1. Summer 2016 | VOLUME 58, NO. 2
DRONES ARE COMING
– Is the NAS Prepared?
Plus
• One Year of Time-Based Separation at Heathrow
• The Effect of Sun and Solar Winds on Modern Aviation

2. This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic ControlThis article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control

3. UNMANNED AERIAL SYSTEMS
Is the National Airspace System
Prepared?
By Frederick Wieland, Ph.D., Intelligent Automation, Inc.
T
here is no doubt that the future
evolution of the NAS must take
Unmanned Aircraft Systems
(UAS) seriously. The aerospace
community is preparing for such a future.
The RTCA’s Special Committee 228 is
addressing UAS integration in the NAS.
NASA’s UAS Traffic Management (UTM)
program is experimenting with rules for
small UAS at low altitudes. The FAA has
issued its small UAS rule and is work-
ing toward larger scale integration. Various
UAS test sites are running experiments, and
industry is busy developing detect-and-avoid
and other technologies required for integra-
tion. All of these simultaneous preparations
beg a couple important questions: how many
civilian UAS flights will the NAS have to
ultimately handle? And what will be the
implications for the NAS when UAS are
fully integrated?
To address this question, NASA funded
a two-year research study led by Intelligent
Automation, Inc. (IAI), with participation
from Virginia Polytechnic University. The
study forecasted future UAS flight volume
at 2,000 feet above ground level (AGL)
and higher[1]
. The study also estimated
future UAS flight volume, airport and
airspace usage, flight routes, and aircraft
types by interviewing over 50 subject matter
experts (SMEs) representing over 29 civil/
government and industrial organizations
that already use or are planning to use
UAS technology. In addition, IAI scanned
published articles on planned UAS missions
and estimated demand for transportation-
related UAS missions (such as UAS cargo
delivery and air taxi) through socioeconomic
modeling. Finally, IAI investigated what
impact these flights would have on the
existing NAS architecture. In order to
forecast demand, researchers must investigate
the history of UAS demand forecasting,
a field which has a surprising past. The
earliest study found is a 1976 report by
Lockheed Missiles and Space Command for
NASA’s Ames Research Laboratory[2]
. Back
then, UAS were called Remotely Piloted
Vehicles (RPVs). That study interviewed
60 potential civilian users of UAS, and
identified 35 applications of the technology.
Instead of estimating UAS flights, these
and other early studies concentrated on the
total demand for UAVs. The Lockheed
study estimated a demand that translates to
manufacturing 2,000 – 11,000 total UAVs,
with full adoption of the technology by
1985. They noted that the environmental
problems were minimal, and that safety
DmitryKalinovsky;AlexeyYuzhakov/Shutterstock.com
This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control

4. UAS Mission Flts / day Cruise altitude Cruise speed (ktas) Flight duration
Air Quality Monitoring 1,044 4,000 to 6,000 ft. AGL 74 to 89 1 to 4 hrs.
Strategic Wildfire Monitoring 324 31,000 ft. MSL 209 ~20 hrs.
Tactical Wildfire--Maximum 10,432 3,000 ft. AGL 72 to 75 1 to 1.5 hrs.
Tactical Wildfire--Median 2,496 3,000 ft. AGL 72 to 75 1 to 1.5 hrs.
Tactical Wildfire--Minimum 640 3,000 ft. AGL 72 to 75 1 to 1.5 hrs.
Flood Inundation Mapping 127 4,000 ft AGL 46 to 51 1 to 4 hrs.
Law Enforcement 300 3,000 ft. AGL 44 to 51 3 to 8 hrs.
Wildlife Monitoring 308 3,000 ft AGL 44 to 51 ~40 mins.
Aerial Imaging and Mapping 295 3,000 ft. AGL 44 to 51 ~40 mins.
Airborne Pathogen Tracking 1,308 3,000 to 10,000 ft. AGL 72 to 97 1 to 4 hrs.
Maritime Patrol 1,512 5,000 to 35,000 ft. AGL 151 to 343 4.5 to 14 hrs.
Border Patrol 867 5,000 to 15,000 ft. AGL 129 to 173 2 to 7 hrs.
