However, no facility performance information, other than a pass/fail
decision, is available until the aircraft completes its mission and
returns to its home base.

In certain types of inspections, such as periodic with monitors and
commissioning for ILS and MLS, it is useful for the personnel on the
ground to receive real-time data that is observed in the aircraft. This
paper will discuss the types of data displays presented on the ground
that contain facility performance information in real-time as it is
monitored in the aircraft. Furthermore, the architecture of the airborne
equipment to support this capability will be addressed.

In the future, the Parker Automatic Flight Inspection System (AFIS)
architecture will be able to support remote control of the flight
inspection equipment, using a high-speed data link interface when it
becomes cost effective. This capability already exists today having
successfully controlled and monitored the flight inspection equipment
remotely via an Internet connection. Using this approach, the operators
could be placed in a centralized location on the ground, instead of the
aircraft, thus reducing the cost of flight inspection operation.

##### INTRODUCTION

Over many years the flight inspection equipment has been upgraded to
provide enhanced system performance by gradually phasing in new
capabilities. This was necessary to satisfy the changing requirements
for flight inspection imposed by new navaids and procedures, as well as
to use new technology for improving the way the flight inspection
mission is accomplished. One of the areas where much emphasis has been
recently placed is reducing the overall cost of carrying out the flight
inspection mission.

The approach that has been successfully used by Parker is one of
technology insertion. Instead of replacing the entire flight inspection
equipment, it has been upgraded in a phased implementation using
state-of-the-art technology to provide enhanced system capabilities. One
of the latest technology upgrade is the introduction of the Ethernet
data link, interfacing the major flight inspection subsystems in the
aircraft. This architecture allows a radical change in the way flight
inspection is implemented. Eventually, one can visualize an environment
where the flight inspector will no longer be monitoring and controlling
the equipment from within the aircraft. Instead, this function could be
performed from a centralized location on the ground interfacing to all
flight inspection aircraft over a high-speed satellite wide area data
network.

This paper presents how this technology evolution is being applied to
achieve this ultimate goal.

##### ORIGINAL SYSTEM ARCHITECTURE

The Parker AFIS architecture has been evolving for over 15 years.
Therefore, design decisions were made based on the best available
technology at that time. In those days display technology was limited to
only dumb terminals, and consequently, the screen data formatting
function has been allocated to the Navigation Computer Unit (NCU).
Figure 1 illustrates the top-level interfaces between the major system
components in the original design.

The RS-232 interface between the NCU and In-Flight Workstation (IFWS)
was adequate to transmit the screen display information from the NCU,
and to send the control commands from the IFWS. Subsequently, a digital
data logger was added through a SCSI interface connected

to the NCU. SCSI supported data logging adequately, however, being a bus
interface primarily limited to peripheral devices, it could not have
been easily expanded to communicate with additional devices. Even though
this architecture fulfilled the flight inspection needs, it had
limitations for future growth and expansion.

![](media/image1.wmf)

##### ENHANCED SYSTEM ARCHITECTURE

The introduction of Ethernet is part of an on-going strategic
enhancement that Parker has undertaken in the last few years. The
results of this activity has significantly impacted the architecture by
changing the functional partitioning of the major sub-systems within the
aircraft environment, and by opening new opportunities in the ability to
transmit processed facility parameters to the ground personnel in
real-time. Specifically, Ethernet established a high bandwidth
communications link from the NCU to the IFWS, which has re-allocated a
part of the real-time processing to the IFWS. The IFWS, now being a
smart terminal, is capable of data processing and interfacing to other
peripheral devices. Figure 2 depicts the changes to the interfaces made
in the enhanced system architecture.

The first implementation of Ethernet has been interfacing the Television
Positioning System (TVPS) controller to the IFWS. All of the controls
and processing of the threshold image cursor positioning are now handled
within the IFWS, and after making

![](media/image2.wmf)

the computation for the final fix correction, it is transmitted to the
NCU.

The benefits resulting from this modification are quite extensive. The
IFWS has access to the entire set of the real-time data generated by the
NCU. The IFWS can process this data, and generate real-time graphical
displays using off-the-shelf Windows application programs. Virtual
plotting of pop-up displays is easily implemented as well.

