Design of a Flight Planning System to Reduce
Persistent Contrail Formation
Jhonnattan Diaz, David Gauntlett, Harris Tanveer, PoCheng Yeh
Sponsored by Center for Air Transportation Systems Research
and Metron Aviation
George Mason University, Department of Systems
Engineering and Operations Research
Abstract— During flight, airplanes emit greenhouse gases as
well as water vapor and other byproducts. Although water vapor
itself is not a greenhouse gas, it can combine with soot and other
particles to create condensation trails (contrails) that persist, or
stay in the atmosphere for unusually longer periods of time,
having a net effect on radiative forcing that may be three or four
times worse for the planet than carbon dioxide emissions. The
uncertainty on the actual effect of contrails is also very high in
comparison to the effects of other greenhouse gases because of a
relative lack of scientific understanding.
Contrails are more likely to persist in specific weather
conditions in the upper troposphere in areas known as Ice Super
Saturated Regions (ISSR). Contrails are also likely to persist for
as long as the ISSR exist, and stay in the area unless wind shear
or other such weather conditions dissipate the contrails.
In this study, operational changes are being studied to change
aircraft trajectory to avoid ice supersaturated regions by
conducting horizontal, vertical, and a combination of the two
maneuvers to avoid ISSR. A system is being designed to compare
the miles of contrails that are formed as well as the fuel that is
burned when a contrail avoidance flight plan is used as opposed
to a normal flight plan.
I. INTRODUCTION
A. Global Climate Problem
The World Health Organization (WHO) projects the world
population reaching to 10 billion humans by the year 2100 [1].
With an increasing world population, it can be assumed that the
global energy demand will increase, causing the increased
burning of fossil fuels. Fossil fuels, when burned, produce
greenhouse gasses such as carbon dioxide that can stay in the
atmosphere for centuries and cause higher global temperatures.
The increase in global temperatures causes phenomena such as
melting ice caps in the arctic, mean seal levels rising, and
erratic weather patterns. The following graphic summarizes the
aforementioned information.
Figure 1: Global climate change occurs from the factors listed on top and can
manifest itself by the factors listed on the bottom
B. Air Travel Demand
With an increase of air travel in the United States, there has
been more attention drawn to the environmental impact on the
use of aircraft in the National Airspace System [Waitz et. al.
2004]. The following graphic indicates the general trends of the
demand for air travel from 1996 to 2012. The demand in 1996
was for 7,289,449 flights per year. By 2012, there was a
demand for 8,441,999 flights - indicating more than a 15%
increase in the demand for air travel from 1996.
Additionally, with an increased in demand, there has also
been an increase in the amount of fuel consumed by aircraft.
From 1977 to 2012, there has been an increase of over 26% for
the amount of fuel that aircraft use. While an airline’s primary
goal is to increase profits over time, part of an ethical
responsibility involves understanding the environmental effects
caused by air traffic.
C. Air Traffic Control
The Federal Aviation Administration has designated
Federal Airways (FARs) that are decomposed into 2 categories:
Very High Frequency (VHF) Omnidirectional Range (VOR),
and Colored Airways. The latter is only used in Canada,
Alaska, and coastal areas. VORs are predominately used
within the continental United States and were established in
1950’s for aviation navigation [21].
VORs are subdivided into low altitude designated (Victor
airways) areas that covers the range of air space between 1,200
- 17,999 feet above Mean Sea Level (MSL) classification.
Class A airspace covers high altitude designated Jet Routes
between 18,000 – 45,000 feet above MSL. The idea is that after
an aircraft reaches Flight Level 18+ (18,000 feet above MSL),
it will be passing through different VORs along the way until
they start the arrival descent towards the airport through the
Terminal Radar Approach Control (TRACON). However, a
new structure of operations is being studied where in the very
near future there is a High Altitude Redesign (HAR) project
that will provide pilots with ample flexibility in the way they
fly the aircraft once they reach the en route/oceanic phase of
cruise altitude to fulfill their needs [21].
D. Aircraft Emissions
With the increase of air traffic, and in turn, an increase of
the amount of fuel that is being consumed, more attention has
been drawn towards aircraft-induced environmental effects
[Waitz et. al. 2004]. The process of the combustion of jet fuel
produces carbon dioxide, sulfer oxides, soot, hydrocarbons, and
nitrogen oxides. The following graphic displays the chemical
process involved in the combustion process in addition to the
global impacts and damages.
exhaust gas mixture with ambient temperature and humidity.
At cruising altitudes (between 21,000 feet and 41,000 feet), the
exhaust mixture freezes, forming ice particles upon contact
with the free air, leading to visible contrail formation.
