|Fig. 1: Airbus A320neo in flight. This aircraft burns 15 percent less fuel than the older A320 models.  (Source: Wikimedia Commons)|
Commercial air transport is crucial in our globalizing society and continually expands and connects networks across the world. The number of commercial aircraft passengers has continually increased since the development of aircrafts. Using the average density of jet fuel at 15°C and the fact that 85 billion gallons of jet fuel was consumed by the commercial airline industry in 2016, the calculated mass of jet fuel is approximately 259 million tonnes. [1,2] As of 2014, commercial aircraft contribute more than 700 tonnes of (CO2) into the atmosphere each year, which is approximated by the amount of fuel usage and stoichiometric conversions.  With commercial air travel becoming such a prominent form of transportation over the past several decades, investigating improvements for passenger aircraft efficiency are significant in lowering CO2 emissions into the atmosphere and fossil fuel consumption.
According to historic trends in measurements of aircraft fuel usage per seat, modern aircraft are approximately 80% more fuel efficient than aircraft of the 1960s through a combination of increased passenger capacity and technological improvements to improve fuel usage.  The rate of fuel efficiency improvement was quite variable throughout the past half century due to different developments in turbo engines, fuel consumption, and aircraft design. Between the 1960s and 1980s, the rate of fuel efficiency increased by an average of 3% annually, as determined by the International Civil Aviation Organization's calculated metrics, while there was essentially no increased fuel efficiency between the 1970s and 2000s.  However, as a result of recent fluctuations in fuel prices and the fact that fuel expenses comprise a significant amount of an aircraft's operating expenses, engineers have been working on improving aircraft fuel efficiency.  Furthermore, aircraft are incredibly energy efficient vehicles once they are up in the air. In fact, the faster the aircraft are able to travel, the more efficient they become. Since aircraft travel long distances and carry a limited quantity of fuel before needing to be replenished, engineers are working on improving the fuel efficiency of aircraft in order to fly longer distances with reduced amounts of fuel. The Airbus 320neo, shown in Fig. 1, is one of the most recent aircraft developed. It claims a reduction in fuel usage of approximately 15 percent compared to previous the previous Airbus 320 model.  The "neo" in the new aircraft's name refers to the use of a new, more fuel-efficient engine, demonstrating an example of the relationship between technology and efficiency improvements.
One of the many methods in improving aircraft efficiency is optimizing the wing designs. Boeing, one of the largest commercial aircraft manufacturers, and the National Aeronautics and Space Administration (NASA) have been collaborating on a new aircraft wing design that makes aircraft wings longer, thinner, and lighter.  Since the weight of an aircraft directly increases the amount of fuel, CO2 emissions, and money spent on flying the aircraft, the new wing design could significantly increase the efficiency of commercial aviation. The researchers developing the new aircraft wing design propose that both fuel consumption and CO2 emissions would be reduced compared to current commercial aircraft. 
Another less technological advancement to improve aircraft efficiency would be to optimize airspace usage across various geopolitical borders. Using Europe as an example, aircraft currently have to navigate across 40 different flight control zones, along with avoiding military and temporary no-fly zones.  The large number of flight control zones and restricted airspaces cause many commercial aircraft to follow very indirect paths while traveling from one destination to another. Fortunately, there is currently a proposal for the flight control zones to merge to become a single European sky, allowing aircraft to fly in the most efficient path possible without the challenges of traversing multiple airspaces, decreasing fuel consumption. 
As the world continues to develop and globalization spreads, commercial aircraft have become increasingly important to transport people and cargo across long distances. In the next 20 years, the amount of aircraft in service is expected to double, meaning the amount of fuel consumption will double as well.  Although commercial aircraft have come a long way in terms of efficiency since the 1960s, the demand for increasingly efficient aircraft will persist. Further advancements in all aspects of aircraft development are needed to continue making commercial air travel more efficient and sustainable for decades to come.
© Davis Chhoa. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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