Improvements in aircraft fuel efficiency have stagnated over past two decades, reveals new study
Mon 30 Nov 2009 – According to a comprehensive analysis by the International Council on Clean Transportation (ICCT), advancements in the efficiency of commercial aircraft have largely stood still in the last two decades, contrary to the strides made during the previous thirty years. The researchers say that without an effective carbon dioxide emission standard that covers aircraft types currently in production as well as newly-introduced lines, fuel prices alone are unlikely to spur large improvements. During the study, more than 25,000 planes produced and delivered over the past 50 years were analyzed. The authors suggest that contrary to conventional wisdom, the efficiency of new commercial jet aircraft does not improve continuously.
The ICCT researchers simulated fuel burn for full loads over design-range routes and calculated on the basis of both seat-kilometres (i.e. passengers alone) and ton-kilometres (passengers plus cargo).
The analysis found that fuel efficiency increased 80% from 1960 through to the end of the 1980s, with most of the progress coming during the arrival of widebody aircraft in the late 1960s, and with the development in the 1980s of more efficient mid-range aircraft such as the Boeing 757 and 767.
Through till 1990, the researchers estimate that the efficiency of new aircraft improved 2.1% and 2.0% annually on a seat-km and ton-km basis, respectively. During the 1990s however, efficiency gains dropped to less than 1% annually. After 2000, fuel efficiency did not improve at all on a per passenger basis, even as fuel costs rose dramatically from about 10% of operating expenses in 2004 to peak at more than one-third in 2008.
Further work is needed to understand these trends, they say, but offer some initial observations about likely drivers. In historical terms jet fuel was relatively cheap from 1987 until 2004, as measured in terms of its share of overall operating costs for major US airlines. Since aircraft manufacturers compete not only on fuel efficiency but also on cost, performance and reliability, it is perhaps not surprising, states the study, that during periods of cheap fuel the efficiency of new aircraft stagnates.
Second, the falling rate of efficiency improvement for new aircraft is also correlated with a two-decade dearth of new aircraft and engine designs, which translates to a noticeable increase in the production line age for today’s major commercial aircraft manufacturers.
The final likely driver, which ICCT will follow up in a future study, suggests that aircraft manufacturers reacted to low fuel prices by devoting an increasing share of component efficiency improvements to boosting the performance of passenger aircraft instead of reducing fuel burn and emissions.
“Conventional wisdom holds that fuel prices drive constant improvements in new aircraft efficiency but this analysis suggests efficiency improvements actually tend to come with the introduction of new designs, which are much less common today,” said ICCT senior researcher Daniel Rutherford, who co-authored the study with researcher Mazyar Zeinali.
Over the past year, there have been growing calls for fuel efficiency or CO2 standards for new aircraft from both regulators and the airline industry. This received fresh impetus with the agreement of ICAO Member States in October to endorse a global annual average fuel efficiency improvement of 2% per annum for the industry as the major plank of ICAO’s overall strategy for reducing international aviation CO2 emissions. ICAO is due to present its plans for a CO2 emissions standard for new aircraft types at the forthcoming Copenhagen climate change summit.
However, argue the researchers, applying a carbon dioxide standard only to new production lines could actually prove counter-productive as it may encourage manufacturers to delay the introduction of more efficient designs in favour of older, unregulated models. To avoid such an outcome, they conclude that a standard covering aircraft from both new and existing lines would be more effective.
San Francisco-based ICCT – whose goal “is to dramatically improve the environmental performance andefficiency of personal, public and goods transportation in order toprotect and improve public health, the environment, and quality oflife” – is an NGO observer to the technical and emissions working group under ICAO’s environmental committee (CAEP).
The study, ‘Efficiency Trends for New Commercial Jet Aircraft 1960-2008’, can be downloaded from the ICCT website.