Weather Data Collection 2,401 5,000 to 35,000 ft. AGL 151 to 343 1.5 to 13 hrs.
News Gathering 875 1,500 to 3,000 ft. AGL 45 to 51 15 mins. to 2 hrs.
Point Source Emission Monitoring 432 3,000 ft. AGL 72 to 80 40 to 300 mins.
Table 1. Partial list of UAS missions analyzed
was not an issue other than the need for
effective collision avoidance systems. Three
years later, a study by NASA Wallops Flight
Center identified several UAS aircraft
designs that could accommodate most of the
missions envisioned at that time[3]
.
Between 1974 and 2000, there were
about 19 UAS public reports sponsored by
NASA. Between 2000 and 2015, there were
over 90 studies involving UAS, with over a
quarter of them published since 2013. This
only covers studies funded by NASA.
In a precursor to the present study,
IAI started with the RTCA’s DO-320
document, produced by RTCA’s earlier
SC-203 Committee involved in UAS
integration in the NAS[4]
. That document
echoed Lockheed’s earlier study but was
significantly more detailed. In addition to
estimating the number of vehicles required to
satisfy the UAS mission demand, it provided
UAS vehicle projections for specific markets
(defense, civil/government, and commercial)
and also specified how to fly particular
missions. Using that study, IAI quantified
the vehicle production numbers into flights.
This type of translation is a difficult task and
involves assumptions regarding the percent
of time each vehicle is used, the number
of vehicles required per mission, mission
duration, and flight path. By estimating
these quantities, IAI computed that, above
2,000 feet, there would be around 30,000
to 35,000 UAS flights per day in the NAS.
This volume seemed very high, and hence,
IAI embarked on the present study, a more
detailed mission-by-mission look into the
actual flights required.
What Kind of Missions Were
Considered
In the present study, IAI started with the list
of UAS missions that were identified in the
RTCA DO-320 document[4]
. IAI purposely
excluded missions below 2,000 feet AGL
and instead focused on those UAS missions
that would potentially interact with commer-
cial aviation. The popular package delivery
and so-called “taco delivery” flights that
have been highly publicized in the media,
along with the quadcopter drones that are
available today in every electronics outlet,
were purposely excluded from the present
study because their potential interaction with
piloted flights is minimal. For the remaining
missions, IAI surveyed potential users for
some missions and used socioeconomic mod-
eling for those remaining missions that were
transportation-related.
The first surprise was that all civil/gov-
ernment agencies that IAI contacted actually
already had a group to work out all the logis-
tics of using UAS technology for their par-
ticular missions. Through interviews with
the SMEs, IAI was able to compile a data-
base of UAS missions, UAS aircraft type,
payloads, mission altitude, mission duration,
flight path, departure and arrival airports,
and the approximate local time when the
mission would take place. The SMEs point-
ed out that some missions would involve sev-
eral flights over the span of several days. IAI
compiled all of this information in a database
of likely UAS flights in the NAS at or above
2,000 feet AGL.
The surprises continued. Many mis-
sions had subcomponents which were previ-
ously undocumented. For example, consider
the National Forest Service’s proposed for-
est fire fighting missions. When a wildfire
of sufficient magnitude breaks out with
the potential to affect population centers,
efforts begin to fight the fire. The SMEs
identified two scenarios to employ UAS in
firefighting. In the first, the UAS weaves in
and out of the fire zone, not only collecting
information but also fighting the fire itself.
In a second, more constrained scenario, the
UAS flies on the boundary of the fire to
avoid interference with piloted flights and
firefighters on the ground. In this second
scenario, helicopters dropping fire-retard-
ing borate and fixed-wing vehicles dropping
water fly in and out of the affected locations.
In addition, there may also be news helicop-
ters hovering around shooting video. Even
though it is a busy little airspace, the area
could be managed through the issuing of a
Temporary Flight Restriction (TFR) so that
commercial and GA aircraft avoid the area.
So at first glance, it appears that firefighting
will interact with NAS traffic minimally,
only through TFRs.
