7.6 Historical Trend in Aircraft Fuel Efficiency

Marcos Antonio de Lima Filho, PhD.

The evolution of the aviation industry has been characterised by a continuing quest for fuel efficiency. Technological advancements, including the advent of lighter materials, superior engine performance, and aerodynamic refinement, have contributed to a reduction in fuel consumption by over 70% since the start of the jet age (IATA, 2019a). Operational strategies, like optimal flight paths and altitudes, load factors, and cabin layout also play a significant role in determining efficiency.

In aviation, where thousands of flights take off and land every day, and millions of meals are served to passengers annually, even minor enhancements can result in significant long-term cost savings. Qantas, for instance, claims to have reduced its annual fuel consumption by 535,000 kg merely by introducing glassware, plates, cutlery, linen, and trolley carts that were 11% lighter on its international flights. This illuminates how interior aircraft design can affect fuel efficiency more than people might realise. The introduction of lighter materials in new or retrofitted aircraft — including their seats, lavatories, stowage bins, lighting, ceilings, interior lining, and insulation — can lead to solid fuel savings. Some airlines are even considering eliminating entertainment systems altogether, given the widespread use of smartphones and tablets, which would further reduce weight and fuel consumption.

Given its vast array of determinants, fuel consumption indeed serves as a comprehensive indicator of aircraft evolution. This measure combines the impact of all sorts of innovations, ranging from minor onboard equipment modifications to major technological leaps in turbofan engines and overall aircraft design.

The advancement of fuel efficiency in the aviation sector has been the subject of extensive research by academic scholars, governmental bodies, industry organisations, and environmental advocates alike. The overarching theme of these studies affirms a trend towards increased aircraft efficiency, despite the variability in the reported magnitudes of fuel burn reductions (Table 7.6.1).

This research modelled the average energy consumption (as litres of aviation fuel) per seat of newly delivered passenger aircraft. Figure 7.6.1 shows that aircraft entering service in 2020 are 79% more efficient than the first-ever commercial jet, the de Havilland Comet, introduced in 1953.

As an early pioneer of jet propulsion, the Comet was unusually inefficient. This inefficiency was largely due to the Comet’s high fuel burn rate coupled with a relatively small passenger capacity. These two factors together established a high baseline for efficiency metrics, contributing to a subsequently inflated rate of reduction. As a result, some researchers propose the exclusion of these early models from comparative analyses to counterbalance their outsized impact on efficiency metrics (e.g., Peeters et al., 2005; Rutherford & Zeinali, 2009). By recalibrating the baseline of this study to omit the early jets of the 1950s and 1960s, the overall reduction in fuel consumption shifts from 79% to 63%.

Regardless, I believe in the importance of situating these efficiency measures within their historical context. The jet age was still in its nascent stages during the 1950s and early 1960s, and the pioneering aircraft of this era, like the Comet, were understandably not as refined or efficient as their modern counterparts. Dismissing these early advancements undermines the iterative and exploratory nature of emerging technologies. Hence, these milestones in aviation history should not be forgotten.

Figure 7.6.1 shows that some decades experienced greater fuel efficiency improvements than others. In the 1980s, the average fuel burn per seat dropped an average of 5.7% each year. This decade is marked by the rapid adoption of new technologies and efficient aircraft design principles, such as high-bypass turbofans and improved aerodynamics. The 1980s were followed by two decades of marginal improvements at a compounded annual reduction rate of less than 1%.

The past decade (2010–2019) has seen a quickening of fuel burn reductions thanks to the introduction of many new fuel-efficient models, including the Airbus A320neo, Boeing 737 MAX, Airbus A350, and Boeing 787 families (Zheng & Rutherford, 2020). According to manufacturers, these new models are 15% to 25% more fuel efficient than their predecessors (IATA, 2019a). However, considering that the 777X is the only known new aircraft model on the horizon, the decline in fuel consumption may slow down again in the upcoming decade.

This historical progress has been observed by numerous academic scholars (Lee et al., 2001; Thomas et al., 2008), governmental bodies (Peeters et al, 2005; European Union Aviation Safety Agency, EASA, 2019), industrial entities (IATA, 2019b), and environmental organisations (Rutherford & Zeinali, 2009; Kharina & Rutherford, 2015; Zheng & Rutherford, 2020).

However, these studies have yielded varying figures and somewhat inconsistent results, with even the same research team (such as the ICCT) producing different outcomes. Unfortunately, a major limitation of these studies (including the current thesis) is that “the data is not gained from the actual airlines and is therefore a patchwork of assumptions” (ATAG, 2019). Instead of modelling fuel usage and passenger loads, the International Air Transport Association (IATA) used airline operational data on fuel efficiency performance (ATAG, 2021). Different modelling methodologies, data sources, and time spans may account for these disparate outcomes.

There is also much disagreement concerning efficiency metrics: The ICCT 2020 report utilised two measures (block fuel intensity and ICAO’s metric value), although in its 2015 and 2009 reports, it utilised fuel/passenger-km. Instead of fuel burn, IATA currently recommends a per-passenger CO2 emission calculation as a measure of the carbon footprint from flying activity. Another methodological concern worth considering is the impact of constant baseline recalibration. This practice, while sometimes necessary for eliminating anomalies, can undermine the recognition of recent improvements in fuel efficiency. By continuously shifting the point of reference, we risk 'erasing' past successes and diminishing the apparent magnitude of progression in this domain.