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Green Aviation: A mission towards a clearer sky
Ts. Siva Pragathesewaran

11-MAY-2025

Introduction

Sustainability is derived from the word 'to sustain', which refers to the general environmental, social, and economic impact. The committee on Aviation Environmental Protection (CAEP), the ICAO council's technical committee, was established in 1983. The Council formulates new policies and adopts new standards for sustainable aviation. Malaysia is one of the observer countries committed to the organization's goal. CAEP's 'Working Group 4' - CORSIA (The Carbon Offsetting and Reduction Scheme for International Aviation) was introduced in 2016 to meet the 2020 baseline comparison of carbon-neutral growth in the Aviation Industry. However, due to the COVID-19 pandemic, the baseline was adjusted to be equivalent to 2014. Phase 1 is between 2021 to 2023. Phase 2 will kick off from 2024 to 2026. The goal is to achieve 50% of 2005's emissions by 2050 [1]. This goal depends on three prime factors: technological advancements, operational improvements, and the introduction of sustainable aviation fuel (SAF).

Fossil fuel - the burning problem

The types of fuel that are used to power aircraft engines at present are called fossil fuels. It is derived from the Latin word meaning "obtained by digging". As the name suggests, extracting fossil fuel involves drilling deep into the Earth's crust. Since the compound is organic, it is naturally loaded with carbon. Jet A-1, Jet A, Jet B, JP-8 and AVGAS are commonly used fuels. However, it is not the fact that it is organic that causes the problem. The chemical compound in the fuel and the burning process present the problem.

The diagram depicts combustion byproducts in a typical Turbofan engine.

• Greenhouse gases (GHG) – Mainly made up of carbon dioxide and water vapour. These GHGS efficiently absorb the infrared radiation from the atmosphere, transmitting some of it to the Earth. The levels of the GHGS are exponentially high, and they heat the Earth's surface, thus increasing its temperature. This is known as global warming. The effect of global warming is known as climate change.

• Products of incomplete combustion – These are known as Unburnt Hydrocarbons (UHC). The main gas is carbon monoxide (CO), a poisonous gas mainly produced during low Engine power or idle settings.

• Oxides of Nitrogen (NOx) – another type of GHG that has a similar effect to CO2. This gas is mainly produced in higher engine power settings.

• Particulate Matter (PM) – the exhaust's volatile gases that adversely affect the environment.

The 3 Prime Factors

1. Technological advancements

Advancements in technology, especially in commercial aircraft, have played the most vital role in shaping the new era of aviation. From 2000 to 2019, approximately 38.9 million flights were recorded yearly (pre-COVID-19 levels). However, due to the coronavirus pandemic, flights dropped to 16.4 million in 2020. These figures are set to rise as more and more aircraft are inducted into service. Large airlines shed their older planes for newer, more fuel-efficient ones. These older planes end up in aircraft junkyards, or some other airlines would buy them for considerably cheaper rates. The technological leaps are both in the design of the airframe and the propulsion system. Some critical design changes are:

(a) Fully composite Airframe – Lightweight fiber

The Beech Starship I (in the early 1980s) was the first all-composite aeroplane to obtain FAA certification. The regulatory requirements set the standard for composite structures today. Taking the lead from Beech, in the 1980s, Boeing 737 utilized a composite sandwich for its horizontal stabilizer. The Airbus A320 later followed this. As the saying goes, 'necessity is the mother of inventions; the rising fuel cost was the catalyst that created the impetus for using composite materials in aviation.

The Boeing 787 Dreamliner entered service in 2011. The fundamental design changes are the extensive use of carbon composite materials such as CFRP – Carbon Fiber Reinforced Plastic, Carbon sandwich and Fiberglass sandwich on the fuselage, flight controls and nacelles, the No-bleed Engines, high voltage DC power (HVDC) and solid-state remote power distributors (RPDUs - replacing the traditional contactors and relays). Together, they contribute to total fuel savings of between 20 and 30 percent. The Chevron nozzle of the exhaust reduces the Noise signature by 60 percent. Similarly, the ultra-modern Airbus A350 utilizes up to 53 percent of composite materials.

