1. INTEGRATION OF UNMANNED AIRCRAFT SYSTEMS
INTO THE NATIONAL AIRSPACE SYSTEM
Author: Wilson J. Ragle
Class: AS 403 Section 1
Professor: Tom Haritos

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1. Introduction
The National Airspace System (NAS) has been becoming busier ever since the
Wright Brothers first took off and the first air mail routes were created in the early 1900s.
During this day in age the NAS supports nearly 87,000 flights per day and is immensely
growing as the need for transportation of goods, people, and services are constantly in
demand and even growing in demand. With the introduction of Unmanned Aircraft
Systems (UAS) into the NAS, the airspace is getting even more congested due to the lack
of set in stone regulations from the Federal Aviation Administration (FAA). Now that
UAS are becoming more common amongst the general population, the airways are
become much less predictable and much less safe, which causes a threat to the manned
general aviation community. Many of the manned aircraft in the sky are non-
cooperative, meaning the pilot has no way of complying with air traffic control directions
or contains the equipment needed to see other aircraft in the sky around it. This brings us
to the problem of Detect and Avoid (DAA), which is the portion of the FAA regulations
that this research paper will discuss. DAA capabilities can be completed using many
different types of sensors such as LiDAR, RADAR, SONAR, Active and Passive
Microwave, and many more. While many of these different sensors have the capability
to DAA other aircraft, we must determine which of these is the most reasonable and
effective way of accomplishing the task.
2. Problem
With the number of UAS in the air today at an all-time high, so are the
possibilities of collision between manned and unmanned aircraft. The FAA has told us,

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the American people, that UASs must be able to maintain separation both in visual and
instrument conditions as well as in lost link situations. However, these technologies
needed to complete the task of maintaining separation and staying well clear of other
aircraft in the sky require sensors and systems that are not small enough, light enough, or
can receive enough power from the smaller systems. These small UAS are the most
common in the United States due to how cheap and easy it is to get a hold of the
equipment. Although UAS are becoming more and more common, the FAA has decided
that the initial regulations will be targeted towards UAS that are between Group 3 and
Group 5 according to the Department of Defense UAS categorization table. The focus on
UAS over 55 lbs is because of their greater ability to comply with the regulations that
will be set forth by the FAA. Because of the ability for all unmanned aircraft to be able
to detect and avoid, a uniform set of sensors and systems needs to be created to ensure
that all UASs are compatible not only with each other but also with the cooperative and
non-cooperative aircraft.
3. Projected Solution
Detect and Avoid is the main problem when looking at the relationship between
unmanned aircraft and manned aircraft flying in the sky together in this day in age.
There is really no uniform way to automatically DAA manned aircraft in the NAS today,
which is exactly what the FAA is trying to change. There needs to be a set of sensors and
systems that will allow these UAS to DAA both when there is signal and a loss of signal.
The projected solution is a combination of a Traffic Alert and Collision
Avoidance System (TCAS), Automatic Dependent Surveillance- Broadcast (ADS-B),

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Radar, and Electro-Optical/Infrared (EO/IR) systems. The reason behind having TCAS
and ADS-B is to be able to DAA the cooperative aircraft, while the SAR and Laser
systems are for the DAA of non-cooperative aircraft which is talked about extensively in
the DSA Literature Review. A visual representation of the traffic will be shown in a
virtual reality head set to provide another layer of awareness that will be secondary to all
of the other information coming in.
4. FAA Regulations
The FAA Directive 7610.4J and FAA UAS Roadmap also states that the safety
requirements need to be comparable to the DAA for manned aircraft. Thus, we must
follow Part 91, 91.111, 91.113(b), and 91.181(b) under Title 14 Code of Federal
Regulations which are the regulations on who has the right of way and staying clear of
other aircraft. The interpretation of these regulations however are not very clear and can
sometime be considered very vague. The gist of these regulations is that the pilot in
command must be able to maintain separation between aircraft, which is very vague
because of lack of distance requirement information. The pilot could very well make the
argument that separation is just enough that the two aircraft do not hit.
5. Automatic Dependent Surveillance- Broadcast (ADS-B)
ADS-B is a relatively new technology that is used to allow the pilots to see the
other aircraft in the airspace ahead of them. Position, altitude, speed, flight number, type
of aircraft, if the plane is turning, climbing, or descending are all information that ADS-B
is capable of providing according to the FAA. This information is very valuable to the