But the story does not end there. In
addition to tactical wildfire monitoring, stra-
tegic monitoring is of great interest, whereby
UAS can pinpoint the location of wildfires in
their incipient stage. As there are more than
UNMANNED AERIAL SYSTEMS
This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control

5. 50,000 wildfires per year in the continental
United States (CONUS), these missions are
critical. The National Forest Service plans
to fly orbiting, long-endurance UAS with
the appropriate sensors at high altitudes
(more than 27,000 above feet mean sea level
[MSL]) that collectively cover the entire
CONUS during peak fire season. These
flights are continuous – when one aircraft is
low on fuel, another aircraft is launched and
UNMANNED AERIAL SYSTEMS
takes its place. Their orbit places them in the
altitude band of cruising commercial traffic.
Yet another intriguing mission is
weather data collection. Currently, there are
some commercial organizations with weather
Figure 1. Differences in performance between a B737 aircraft and several UAS aircraft
This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control

6. sensors installed on commercial aircraft. The
data is highly valuable to weather researchers
and helps improve the quality of weather
forecasts. However, commercial aircraft have
very low density in some areas such as the
upper Midwest, and in any event, they sample
the atmosphere only in discrete locations
determined by existing airways, at discrete
times determined by flight schedules, and
at altitudes only along their climb, cruise,
and descent profiles. To create a data-rich
environment, forecasters envision UAS will
fill in the gaps. One mission design calls
for flights that porpoise or fly up and down
through multiple altitude bands, through the
atmosphere, flying up and down to sample
atmospheric states from 5,000 to 35,000 feet
AGL. These flights operate continuously,
with one aircraft replacing another that is
low on fuel. Other missions that include
porpoising flights are maritime monitoring,
border patrol, and air quality monitoring.
Those who monitor air quality will
also find value in UAS. Air quality today
is measured with an array of technologies,
including sensors on the ground and on
tops of buildings, weather balloons, satel-
lites, mobile ground sensors, and mandato-
ry industry reporting of noxious emissions.
These sources vary in their cost, accuracy,
and airspace coverage; UAS technology will
help fill in the gaps (and perhaps replace
these sources entirely). However, the areas
that require the most extensive monitoring –
such as Southern California – are also areas
of dense arrival/departure traffic to busy air-
ports. UAS flights monitoring air quality in
those areas would have to remain well clear
of commercial flights while also providing
the high-resolution, data-rich information
needed by atmospheric scientists. Outfitting
aircraft with air quality sensors for the arriv-
al/departure corridors will help accomplish
this goal, augmented with UAS aircraft to
sample outside these corridors. Based on the
SME survey, IAI computed that over 1,000
additional air quality sampling flights per
day are needed across CONUS, assuming
that the commercial flights continue to mon-
itor air quality.
IAI also discovered new UAS missions
that had been largely absent in previous
studies. The FAA is required to inspect each
ground navigation aid periodically by flying
an aircraft to sample the signal strength
around the navigational aid. Currently, this
procedure is done with small, piloted aircraft
but could be completed more cost-effectively
in the future using UAS aircraft.
Airborne pathogen tracking is a mission
where UAS aircraft search the atmosphere
for pathogens, which can travel across geo-
graphical areas on atmospheric particulates
and water vapor. Tracking such pathogens
will allow the medical community to study
the spread of disease. The unanswered ques-
tion is, if IAI found two new missions during
this brief study, and UAS technology has yet
to be applied on a large scale, how many new
(currently unknown) missions might ulti-
mately benefit from UAS technology?
Translating the SME and socioeco-
nomic data for each of the 19 missions into
daily flight counts resulted in an estimate
of 26,312 flights per day in the NAS. This
result is a bit lower than the earlier estimate
using the RTCA DO-320 data, but IAI has
more confidence in the current estimate. A
partial list of the missions – 13 of the 19 ana-
lyzed – is shown in Table 1 (page 26).
Implications of UAS on the NAS
Architecture and Controllers
There are approximately 45,000 controlled
flights per day in the NAS, roughly 34,000
commercial flights and 11,000 GA flights.