(b) Ultra-High Bypass turbofan engines (UHB) and Geared Turbofan (GTF)

In service since 2014 (GTF‐1000 by P&W), it is a technology demonstrator for ultra‐high bypass (UHB) turbofan engines designed with bypass ratios over 12. The GTF optimizes the fan and core operation, allowing a reasonable engine and core size. The fan drive gear system prevents the Fan tip speed from exceeding the speed of sound (Mach 1), thus eliminating the high-pitched noise.

The combination of UHB and GTF reduces the Effective Perceived Noise in Decibels (EPNDb) up to 25, Low-Temperature Oxidation (LTO) NOx by 75%, and fuel burn by up to 25%.

(c) Electric propulsion (EP) system

This concept has been a dream for futurists for many decades, limited only by the available technology. The significant advancements in the field of electric cells, such as Lithium-ion (Li-ion), Lithium-Sulphur and hydrogen fuel cells, seem promising. The principle of EP is where electricity is used to increase the exhaust velocity. In a jet engine, electricity is used to turn the high-pressure compressors (HPC), which drive the turbines. The amount of electricity required is simply enormous. Also, the development cost and stringent regulatory requirements hamper progress.

Combustion engines have thousands of moving parts, and their efficiency reduces at higher altitudes. The cost of routine maintenance is also significantly increased, which accounts for the operating cost. EPs, in contrast, do not experience efficiency loss at higher altitudes and require less maintenance. However, liquid jet fuel has a fantastic energy density that no EPs match. MagniX, for example, is building a family of EP systems for commercial aviation, assuring more than 93 percent motor efficiency. Norway has mandated that all its domestic flights be Electric by 2040. Unless the state takes a serious undertaking, implementation and change will be slow.

2. Operational Improvements

This is the most common approach currently being adopted by airlines worldwide to meet the efficiency and cost of burning jet fuel.

(a) Weight reduction

From removing accessories such as footrests, heavy photo frames, and exclusive granite countertops and optimizing the potable water uplift, the list is too long for an airline to do potentially. Another area is the implementation of Electronic Flight Bags (EFBs) and Electronic Technical Logs to replace the bulk of papers that are usually kept in the flight deck. The manual updates are done seamlessly by the Terminal Wireless system, which reduces the need for rigorous manual inputs, which are always time-consuming.

(b) Advanced Air Traffic Management

Air transport consists of three essential elements: the aircraft, airspace, airport infrastructure, and air traffic management system (ATM). Advanced ATMs aim to optimize the trajectory and flight regime operations to optimize fuel consumption. The components of the ATM include:

• Flight Management System or FMS – Introducing Fly by Wire technology and Fly by Light (fibre optics) enabled high-speed data flow between the FMS and the aircraft systems. The closed-loop feedback signals from the control surfaces allow a more efficient long-range cruise with less drag, translating to less fuel burn.

• Required Navigation Precision (RNP) – This new electronic Performance Based Navigation (PBN) system must operate in certain airspace blocks where ATC radar monitoring is unavailable. RNP-capable aircraft can calculate their position within a circle radius of x nautical miles and have an accuracy of almost 95% of Total System Error (TSE). For example, RNP 10 is required for oceanic and remote areas with limited external navigation. With its associated RNAV, RNP significantly improves the accuracy and performance of aircraft operations. The result is excellent energy efficiency.

(c) Sustainable Aviation Fuel (SAF)

One of the pillars of sustainability is renewable energy sources, which currently have a market share of 5 % and are projected to be 10% by 2030. SAFs do not contain hydrocarbons or sulphur, thus reducing the soot and particulate matter as byproducts of combustion. This causes fewer ice crystals to form at higher altitudes. There are three generations of biofuel:

First Gen – food crops, vegetable oil, soybeans. Readily available.