Generally, contrails created through the aerodynamics of an
aircraft fade within two to three wingspans of an aircraft.
Persistent contrails with longer lifetimes and larger horizontal
extent are caused in ice supersaturated regions (ISSR) in the
upper troposphere with relative humidity levels greater than
100% and temperatures below -40 degrees Celsius. Persistent
contrails may affect both the radiation budget and climate in a
manner similar to natural cirrus clouds.
Persistent contrails are believed to be responsible for the
incremental increase of trapped solar radiation in the earth’s
surface, which contributes to the effect of global warming.
Recent reports [3] state that persistent contrails may have a
three to four times greater effect on the climate than carbon
dioxide emissions in a short time horizon (10-20 years).
Greenhouse gasses are in the atmosphere for longer periods of
time relative to contrails, [18] therefore allowing the gasses to
mix in the atmosphere, having the same concentration
throughout the world. Contrails on the other hand, provide
more regional affects since they occur only in select areas of
the troposphere that fulfill the conditions for persistent contrail
formation.
The following image displays the net warming effects that
aviation has on the earth in terms of radiative forcing. From
this Government Accountability Office document, it can be
noted that contrails have a net radiative forcing affect that
exceeds the effects of carbon dioxide [16].
Figure 2: Jet A fuel combustion and products
It is evident from the above graphic that impacts of aircraft
emissions can create global climate effects in terms of changes
in temperature. The effect of aircraft emissions on the Earth’s
climate is one of the most serious long-term environmental
issues facing the aviation industry (IPCC, 1999; Aviation and
the Environment – Report to the United States Congress,
2004). Estimates show that aviation is responsible for 13% of
transportation-related fossil fuel consumption and 2% of all
anthropogenic CO2 emissions [14]. The transportation
industry as an entirety is responsible for 28% of CO2
emissions in the United States.
E. Contrails
In 1992, linear condensation-trails, otherwise known as
contrails, were estimated to cover about 0.1% of the Earth’s
surface [22]. The contrail cover was projected to grow to 0.5%
by 2050. Contrails contribute to warming the Earth’s surface,
similar to thin cirrus clouds formed in the troposphere and have
an important environmental impact because they artificially
increase the cloud cover and trigger the formation of cirrus
clouds; thus altering climate on both, local and global scales.
Persistent contrails form cirrus clouds made of water vapor
from engine exhaust or the aeroydynamics of a jet aircraft. The
initial formation of the persistent contrail originates from
Figure 3: Contrails have a lower scientific understanding than CO2. As a
result, the variability on the actual radiative forcing effects is high.
It should be noted that the radiative forcing due to contrails
may be higher than the radiative forcing due to carbon dioxide
(CO2) emissions.
Because of the lower scientific
understanding regarding contrails as compared to other
greenhouse gasses, the true effects of contrails remain
unknown- as depicted by the large variance bars.
Furthermore, contrails can also induce cirrus clouds, therefore
having another indirect impact on the radiative forcing levels.
II. STAKEHOLDER ANALYSIS
After careful consideration and strenuous research for
designing a system to manage and create new and optimal
flight plans for contrail neutrality by 2020, the group has
identified the stakeholders that will be involved and impacted
with the implementation of the Flight Planning System (FPS).
The stakeholders are the Federal Aviation Administration
(more specifically the Air Traffic Organization department),
airline management for airlines utilizing the National Air Space
(NAS), the consumers of air travel, and other citizens
concerned about climate change.
A. Federal Aviation Administration- Air Traffic Organization
Under the umbrella of the Federal Aviation Administration
(FAA), there is a complex network that is constructed for the
operations of everyday commercial aviation in the National
Airspace System (NAS). A major component of this network
is composed of the Air Traffic Organization (ATO), which
operates facilities such as Air Traffic Control System
Command Centers (ATSCC), Air Route Traffic Control
Centers (ARTCCs), Terminal Radar Approach Control
Facilities (TRACONs), and Air Traffic Control Towers
(ATCTs). The branches of the Air Traffic Organization (ATO)
are necessary to perform essential services starting from the
flight plan to the takeoff of the aircraft following through all
the way to the final descent of the aircraft. The primary
objective of the ATO and all its branches is to ensure safe and
efficient transportation in the increasing density of the National
Airspace System [21].
B. Airlines-Airline Management
Although it is in the best interest of an airline to provide
users (customers) with safe transportation, airlines exist
primarily to make a profit. Their main concern is to provide
customers with faster flight times at lower operational and fuel
costs. At the same time, for the continuity of operation, airlines
are subjected to regulations set forth by the FAA.
