Fuel efficiency development and prediction
Climate impact pressures are increasingly driving the need for a better picture of what the future may hold for aviation. Several demand scenarios exist (principally those of the UN International Panel on Climate Change), but these need second tier interpretation to
account for technology, operational and market options for change. An understanding of the relative emissions efficiency gains from different areas of performance is crucial to industry and governmental decision making.
Aircraft efficiency (e.g. emissions / passenger km) depends upon engine and airframe issues such as structures, propulsion and aerodynamics as well as load factors, routing efficiencies, air traffic management, airline operational models (eg hub and spoke versus point to point) and economies of scale.
This study will explore the extent to which technology and operational factors may contribute to improvements in overall fuel efficiency. It will unpack past performance on fuel efficiency by looking at inventories and historical data to determine the trends for each element of cumulative efficiency improvement. It will try to identify the drivers behind historical trends and examine if a detailed understanding of past performance can help to guide future developments. The work will engage various stakeholders both to obtain data and to inform study concepts.
The study work will lead to the development of a proposal for a ‘what if’ model – the Integrated Fleet Assessment Tool. This would estimate the fuel efficiency of the fleet by linking available models and testing various assumptions on efficiency change.
In this study the efficiency of the collective fleet in airline service is assessed on a global basis. Efficiency improvements considered in this study can be derived from aircraft engine specific fuel combustion (SFC) characteristic, airframe improvements and also from operational improvements and the most appropriate metric is the aircraft system fuel or traffic efficiency i.e. fuel used per available seat or revenue passenger kilometre. Analysis of global fuel and aviation statistics has provided trends in overall aircraft system fuel efficiency from 1970 to 2006.
These trends in fuel efficiency calculated in this study confirm a 60% improvement in fuel efficiency since the early seventies to today’s fleet as mass of fuel per ASK. However a great part of this improvement was achieved during the 1970s (a 43% improvement is shown between 1971 and 1981). Further improvements over the last 25 years have been much more modest and fuel efficiency (as kg fuel per ASK) has fallen from 4.7 kg-fuel per ASK in 1981 to 3.3 kg-fuel per ASK in 2006 (approximately a 28% improvement). Estimation of the source of fuel efficiency improvements has shown a 70% improvement in fuel efficiency as fuel per RPK between 1970 and 2006 can be broken down into improvements due to load factor (20%), aircraft size (26%) and finally technical and operational improvements to the fleet (24%).
Looking at the most recent 6-year period analysed (2000 to 2006), the improvements in fuel-economy mean that 15% less aviation fuel was used (and therefore emissions of CO2) than would have been used without changes in efficiency. Over this 6-year period increases in load factor mean that a saving of 6% was made (1.1% per annum); there was no significant difference in average aircraft size; and a 9% saving was made by changes in fuel burnt per aircraft kilometre i.e. fuel per ASK (1.4% per annum).
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