The next enhancement utilizing Ethernet connectivity between the NCU and
the IFWS is the Remote File System (RFS) which was developed on the IFWS
to save disk logger files. Basically the RFS and supporting NCU software
is similar in concept to a network file server. The RFS responds to NCU
file operations such as open a file, read and write data, and close the
file. This architecture allows log data to be shared and accessed by
various IFWS based applications. In the previous NCU architecture, data
logger files were written to a SCSI disk drive controlled by the NCU. In
order to share data, the operator had to eject the hard disk media and
remount it into another disk drive on the IFWS. In the new design, the
flight inspector can readily access logged data throughout the flight
inspection mission, and has the capability of preparing reports on
completed facilities while flying to the next inspection site.

The incorporation of an Ethernet backbone into the AFIS provides a
simpler approach of integrating other peripheral devices to accommodate
future growth.

##### DATA CONVERSION AND TRANSMISSION TO GROUND

The next enhancement to the Parker system was the development of the
Logger File Conversion Utility (LFCU). This Windows based program
provides the user with the ability to selectively extract inspection
logger file data fields. The LFCU works in both an interactive and
automated mode.

In the interactive mode, the user selects data fields from a selection
screen shown in Figure 3. The data selection criteria can

be saved and later recalled. Each AFIS log file format is defined in
external definition ![](media/image3.png)Figure 3. Data Field Selection.

tables. These tables specify data field

![](media/image3.bmp)names, data types, location in the record, and the
default conversion units. The external tables provide flexibility for
modification and version control. Various data conversions are also
performed on the data fields. For example, distances can be converted to
nautical miles, feet or meters.

Figure 4. Data Extraction Block Diagram.

In the automated mode, previously defined selection criteria is
automatically applied to a log file. When the user starts the extraction
process, the requested data

fields are extracted from the log file and written to a new output file.
The output

file is created in a format so it can be used as input to other user
applications such as

Microsoft Excel.

A third enhancement dynamically links the RFS and the LFCU. This feature
provides

a direct link into the LFCU data extraction

process as the data is being written to the

RFS by the NCU in real-time, as shown in the block diagram in Figure 4.
A special output format compresses the data so it can be transmitted to
the ground using a 2400 baud rate VHF radio data link. Even though this
is a limitation in the amount of data that can be transmitted, useful
information can be collected by ground personnel performing site
evaluation analysis.

As an example, for an ILS inspection data is collected and processed in
the airborne flight inspection equipment eight times a second. The
instantaneous data consists of RNAV parameters (A/C position, velocity,
heading, altitude) and facility data (modulation, signal strength,
deviation, etc.). The final processed data computed after the completion
of each run provides facility performance parameters, such as alignment,
symmetry, and structure. Even though all instantaneous data cannot be
transmitted in real-time at the 2400 baud rate, selected parameters can
be sent using a data compression algorithm. The filtering of the
transmitted parameters is accomplished using the data selection screen
shown in Figure 3. On the ground, this data is expanded and used as
input to a graphical display program.

The architecture shown in Figure 4 is not limited to local data
transmission using low data rates. This design can easily accommodate
other types of transmitters or wireless links. In the future, when the
cost of high speed satellite data links becomes affordable, the aircraft
flight inspection system can be connected to a wireless Ethernet wide
area network, as portrayed in Figure 5.

![](media/image4.wmf)In this environment, real-time flight inspection
data could be transmitted to a ground based central data base where all
facility records are maintained, and the required processing is
performed to determine the operational status of each navaid. Reported
failures or discrepancies would be disseminated in a timely fashion to
the designated authorities.

##### DATA PROCESSING AT FACILITY

So far what was discussed in this paper is the airborne flight
inspection equipment architecture enhancements, supporting the
extraction and processing of facility parameters for transmission to the
ground. What are the benefits and advantages to receive real-time data
at a facility from the aircraft that is performing its inspection
mission? First, we will address the application of such data at an ILS
facility undergoing site evaluation or commissioning. And finally, a
future methodology to control the airborne Flight Inspection system from
a remote ground location will be presented.