This is an important aspect given the trends of rising oil prices,
rising demand for air travel, and rising operating cost for airline
companies.
Another objective of the ICAO is to promote environmental
policies taking into consideration technological factors
pertaining engine emissions. Emissions are increasingly
becoming a topic of interest given the rising levels of
greenhouse gas emissions, and the potential of contributing to
global warming. The ICAO is mitigating these problems with
the help of restructuring operational procedures, and with the
help of financial tools is studying the possibilities of moving
towards a carbon market based trading market.
E. Stakeholder Tensions
The primary goal of the Air Traffic Organization is to
maintain a determined level of safety for the successful air
travel operations within the National Airspace System. The
airline management’s main goal is to maintain financial
viability while satisfying user demand. Additionally, customers
(citizens/public) demand safe transportation, with minimal
monetary costs for air travel.
Although there is a high degree of communication and
collaboration amongst these stakeholders, undoubtedly there
will be conflicts along the workings of all operational agencies
that encompass the model of transporting passengers safely,
efficiently, and in an environmentally conscious manner in
order to come up with a cohesive solution to the problem of
contrail neutrality.
The following graphic displays the interactions between the
stakeholders. The general public would support attempts to
reduce contrail formation because of the negative climate
impacts associated with radiative forcing. Airlines would
potentially be against any system reducing contrail formation
because of possible increased operational costs.
C. Citizens and Climate Change Advocates
Because the effects of condensation trails exist mainly on a
regional level, citizens and climate change advocates may be
concerned about the net heating conditions in their particular
areas contributing to global warming. Additionally, with the
rerouting of aircraft, citizens may be concerned with noise and
other forms of pollution from aircraft flying at lower altitudes
over their houses.
D. International Civil Aviation Organization (ICAO)
The International Civil Aviation Organization (ICAO) is an
agency developed by the United Nations that sets standards and
regulations for the safety and efficiency of international air
space. Currently, the ICAO is comprised of 191 countries that
promote security and environmental protection all around the
world.
Apart from the safety and efficiency objectives, another
main goal of the ICAO is to develop a sustainable business
model that would enable it to construct a policy framework that
would impart a systematic strategy for a sustainable enterprise.
Figure 4: Stakeholder Interactions
F. Win-Win Situation
In order to create a system to satisfy all three primary
stakeholders, there needs to be a solution that reduces fuel
consumption, environmental impact, and maintains the same
level of safety desired by the Air Traffic Organization (ATO).
From the perspective of the general public, the only way to
create new legislation regarding environmental concerns is
through the legislative branch of the United States of America.
These legislations may mandate government agencies such as
the Department of Transportation, Environmental Protection
Agency, and the Department of Energy to execute any
necessary measures.
In 1970, Congress passed the Clean Air Act (CAA) when
evidence was provided regarding pollutants through airborne
contaminants that can affect the health of citizens.
Under the CAA, federal and state laws are able to enforce
emissions from different sources such as factories and cars.
Although Title 42 of the USC Chapter 85, subchapter II of the
Clean Air Act has numerous descriptive standards and
benchmarks for emissions for motor vehicles, the broad
language and vague delineation of aircraft emission standards
has left the aviation industry with very little emission
regulations.
Because aircraft emissions are a global problem
organizations such as the International Civil Aviation
Organization (ICAO) aim to create cooperative decisions on a
global scale. In 2008, the European Union (EU) decided to
independently regulate greenhouse gas emissions from aircraft
by means of an Emission Trade System (ETS) in order to
decrease the CO2 emissions produced by all aircraft leaving
and entering the EU. By 2012, president Obama and Congress
signed a law prohibiting any type of participation of any EU
mandates. As it is becoming apparent, there is a lack of
uniformity of who should regulate greenhouse gasses and how
regulations would be mandated and implemented throughout
the globe. This realization is the main objective of the win-win
situation for the stakeholders (specially the airline industry) in
the Design of a Flight Planning System to Reduce Persistent
Contrail Formation.
In creating such a system, legislation can be enacted to
regulate standards for new engines, existing engines, airframes,
as well as operational standards. For new technology, the
innovation of engine design and airframes will deliver
efficiency and close the gap of greenhouse gas emissions.
However, for existing aircraft engines, the continued level of
fuel burn will hinder the goal of carbon neutrality.