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DAA of aircraft because it allows the UAS to determine the flight path of the aircraft in
front of it and find the best way to avoid conflict. According to Garmin and the FAA, the
effective range of the ADS-B is close to 150 miles which is plenty distance to DAA other
aircraft especially given the information that is recovered. This is a great way to ensure
that the conflict is resolved in sufficient time and is never a major risk to the lives of the
people aboard the manned aircraft.
Although there are many advantages to having the ADS-B system, there are also
some disadvantages to having the system. One of the biggest disadvantages that ICAO
states in their report is that the only source for pinpointing the aircraft location is GPS,
which is not a good way to ensure that the position is accurate. It is also not good
because the system does not have any back up way to find the position. Stated in the
International Journal of Aerospace Engineering, a big disadvantage is that because of the
need to use GPS with ADS-B, the possibility of jamming that could ruin the DAA
capability between cooperative aircraft. While this is a disadvantage, the FAA should be
able to reduce the likelihood of inaccurate positions by enforcing regulation that could be
put forth. Another way to compensate for the loss of GPS is that the ADS-B Radar patent
describes how it can modify the system by adding a radar processor thus making the
ADS-B also act as a primary radar system for detecting non-cooperative aircraft.
In the journal article titled “Realities and Challenges of NextGen Air Traffic
Management: The Case of ADS-B” by Strohmeier, Schafer, Lenders, and Martinovic
(2014), the case for ADS-B is made. In the article, the point is made that most of the
airlines have already started to put ADS-B equipment into their aircraft. That means that
ADS-B information is already being used across the world and is being studied as a

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possible way of detect and avoid operations. The article also said the following
statement, “Industry and regulator estimate that in 2013 more than 70 percent of all
commercial aircraft worldwide were already equipped with ADS-B transponders.
Countries such as Australia and Canada have already deployed full continental coverage,
with ADS-B sensors being the single means of ATC in low population areas of the
country.” While weather is an effect in some other systems, this article shows that
weather effects have been found to have very little effect on the system. Mentioned in
the article are reasons why ADS-B messages were not coming through as much as
expected. The article written by Strohmeier, Schafer, Lenders, and Martinovic (2014)
describe how there is a lot of clutter on the 1090 MHz frequency which is one of the
reasons for less message and another being that each aircraft has different modes of
transponders which could be a reason why the messages are slow to appear.
Since ADS-B is a new technology, not all planes have the technology in the
cockpit today. Thankfully, the FAA is requiring all aircraft that operate in airspace where
a Mode C transponder is required to use an ADS-B system starting on January 1, 2020.
Because of this, the airspace will become much safer for UAS and manned aircraft to fly
in together. Although this does not fix the issue of the other airspace where Mode C is
not required, it does fix the issue of being able to DAA in the Class A, Class B, and Class
C airspace.
6. Traffic Alert and Collision Avoidance System
Traffic Alert and Collision Avoidance System is a system that interrogates only
cooperative aircraft. Aircraft are considered to be cooperative when they have a means

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of communication with Air Traffic Control (ATC). Since TCAS can only be used
between aircraft with a transponder, that makes all of the aircraft cooperative.
The way TCAS works is that it sends out a secondary radar and transponder
signal to other aircraft’s transponder. The transponder then responds with information
such as closing speed, ascent and descent rate, as well as a suggestion as to how to
resolve the situation. The resolution could be calling for the pilot to climb, descend,
increase climb, or increase descent. The way a TCAS usually goes about the resolutions
is to advise one aircraft to climb and the other to descend which causes the issue to be
resolved quicker. All of these resolutions are to change the direction vectors of the
aircraft to make sure the two aircraft do not collide.
While TCAS is a great way to get information from a cooperative aircraft, is not
primary way of providing DAA capabilities to the aircraft. The best way to incorporate
TCAS into a UAS is to pair it with other sensors such as airborne radar, passive or active
radar, ADS-B, or possibly sonar. The combination of more than one sensor will allow
TCAS to provide information to the other information collected by the other sensors.
7. Electro-Optical/Infrared (EO/IR)
An Electro-Optical/Infrared system is used to determine an object against a
background that can sometimes make differentiating between the background and the
object difficult. The EO/IR system is a passive system, meaning that it relies on
moonlight, sunlight, and other energy sources from the environment to illuminate the
target. The system sends out streams or beams of photons which are how the UAV will
be able to sense the other aircraft in the sky. Since this is a passive system, it is also

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meant to be used in detecting non-cooperative aircraft. The Institute for Defense
Analyses writes that the photon beams are strong enough to travel through “hostile
mediums”, which would be parts of the atmosphere like clouds, rain, snow, and any other
types of precipitation or cover. Because of the ability to see through clouds, the UAS
will have greater awareness because of the ability to see through the medium and not
have to rely on visual observation of the aircraft.
Griffith, Kochenderfer, and Kuchar (2008) did a study using the Northrop
Grumman Global hawk UAS where they tested the ability of the three camera EO/IR
system to detect non-cooperative aircraft in the airspace. The main target of the study
was finding the size of the aircraft that can be detected by the EO/IR system. Griffith,
Kochenderfer, and Kuchar (2008) concluded that larger aircraft such as the Boeing 737
are more likely to be detected than small aircraft such as Cessna 172 size aircraft.
Griffith, Kochenderfer, and Kuchar (2008) also concluded that the likelihood of detecting
smaller aircraft can be affected by changing the field of view of the not only of aircraft
but also the horizontal stabilization of the EO/IR sensor.
Another study of and EO sensor by Lapierre, Borghgraef, and Vandewal (2010)
uses their system in order to detect sea vessels that could be in distress or have had to turn
off their Automatic Identification System which is required for vessels longer than 45
meters. The same ideas can be used for tracking of non-cooperative aircraft in the air.
Lapierre, Borghgraef, and Vandewal (2010) show that they are looking at disruption
patterns in the water in order to find the vessel even though it does not have and
Automatic Identification System. The same way that you can find vessels in the water is
also possible for finding aircraft in that you could probably look behind the aircraft to