##### 

As part of the site evaluation for a new navaid installation, the
downlinking of data from a flight inspection aircraft is necessary to
make the decision process more timely. The information is used to:

1.  Make adjustments to bring facilities to an in-tolerance condition,
    or to optimize performance.

2.  Determine if a site being tested is suitable for a permanent
    installation.

3.  Decide on the type of antenna system to install after a site test.

4.  Evaluate problems to decide the course of action, i.e. remove a
    hangar or modify/relocate an antenna system.

5.  Decide on whether to modify antenna systems if the facility
    performance is less than desirable.

Evaluation of real-time data may reduce the time spent flying a facility
if it points to multipath as the source of a problem, instead of other
easily fixable conditions, such as transmitter adjustments. Also,
real-time data can be used to best utilize the runs, so that the
altitudes (or other flight maneuver choices) that are used demonstrate
the problem most clearly.

**Multipath interference** is a concern for many types of ground-based
navaids: localizer (LOC), glide slope (GS), and very high-frequency
omni-range (VOR) facilities are especially vulnerable to it. This is due
to these systems radiating multiple signals, including some that do not
contain carrier energy. One \"classic\" example of LOC multipath is
shown in Figure 6. In this example, the energy that travels directly
from the LOC to the receiver is called the direct energy. Energy will
also arrive at the receiver by way of the hanger and this is called the
reflected energy ("multipath"). The "angle of incidence" (δ on the right
side of the hanger) will be equal to the "angle of reflection" (δ on the
left side of the hanger) of the multipath signal. Due to fact that these
two angles must be the same, there is a specific area in which multipath
is expected to have an effect. This area of potential interference is
shown in Figure 7.

For the \"classic\" multipath case shown in Figure 6, the aircraft
receiver output (the crosspointer trace on flight inspection records)
will oscillate or produce scallops as a result of the algebraic
summation of the signals. The length of the scallops is a result of the
geometry, and the amplitude of the scallops is a result of the
reflection coefficient of the reflector.

![](media/image5.wmf)The navaid receiver output will be a complete
sinusoidal scallop (360 electrical degrees) every time the difference in
the path lengths changes by 1 wavelength (at the operating frequency of
the system). For the LOC shown in Figure 6, this means that when the
difference between the incident plus reflected path length and the
direct path length changes by about 8.9 feet (a localizer wavelength) a
complete scallop is produced. The actual value of \[(incident +
reflected) -- direct\] is not important, it can be several hundred feet;
what is important is that the receiver output will be a complete scallop
each time the difference in the expression \[(incident + reflected) --
direct\] changes by 1 wavelength. The distance an aircraft flies for
each complete scallop at the receiver output is determined by the
relative geometry of the navaid, the reflector and the receiver.

As far as the real-time data being used to evaluate multipath, the
crosspointer, the modulation traces, and the AGC are primarily looked
at.

![](media/image7.wmf)One of the uses of real-time data is to optimize
facilities in which the multipath aspects may be noticed, but not
evaluated in detail. An example is to adjust the antenna phasing of a
glide slope and be able to readily see its effect on the signals
measured by the aircraft. By having the ability to view real-time data,
many of the nuances of improper phasing adjustments may be easily seen
on the received signals, and the proper adjustments can be made. This
information is not completely described by the data announced by the
AFIS computer. However, such numbers can be easily communicated to the
ground using a radio data link, and this has been the only method of
sharing data with the ground other than landing.

As far as displaying the information, it is desirable to view a
graphical display of the traces, something like the graphical traces of
a flight inspection record. The scalloping levels provide very valuable
inputs in determining the facility operational performance. As far as
the computer announcements, such as path width, alignment, etc. they are
useful as well.

The system used on the ground for this type of work has an alpha-numeric
screen for controlling the saving of data and starting/stopping a run.
After the completion of a run, a Windows-based graphical screen provides
the ability to look at a portion of the data that is of interest. An
additional feature is available that can display the alpha-numeric
information for a given frame of data so that digital precision is
available, if desired.

Figure 8 is representative of a graphical display of a Localizer ILS-3
run that was generated from actual data received from the aircraft. The
top (black) line is the raw crosspointer data, the second line from the
top (blue) is the theodolite, the third line from the top (red) is the
corrected trace, and the bottom line (red-brown) represents the marker
beacon traces. The 250 line represents ideal alignment for the red
corrected trace. The outer marker is shown on the left side of the
screen, and the middle marker is shown on the right. The scale at the
bottom is (from top to bottom): time stamp, distance from localizer in
NM, azimuth from runway centerline and vertical angle from localizer.

