Paper Title (use style: paper title)



Design of a Flight Planning System to Reduce Persistent Contrail Formation

Jhonnattan Diaz, David Gauntlett, Harris Tanveer, Po-Cheng Yeh

George Mason University, Department of Systems Engineering and Operations Research

Sponsored by Center for Air Transportation Systems Research and Metron Aviation

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.

Introduction

1 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.

[pic]

Figure 1: Global climate change occurs from the factors listed on top and can manifest itself by the factors listed on the bottom

2 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.

3 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].

4 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.

[pic]

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.

5 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 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].

[pic]

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.

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.

1 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].

2 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.

3 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.

4 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. 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.

5 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.

[pic]

Figure 4: Stakeholder Interactions

6 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.

Problem and Need statements

1 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.

[pic]

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.

2 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.

3 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.

Design Alternatives

Contrail formation frequency heavily depends on the weather and humidity in the cruising altitude (troposphere 10-12 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.

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Figure 6: Five alternatives for flight path design

1 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 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.

2 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.

3 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.

[pic]

Figure 7: Vertical maneuvering for ISSR avoidance

4 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.

[pic]

Figure 8: Horizontal maneuvering for ISSR avoidance

5 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).

6 Value Hierarchy

The utility of each alternative route will be studied with the following values in mind:

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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.

Method of analysis

1 Simulation

The following diagram shows the various inputs and outputs to and from the simulation.

[pic]

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. This allows the system to be scaled up to test large numbers of aircraft.

2 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.

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.

Results

TBD

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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