Operational standards provide a cost effective and rapid
incorporation of testing that will be beneficial as a first step
approach to greenhouse gas emissions. Another aspect is to
promote regulatory tools such as Carbon Emission Trading that
will allow the EPA to regulate emissions, and move towards a
system that would be uniform in conjunction with measures
taken by the EU and in the near future (2020) to be adopted
around the world with the facilitation of the ICAO [2].
Adopting and enforcing rigid guidelines and regulations from
the federal government on airlines will impose great
compliance costs (such as increased fuel costs) not only on
airlines, but regulatory agencies, and the general public
demanding environmental change by means of taxes and
tariffs. As economists are studying different alternatives, they
are in consensus that a less rigid, and more “flexible” approach
to this issue would enable the stakeholders to gradually adapt to
a new system. Economists have been studying the .EU’s ETS
for some time and can see the value on emissions trading as the
best cost effective for all parties to adopt. Because aviation’s
environmental impact is global, airlines have to become more
open to the idea of environmental responsibility as a whole,
and economists believe that the most cost-conscious approach
to flexible regulation will be a market based economy based on
the global trade of pollutants.
III. PROBLEM AND NEED STATEMENTS
A. Gap Analysis
The group has determined that there are three major driving
factors that can have significant impact on the contrail
coverage in the sky. The first driving factor is the number of
aircraft demand in the sky (at cruise altitude). In addition to the
air traffic density, the quantity and types of engines being used
may have a significant consequence on the coverage of
contrails. The third driving force for contrail coverage is
regarding the temperature and humidity conditions existing in
the cruising altitude.
Keeping these driving factors in mind, it has been
determined that the goal of the project is to reduce the radiative
forcing due to contrails to 7.06 mW/m^2 as depicted in the
following graphic. The blue curve represents the projected
radiative forcing due to contrails up to 2050. The red line
depicts what the group has decided to call a “contrail neutral”
level. The logic behind this gap analysis follows from the
International Air Transport Association’s pledge to reduce
carbon emissions to obtain carbon neutrality by 2020 to a
baseline level of 2005. For the contrail neutral scenario, a 2005
baseline has been specified at 7.06 mW/m^2, and the system’s
goal is to drive the estimated radiative forcing curve down to
that value by 202, the same time IATA pledges to obtain
carbon neutrality.
Figure 5: Gap quantifying radiative forcing due to contrails. This gap may be
closed by reducing the miles of contrails.
In order to decrease the amount of radiative forcing due to
contrails, any system would have to decrease the miles of
contrails that are produced as the aircraft travels through ISSR.
Decreasing the miles of contrails decreases the percentage of
contrail coverage over the NAS, which would then decrease the
effects of radiative forcing. The goal of this project is to reduce
the miles of contrails that are formed, to indirectly reduce the
radiative forcing levels.
B. Problem Statement
With an increase in the demand for air travel resulting in
the environmental impacts discussed in the Context Analysis,
there is also a need for determining flight paths to reduce the
amount of persistent contrails that can form. Currently there is
no existing system that provides flight paths for aircraft to
avoid Ice Supersatured Regions (ISSR) while accounting for
the tradeoffs between fuel consumption, the amount of time
aircraft are in the air, as well as the miles of contrails that are
formed by ISSR avoidance flight plans.
C. Need Statement
In order to solve the problem of radiative heating due to
contrails, the ultimate goal of the project is to design a system
for the user to create a flight plan that reduces persistent
contrail formation while taking into consideration the tradeoffs
of fuel consumption and airspace demand.
without taking any avoidance measures into account. The flight
path is routed along the shortest route possible between the two
airports which results in a straight line.
B. Airway (Historical) Route
The system will have access to previous flight data. By
using this historical flight data the system is able to test the
flight path that is regularly taken by the aircraft. Including this
route allows the system to compare to other trajectories.
C. Vertical Path Adjustment
This path adjustment/contrail avoidance method will adjust
the aircraft's altitude in order to avoid flying through the
contrail producing region. Temperatures tend to increase as an
aircraft travels higher into the troposphere- the layer of the
atmosphere that is used as the cruising altitude. Therefore,
decreasing an aircraft’s altitude may place the aircraft at an
altitude that is not as likely to create contrails because of the
temperature and humidity thresholds.
IV. DESIGN ALTERNATIVES
Contrail formation frequency heavily depends on the
weather and humidity in the cruising altitude (troposphere 1012 km) [1]. The flight path adjustment alternatives provide a
flight paths that avoid regions in which an aircraft is prone to
creating persistent contrails. The goal of the system is to
provide a strategic flight plan for each individual commercial
flight. The input of the system is the integration of the Rapid
Refresh (RAP) weather system developed by the National
Oceanic & Atmospheric Administration (NOAA) and historical
flight paths obtained from the Federal Aviation Administration
(FAA). The flight path computation for the aircraft involves
using humidity and temperature provided by the RAP database
to calculate areas with a relative humidity with respect to ice
(RHi) that is greater than or equal to 100% [13]. The system
will also perform a tradeoff between creating a flight path, the
fuel consumption, as well as the amount of emissions in the
creation of an optimal flight path.