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find disturbances in the air. This help to pinpoint the aircraft in the sky and be able do
the DAA procedures for the non-cooperative aircraft.
8. Radar
Radar is a system that will be uses for the aircraft in the airspace that are non-
cooperative. The reason for non-cooperative DAA systems is to ensure that those aircraft
that do not have ADS-B or TCAS can be sensed by the UAS and are still able to DAA as
well as maintain separation. The way radar works is that a transmitter sends a signal to
an antenna which in turn propagates that signal as a pulse which then interacts with the
environment. The pulse will then either scatter, reflect, or be absorbed into the objects
and the return signal will then be sent through the receiver and to the processor in order
to be displayed. The display of the radar information will then be able to tell distance to
the object. By simple creation of an algorithm, the processor will be able to sense the
closing rate by the change of distance between pulses.
Accardo, Fasano, Forlenza, Moccia, and Rispoli (2013) conducted a flight test
study of a DAA system that utilizes Ka-band radar combined with EO/IR sensors. The
Accardo, Fasano, Forlenza, Moccia, and Rispoli (2013) test was conducted on a very
light aircraft platform where all of the sensors were positioned on top of the wing.
Accardo, Fasano, Forlenza, Moccia, and Rispoli (2013) conducted two portions of the
flight test, one being the Chasing Phase and the other being the Quasi-Frontal Encounter
portion. The results of the Chasing Phase showed that when the aircraft was following
and “intruder”, the system was able to maintain the distance between the two aircraft
which satisfies the separation problem. For the Quasi-Frontal portion of the test, there

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was a greater level of error because of the field that the sensor is detecting at all times.
Accardo, Fasano, Forlenza, Moccia, and Rispoli (2013) found that some ground-based
targets would get mixed in with the intruder aircraft. While this is a problem with having
the error, the error is very minor which makes adjusting for the error easier.
Barott, Coyle, Dabrowski, Hockley, and Stansbury (2014) have gone into detail of
how the radar and EO/IR sensors will work together in order to determine the class of the
aircraft being remotely sensed. Barott, Coyle, Dabrowski, Hockley, and Stansbury
(2014) have come up with 3 separate steps for each sensor of the system, one set being
for the visible image, another for the radar return, and the other for the thermal image.
Barott, Coyle, Dabrowski, Hockley, and Stansbury (2014) has found that for the visible
image it will isolate the aircraft, and extract size and shape. The thermal image portion is
the same as the visible image steps except for the fact that the propulsion will be isolated
and the thermal characteristics will be extracted. As for the radar return, it will be
retrieving the distance and orientation of the aircraft. Once all of those components are
compiled, it will then convert the data into a multi-spectral signature, support vector
machine classifier, and then determine aircraft class. Barott, Coyle, Dabrowski, Hockley,
and Stansbury (2014) have put together the best way to determine the maneuverability
and class of aircraft.
9. Augmented Reality Discussion
One way to ensure that the pilot is receiving all of the possible information that
they can, a way to improve awareness is a system of augmented reality. Augmented
reality would be a good addition because it can show objects virtually that may not be

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seen visually with the naked eye otherwise. The Merriam-Webster dictionary defines
augmented reality as, “an enhanced version of reality created by the use of technology to
overlay digital information on an image of something being viewed through a device.”
This technology could be used in conjunction with ADS-B for the cooperative aircraft to
give a visual representation of where the aircraft are in the sky and there direction and
path of travel.
Aero Glass, a company that has already started work on an aircraft augmented
reality system, contains many ways to improve awareness. The features include airports,
navigation aids, Flight Plan route and waypoints, airways, geographic points of interest,
and most importantly ADS-B traffic. Aero Glass’s website shows that other aircraft will
be represented as a point in the sky that is labeled with the tail number of the plane,
altitude, and direction that the aircraft is moving. The overall point of this technology is
not to be a primary way of seeing and diagnosing a problem, but a way of having the
most information of what is going on outside the aircraft.
10. Conclusion
Integration of Unmanned Aircraft Systems in the National Airspace System in the
end is not going to be an overnight affair. The integration of ADS-B, TCAS, Radar, and
EO/IR will take a long time to get simulations, tests, and flight time accrued. ADS-B has
been shown to be the way of the future as it has many features that make it able to sense
where other aircraft are and the main information that is needed to complete the DAA
process. Also, now that ADS-B will be mandatory in 2020, it is definitely going to be a
major part of the DAA systems. Both radar and EO/IR combined will be a great

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combination for tracking non-cooperative aircraft because of the ability to sense the
aircraft’s location, visually identify the aircraft, and see the thermal footprint of the
aircraft and its propulsion system. While there are many other possible combinations for
providing DAA capabilities, this is one of the best combinations and most widely
researched combinations. Now it just comes down to making the technology more
accurate and perfect for integration into everyday use between unmanned aircraft and
manned aircraft.

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