##### REMOTE CONTROL FROM GROUND

One application that has not yet been discussed is the future
possibility of controlling the airborne flight inspection equipment for
the entire aircraft fleet from a centralized location on the ground.
This new approach could offer substantial financial benefits to an
organization like the FAA, operating a large fleet of aircraft.

In this environment, the flight inspector would no longer be located in
the aircraft, but instead would be operating from a central ground
location, having access to the flight inspection system in all the
aircraft. In effect, the display and control capabilities would be
identical as if he was flying in the aircraft. Furthermore, since all
facility parameters would be immediately available on the ground,
experts, possibly from a remote location, could address performance
issues in near real-time prior to the aircraft leaving the area.
Facility malfunctions would be resolved in a much more expeditious and
economical manner. This technique is realistic based on records
indicating that approximately 85% of inspections are routine in nature,
requiring little operator intervention. However, to maintain local
control capability, the IFWS will remain in the aircraft.

Another benefit to this approach is the essential elimination of all
travel requirements for flight inspectors. The ground-based location
selected for the operation and control could be centralized, or
distributed among several offices throughout the country.

And finally, another potential advantage is the efficiency of
implementing the entire flight inspection mission. In today's
environment much of the time is spent flying from one facility to the
next, where no flight inspection activity is taking place. Therefore, by
having a staff of inspectors in a central location, one individual could
control and monitor more than one aircraft at a time. But even if this
efficiency cannot be achieved, the inspector would be more productive in
a comfortable environment on the ground, and could work on the
preparation of inspection reports while the aircraft is re-positioning
from one facility to the next.

In summary, a productivity improvement can be realized with a
ground-based centralized operation and control of the airborne flight
inspection equipment. Even though this feature can be implemented using
technology that is available today, the decision is based on the cost
trade-off of accessing a high-speed data link system. It is recognized
that even though at this time this is not a cost-effective solution,
data transmission costs have been going down, and this alternative may
be practical in the not too distant future.

##### REMOTE CONNECTIVITY USING INTERNET

##### 

To validate the concept of remote connectivity of a flight inspection
system, Parker and the FAA conducted a test in late 2001. The purpose of
the test was to determine if a flight inspection system could be
reliably operated from a remote location.

The test consisted of controlling and monitoring the flight inspection
equipment, located in the Parker laboratory in Smithtown, New York, from
the FAA site at the Mike Monroney Aeronautical Center in Oklahoma City.
The IFWS at the FAA was connected to the NCU at Parker through the
Internet using the Ethernet TCP/IP protocol. Figure 9 is a diagram of
the equipment and its interfaces used to perform this test.

It was important to run the system under realistic operational
conditions to identify effects from potential message propagation
delays. The NCU was operating with a dynamic Simulator that simulated
all aircraft RNAV and inspection receiver signals. The ILS-3 Mode was
selected on the Simulator and the control to initiate the run was
![](media/image8.wmf)executed on the IFWS at the FAA. Coordination of
activities was accomplished by telephone.

From the beginning of the run which was initiated at the FAA, the
operators commented that the "touch and feel" of the system was
identical to a normal local operation. Both execution of commands and
display of the flight inspection data on the monitor did not show any
noticeable delays. In summary, the FAA personnel felt that the operation
of the system from a remote location was a success, and this technique
opened the door to a possibly different implementation policy for the
flight inspection mission.

##### CONCLUSION

The Parker flight inspection system has been in operation for over 15
years. During this period many enhancements have been implemented to
satisfy the continuously changing requirements for inspecting new types
of facilities, and the use of GPS in the approach procedures. Recently,
advances made in the field of communication technology have allowed the
development of new capabilities that may have a financial benefit in the
operation of the flight inspection mission.

In particular, real-time data transmission from the aircraft provides an
opportunity to modify some of the methodology in the performance of
flight inspection. One such aspect is to provide personnel, located at a
facility, parameter information as observed in the aircraft. This has
been demonstrated to reduce the time it takes to make adjustments to the
various facility components.

And recently, a significant breakthrough was achieved by operating the
flight inspection system from a remote location over the Internet. As
the cost of high-speed communication decreases, remote control from the
ground may be a cost-effective solution in the not too distant future.

##### REFERENCES

Engineering Notes,

FAA, Fort Worth NAS Implementation Center, Navigation/Landing Platform,
ANI-680.

"Effects of Multipath on Navaid Facilities",

Revised January 16, 2001.