These numbers have generally increased
slowly with time and vary by day of week
and time of year. They also fluctuate, as
they are affected by macroeconomic trends.
Adding an estimated 25,000 UAS flights
into the NAS will increase this nominal
flight count by 55 percent – a significant
increase in workload. Even under the best
circumstances, these additional UAS flights
will ramp up from near zero to the estimated
maximum over a period of many years, so
there will be time for the NAS to adjust. But
can the current NAS architecture handle
this additional volume of UAS flights, or are
changes needed?
The short answer is that there will
be significant problems at this higher vol-
ume level. For starters, the current Traffic
Flow Management (TFM) system relies on
Monitor Alert Parameter (MAP) values to
estimate the maximum number of simultane-
ous flights that may be in a controller’s sector
at any time. The MAP numbers are based on
averages of flight times through controlled
sectors. But some UAS missions orbit an area
over an extended period of time, and thus will
permanently occupy a sector slot, reducing
sector capacity and denying some commercial
aircraft entry into the sector.
A second problem is that some
proposed missions, as mentioned earlier,
have flights that porpoise while also
maintaining a permanent presence in the
system. Weather data collection porpoising
occurs from 5,000 to 35,000 feet MSL
UNMANNED AERIAL SYSTEMS
Figure 2. Projected UAS flight density, in flights per 10 x 10 statute mile (nm) grid, at ZNY by local time of day
This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control

7. in order to fully sample the atmospheric
state. Flying vertically through multiple
flight levels will cause additional controller
cognitive complexity that will further reduce
en route capacity.
A third problem is that the UAS air-
craft add performance variability that con-
trollers must manage. Figure 1 shows the
difference in climb and cruise performance
between a standard Boeing 737 (B737) and
two large 737-type UAS aircraft (one similar
to a Global Hawk and another similar to a
Predator). The UAS aircraft performance
was derived from an earlier IAI study by to
quantify UAS performance, with the help
of UAS manufacturers, for fast-time mod-
eling [5]. The charts reveal that the climb
and cruise performance of a B737 is much
different (and superior) to that of large UAS
aircraft. The cruise speeds, in particular, of
UAS aircraft are between 25 to 50 percent
slower than the B737.
Obviously, the complexity of a con-
troller’s job increases substantially with the
introduction of UAS missions. Sector capac-
ity is compromised when orbiting UAS are
present. Controller cognitive understanding
of the situation becomes increasingly com-
plex with porpoising flights and UAS air-
craft that fly significantly slower than their
commercial counterparts. UAS flights will
also add at least 50 percent more volume to
the NAS than currently experienced.
To quantify some of these concerns,
IAI ran some system-wide studies using
the data. Figure 2 shows the projected UAS
flight density at New York Air Route Traffic
Control Center (ZNY) by local time of day.
The counts were computed by overlaying
10 by 10 nm grids on ZNY’s airspace and
counting the maximum number of UAS
flights in each grid per hour. The maximum
densities across all grids were then averaged
to produce the chart. The data suggests that
one to three UAS flights per 10 by 10-mile
grid can be expected during the course of
a day at ZNY. Other centers show similar
results. This calculation suggests that UAS
flights will significantly reduce sector capac-
ity. These capacity reductions are present in
every center in the NAS, as the projected
UAS flights are ubiquitous.
One easy solution might be to segre-
gate UAS aircraft into different air corridors
that can be separately controlled. While this
solution may work well for low altitude mis-
sions (below 500 feet AGL, for example),
it is problematic for higher altitude UAS
flights. Quoting from Lockheed Martin’s
1976 report on UAS flights (called RPVs in
the report):
One way to minimize the danger of colli-
sion between RPVs and other aircraft is to
assign restricted airspace to RPVs and try
to keep other aircraft out. Except in lim-
ited and specialized situations, this is not
a desirable approach. Most of the missions
for which RPVs appear promising do not
lend themselves to this approach. (refer-
ence, page 14). [2]
Based on interviews with SMEs, IAI
agrees with this viewpoint. Another possibil-
ity for handling UAS is to give priority access
to the commercial flights and delay, or deny,
access to conflicting UAS missions. While
it may be tempting to delay or postpone a
weather monitoring mission, for example, so
that a sequence of commercial flights can pass
through the airspace unimpeded, the coun-
terargument is also very powerful – although
delaying an airline’s flights in favor of UAS
flights will increase airlines’ costs and create
passenger delay, there may be (at most) a few
thousand passengers and a dozen or so airlines
immediately affected. In contrast, the UAS
mission provides data-rich weather informa-
tion for the 300-plus million people who are
not flying that day. From an overall bene-
fit-to-society argument, the UAS missions may
be more important than the commercial flights.