The following diagram shows the different flight path
alternatives considered by the system. Each is described below
the diagram.
Figure 7: Vertical maneuvering for ISSR avoidance
D. Horizontal Path Adjustments
The horizontal adjustment flight path maneuvers the aircraft
in a horizontal direction by traveling around the regions where
there is a high likelihood of contrail formation. With this
directional change, the heading and banking angles change,
which optimal cruising altitude is maintained for fuel
consumption. The shortest route in maneuvering horizontally
to avoid contrail formation is maneuvering at each local
minimum tangent to the point of the circular region of
avoidance.
Figure 8: Horizontal maneuvering for ISSR avoidance
Figure 6: Five alternatives for flight path design
A. GCD Route
The first route considered by the system is the great circle
route. This route is the most optimal for the aircraft to fly
E. Combination of Vertical and Horizontal
This flight path will allow the aircraft to maneuver through
varying altitudes as well as horizontally depending on the
likelihood of contrails forming at a particular region. The
system will also take into account the tradeoff between fuel
and carbon dioxide emissions (the team is currently working
on finding the proper threshold for tradeoff).
This allows the system to be scaled up to test large numbers of
aircraft.
F. Value Hierarchy
The utility of each alternative route will be studied with the
following values in mind:
B. Contrail Avoidance Router
Ice Supersaturated Regions, (ISSRs) will be treated as a
binary value. Each region will either cause persistent contrails
when an aircraft flies through the region, or the region will not
form persistent contrails when an aircraft flies through it. Once
the weather data has been broken down into a matrix of 1’s and
0’s, the system can determine routes that take into account
contrail avoidance. It must be considered that when avoiding
contrails, some amount of fuel will need to be burned in order
to fly the extra distance required by these routes than by the
GCD, and perhaps the actual flight path routes. Due to this,
three different avoidance methods are being considered as
mentioned in the alternatives section.
Figure 9: Value hierarchy to evaluate each alternative
The best anticipated alternative flight path is a path that
consumes the least amount of fuel, has the shortest flight
duration, and makes the least miles of contrails. Aircraft
spacing safety is an important value for the system; however,
safety will be handled by air traffic control, not the system.
By the end of SYST 495, the group will have constructed a
utility vs. cost graph for each alternative route to evaluate the
best alternative.
V. METHOD OF ANALYSIS
A. Simulation
The following diagram shows the various inputs and
outputs to and from the simulation.
Design of Experiment
In order to determine the effects of the different route
alternatives on contrail formation, the following experiment
will be conducted.
The great circle distance route will be used as a control, or a
baseline for the experiment. The independent variable, or the
different flight routes, (airway route and three contrail
avoidance routes) will be tested using 24 hours of flight data
and thirty days of weather data. Each aircraft will be flown
through the system following each of the different flight path
alternatives and the following dependent variables will be
studied:
 Fuel consumption
 Flight duration
 CO2 emissions
 Total miles of contrails formed
A tradeoff analysis will be completed between each of the
aforementioned dependent variables to comprehend the utility
for each route versus cost as described in the Value Hierarchy
section.
VI. RESULTS
TBD
Figure 10: High level input/output for the simulation
The inputs to the system are two databases- Rapid Refresh
database (RAP) available from NOAA and the flight schedules
obtained through a FAA flight tracker system. The simulation
then uses four different mechanisms in order to produce the
total flight time, total fuel used, and total miles of contrails
formed for each of the alternative routes. These routes are
explained in greater detail later with regards to the simulation,
but are the great circle distance, actual flight route, horizontal
avoidance method, altitude avoidance method, and a
combination of horizontal and altitude avoidance method. The
main controller of the simulation is the simulation controller.
The simulation controller then calls upon the other three
mechanisms as required. When the simulation is ready for new
data, the database handlers are called. When the system has
the data needed to test a flight, the flight object will be called.
VII. RECOMMENDATIONS AND CONCLUSIONS
TBD
ACKNOWLEDGMENT
We wish to acknowledge the special contributions of Dr.
Lance Sherry, Mrs. Paula Lewis, Mr. Akshay Belle, Dr. Terry
Thompson, and Mr. Adel Elessawy for this project.
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