Perceptions of emission reduction potential in air transport: a structural equation modeling approach

Abstract

This study employs a structural equation modeling (SEM) approach to identify the key perceptions that influence greenhouse gas (GHG) emission reduction potential (ERP) in air transport. It explores the correlation relationships between various perceptions and air transport GHG emission reduction potential. Personal approach and self-administered surveys were used to collect data from 249 aviation experts. The results of the SEM showed aircraft technology and design, aviation operations and infrastructure, socioeconomic and political measures, and alternative fuels and fuel properties are the key influencing perceptions for reducing GHG emissions. Aircraft technology and design had the strongest ERP, followed by aviation operations and infrastructure with a strong correlation between them. The structural model proved reliable and in agreement to identify the perceptions of the ERP. The outputs can be used to measure the level of knowledge and understanding about the ERP of air transport and can provide airlines with valuable information for designing appropriate air transport policies for emission reduction.

Appendices

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Appendix 2: Explanation of the ERP decision variables

S. no.	Decision variable	Explanation
1	Aircraft maximum takeoff weight (PATDA)	Maximum takeoff weight of an aircraft is a value defined by the aircraft manufacturer. It is the maximum mass at which the aircraft is certified for takeoff due to structural or other limits. Aircraft maximum takeoff is the most important factor in fuel economy, because more lift-generating drag results as weight increases. If the weight is reduced, engines that are smaller and lighter can be used, and for a given range the fuel capacity can be reduced. Thus, some weight savings can be compounded for reduction of aviation CO2 emission, which is proportional to fuel burn
2	Aircraft structural weight (PATDB)	Includes the weight of the structure, power plant, furnishings, installations, systems, and other equipment that are considered an integral part of an aircraft before additional operator items are added for operation. The performance of an aircraft is connected with fuel burn since a more fuel-efficient aircraft needs less volume to store the fuel, reducing the structural weight of the airframe
3	Wing reference area (PATDC)	It is the trapezoidal portion of the wing projected into the centerline. It is evaluated when the wing loading is selected. As the wing area is increased, both lift produced and wing weight are proportionally increased
4	Composite material use (PATDD)	Means how much  % of composite material is being used for aircraft wing, fuselage, and tails. For example, a technology which utilizes light-weight composites for the construction of the aircraft may lower airframe weight by 20 %. Thus, the technology is represented by a k-factor of 0.8 which is applied to the aircraft’s airframe weight, resulting in a lower aircraft gross weight. Since the aircraft weight has dropped, less fuel is required, further reducing the weight of the aircraft beyond the initial 20 % reduction.
5	Lift/drag ratio (PATDE)	In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing, divided by the aerodynamic drag it creates by moving through the air. A higher or more favorable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft’s required lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy, climb performance.
6	Thrust-specific fuel consumption (PATDF)	This is the mass of fuel needed to provide the net thrust for a given period, e.g., lb/(h. lbf) (pounds of fuel per hour pound of thrust) or g/(s. kN) (grams of fuel per second-kilonewton)
7	Engine bypass ratio (PATDG)	The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rates of air drawn through the fan disk that bypasses the engine core (un-combusted air) to the mass flow rate passing through the engine core.
8	Aircraft range (PAOIA)	This is the total distance that an aircraft can fly with full fuel tank and without refueling. This consists of takeoff, climb, cruise, descent, and landing
9	Aircraft fuel weight (PAOIB)	The required amount of the total fuel weight necessary for a complete flight operation depends upon the mission to be followed, the aerodynamic characteristics of the aircraft, and the engine-specific fuel consumption. Additional weight is introduced if an aircraft takes more fuel onboard than that required by the fuel flight plan.
10	Payload (PAOIC)	The load available as passengers, baggage, freight, etc., after the weight of pilot, crew, usable fuel have been deducted from the useful load.
11	Numbers of seats (PAOID)	Number of Seats is the total number of seats to be arranged as described in the airplane
12	Cruise speed (PAOIE)	The speed of an aircraft during cruise mission segment. The cruise speed for an aircraft, usually somewhat below maximum, that is comfortable and economical. A reduced cruise speed has previously been considered as a means for reducing mission fuel burn. One drawback of the reduced speed is a negative impact on airline productivity and passenger acceptance, especially for long-range missions. For short- to medium-range aircraft, however, the flight time increase is less problematic, thus making slower cruise an attractive possibility
13	Crew weight (PAOIF)	It is the weight of the people who are responsible to conduct the flight operations and serving passengers and payload
14	Terminal efficiency (PAOIG)	To isolate the impact of airport-specific differences in terminal efficiency, we include the variables for airport origins and destinations. Airport arrival and departure procedures consume considerable fuel, and we hypothesize that some airports are more fuel efficient than others in this respect. As the airports may require aircraft to meet certain arrival fixes that may be at nonoptimal altitudes or require nonoptimal speed profiles. The volume of operations and congestion at hub airports has been found to cause a great deal of inefficiency during departure and arrival operations