From a transportation viewpoint, the commer-
cial missions may be much more important.
These conflicting perspectives may create a tug-
of-war as UAS flight volume grows.
The Main Problem with the
Current NAS Architecture
The main impediment to UAS flights in the
NAS today is rooted in the transportation
model that motivated the current design.
The airspace is viewed as a mode of trans-
portation for people and goods, and therefore
the airports, sectors, terminal radar approach
control facilities (TRACONs), and airspace
rules are all oriented towards efficiently pro-
cessing transiting aircraft in an assembly-line
fashion. With the introduction of UAS, the
airspace has a broad array of entirely new
uses unrelated to transportation. These new
uses conflict with the traditional design
of the airspace, requiring a re-thinking of
the NAS architecture in order to efficient-
ly accommodate both uses. The problem is
well beyond detect-and-avoid, communica-
tion frequency congestion, or UAS security.
All of these other problems are important
issues that must be solved before UAS can be
effectively integrated in the NAS. However,
even if these other problems are solved
soon, the NAS architecture remains an
impediment for handling the projected UAS
flight volume, and will itself constrain the
growth of the UAS industry and its potential
commercial applications.
Finally, the validity of these data
should be assessed. How confident are we
that these flight counts are valid? Since IAI
consulted with SMEs currently planning
UAS missions – many of whom are already
conducting such missions under FAA-
issued Certificates of Authorization – IAI
is fairly confident that these numbers are
representative of what may happen. If there
is any error, IAI believes the error is on the
downside, that IAI estimated too few UAS
flights, because there are some missions
excluded due to the study’s scoping con-
straints and the fact that new missions are
proposed periodically. But even if IAI is too
high by a factor of two – that only 12,500
flights per day will occur in the airspace –
that will nevertheless add 25 percent more
flights to the NAS; therefore, all the issues
mentioned earlier would still be in play. In
IAI’s opinion, the current NAS architecture
is unprepared for the introduction of UAS
flights and the accompanying variability and
uncertainty that they create.
For more information on the projected
UAS flights, visit www.i-a-i.com/?product/
uas-max.
References
[1.] S. Ayyalasomayajula, R. Sharma, F. Wieland,
A. Trani, N. Hinze and T. Spencer, “UAS
Demand Generation Using Subject Matter
Expert Interviews and Socio-economic Analysis,”
AIAA Aviation 2015, Dallas Ft. Worth, Texas,
June 2015.
[2.] J. R. Aderhold, G. Gordon and G. W. Scott,
“Civil Users of Remoted Piloted Aircraft
Summary Report,” Lockheed Missiles & Space
Company Inc., Sunnyvale, CA, July 1976.
[3.] M. B. Kuhner and J. R. McDowell, “User
Definition and Mission requirements for
Unmanned Airborne Platforms,” NASA Wallops
Flight Center, December, 1979.
[4.] Radio Technical Committee for Aviation
(RTCA), “Operational Services and
Environmental Definition (OSED) for
Unmanned Aerial Systems (UAS),” RTCA,
Washington, DC, June 10, 2010.
[5.] F. Wieland, S. Ayyalasomayajula, R. Mooney,
D. DeLaurentis, V. Vinay, J. Goppert, J. Choi
and G. Kubat, “Modeling and Simulation for
UAS in the NAS,” NASA Technical Report
CR-2012-NND11AQ74C, Washington, DC,
September 2012.
UNMANNED AERIAL SYSTEMS
This article originally appeared in the Summer 2016 issue of The Journal of Air Traffic Control