Second Gen – Non-food sources – Algae, jatropha, halophytes. More complex and costly. More sustainable and reduces GHG more than the First Gen.

Third Gen – Bio-engineered bacteria, algae, hydrogen from biomass or synthetic methane. Still under R&D and the most promising area.

Hydrogen (H2) is considered one of the best alternatives for a clean, sustainable energy source. The calorific value of H2 is higher than that of coal, ethanol and petroleum. The byproduct is water (H2O), which is not harmful to the environment. Currently, hydrogen production through electrolysis requires electrolytes, which are pretty costly. In this process, much energy is needed to produce hydrogen. The hydrogen is then used to generate the power. Some researchers have attempted to use microbial electric cells (MEC) to produce hydrogen as a sustainable technique. The other challenge is in the storage of hydrogen. It is a lightweight gas with tiny molecules. In pressurized liquid form, it is known to leak through metal containers.

In early 2021, Rolls-Royce announced that it had its first tests on a 100% sustainable aviation fuel (SAF) suitable for business jets on its Pearl 700 and Trent 100 engines. Previously, a blend of 50% biofuel and jet fuel was the maximum permitted for Rolls-Royce Engines. The 100% unblended fuel could potentially reduce the CO2 net emissions by 75%, heralding a new era of green aviation.

Etihad Airways is one of the leading airlines actively engaged in aviation sustainability. The introduction of the Boeing 787-10 ecoDemonstrator (Greenliner) in 2020 further solidified its position as a leader and committed to achieving zero net carbon emissions by 2050. The ecoDemonstrator is a joint venture with Boeing, NASA and SAFRAN. In 2019, in collaboration with Masdar University, Etihad established the Sustainable Bioenergy Research Consortium (SBRC), utilising locally produced biofuel from the Salicornia plant. Etihad focuses on all aspects of sustainability, from optimizing flight routes and approaches to reducing landfill waste by eliminating single-use plastics, optimizing potable water usage, and implementing the electronic technical log.

Conclusion

The planet will surely be better if all airlines and operators take responsibility for achieving net-zero carbon emissions by 2050. The dream of a clean sky is never an individual effort. As the saying goes, "No man is an island." Similarly, only through deep collaboration can we achieve the real goal—together, we are stronger.

References:
[1] Offsetting CO2 Emissions with CORSIA, available at https://www.iata.org/en/programs/environment/corsia/ (2021)
[2] S. Farokhi, Future Propulsion Systems and Energy Sources in Sustainable Aviation. John Wiley & Sons, Ltd, 2019.
[3] C. Kassapoglou, 'Design and Analysis of Composite Structures: With Applications to Aerospace Structures'. https://www.researchgate.net/publication/350191295_Design_and_Analysis_of_Composite_Structures_With_Applications_to_Aerospace_Structures (accessed Jul. 11, 2022).
[4] C. Hughes, 'The Promise and Challenges of Ultra High Bypass Ratio Engine Technology and Integration', AIAA Aero Sci. Meet., pp. 0–11, 2011, Accessed: Jul. 11, 2022. [Online]. Available: www.nasa.gov.
[5] 'magniX'. https://magnix.aero/ (accessed Jul. 11, 2022).
[6] GE Step Ahead, available at: Required Navigation Performance programs around the world | GE Step Ahead, available at: moneycontrol.com (accessed 20 December 2021)
[7] Rolls-Royce trials 100% sustainable business jet aviation fuel - AviTrader Aviation News, https://www.avitrader.com/2021/02/02/rolls-royce-trials-100-sustainable-business-jet-aviation-fuel/ Accessed: 2022-07-11

[8] Etihad Inaugurates Pioneering 2020 ecoDemonstrator aircraft into servicehttps://www.etihad.com/en/news/etihad-inaugurates-pioneering-2020-ecodemonstrator-aircraft-into-service, Accessed: 2022-07-11