15	Social demand (PSEPA)	Aircraft fuel economy, which is a surrogate measure of jet engine emissions (mostly CO2). Currently, the social for demand fuel-efficient and low-emission aircraft is not strong enough because the general public is not well aware of the effects of aviation emissions on the global climate
16	Fuel cost (PSEPB)	The fuel cost is the main driver for improvements to aircraft fuel efficiency. When oil prices soar, airlines actively adopt advanced aircraft with greatly improved fuel economy
17	Voluntary measures (PSEPC)	Serving or acting in a specified function of one’s own accord and without compulsion or promise of remuneration
18	Demand shift (PSEPD)	Account for changes in travelers’ mode choice behavior or reduction of demand due to nontravel alternatives (e.g., video-conferencing and virtual meetings)
19	Charging carbon emission (PSEPE)	An alternative economic measure to reduce emissions of CO2 by commercial air transportation could be to apply a system of social cost of carbon as developed by the US EPA (Environmental Protection Agency). Generally speaking, the system is based on estimating the monetary value of social/economic damages or the value of avoiding these damages associated with the marginal increase or decrease, respectively, in CO2 emissions. For kerosene-fueled aircraft, CO2 emission is directly proportional to fuel burn
20	Alternative fuel type (PAFPA)	Selection of suitable alternative fuel, which will reduce the fuel consumption from air transport
21	Net calorific value (PAFPB)	Net calorific value of a fuel portion is defined as the amount of heat evolved when a unit weight of the fuel is completely burnt and water vapor leaves with the combustion products without being condensed. One of the most important requirements of aviation fuel is high heat content for maximum range or payload
22	Energy density (PAFPC)	This is the amount of energy stored in a given system or region of space per unit volume or mass. Aircraft is rated at maximum takeoff weight (MTOW), which includes the weight of fuel, passengers, and cargo. If an aircraft reaches MTOW before its fuel tanks are full, fuel with a higher energy density will allow more passengers and cargo on a given route or will carry the same passenger and cargo load a longer distance. Volumetric energy content is also important as this affects the flight range available with a full load of fuel, especially in smaller aircraft and military aircraft
23	Aromatic content (PAFPD)	Aviation fuel containing one or more molecular ring structures having properties of stability and reactivity characteristic of benzene. One of the biggest concerns of alternative fuels has come from their low aromatic content. Fuels with high aromatics content, and especially fuels with high naphthalenes content, form more of these carbonaceous particles. Since these carbonaceous particles are potentially harmful, both the total aromatic content and the total naphthalenes content of jet fuel are controlled
24	Carbon content (PAFPE)	Carbon particles that are not completely consumed are responsible for the visible smoke that some engines emit. Smoke formation is determined mainly by engine design and operating conditions, although for a given design, fuel composition can influence emissions. Better mixing of fuel and air results in more complete combustion and, thus, the less carbon formation
25	Thermal stability (PAFPF)	Thermal stability is one of the most important jet fuel properties because the fuel serves as a heat exchange medium in the engine and airframe. Jet fuel is used to remove heat from engine oil, hydraulic fluid, and air-conditioning equipment. Fuels with poor thermal stability will leave deposits in the engine fuel system which will degrade performance and require more frequent maintenance. This is a very demanding requirement for jet fuel and may become even more so in the future
26	Flash point (PAFPG)	The flash point is the lowest temperature at which the vapors above a flammable liquid will ignite on the application of an ignition source. At the flash point temperature, just enough liquid has vaporized to bring the vapor air space over the liquid above the lower flammability limit. The flash point is a function of the specific test conditions under which it is measured. The flash point of wide-cut jet fuel is below 0 °C (32 °F) and is not typically measured or controlled
27	ERPA	Emission reduction potential measuring instrument

Appendix 3: Questionnaire

3.1 A Covering Letter

Dear Respondent,

This survey is being carried out as part of my research work at NIT Hamirpur to understand the emission reduction potential in the air transport and to identify the perceptions affecting aviation emission. Please answer the questions freely. You cannot be identified from the information you provide. I ensure the confidentiality of your response. Also, you should have at least about 5 years of experience related to the aviation field to participate in the survey.

The questionnaire should take about 20–25 min to complete. Please answer the questions in the space provided. Also, do not spend too long on any question. Your first thoughts are usually your best!

Even if you feel the items covered may not apply to you, please do not ignore them. Your answers are essential in building an accurate picture of the issues that are important to identify perceptions of emission reduction potential in the air transport.

I hope you find completing the questionnaire enjoyable, and thank you for taking the time to help. If you have any queries or would like further information about this research, please contact me: er.vedu@gmail.com.

Thank you for your cooperation

Vedant Singh,

PhD., Research Scholar,

Mech. Engg., NIT Hamirpur (H.P.)

INDIA-177005

Thank you.