Efficiency Trends for New 

Commercial Jet Aircraft

1960 to 2008
ii Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008

www.theicct.org 

©November 2009 The International Council on Clean Transportation 

Design layout and format by Yulee Kim 

Printed on 100% recycled paper with soy-based ink 

The goal of the International Council on Clean Transportation (ICCT) 

is to dramatically improve the environmental performance and 

efficiency of personal, public and goods transportation in order to 

protect and improve public health, the environment, and quality of 

life. The Council is made up of leading regulators and experts from 

around the world that participate as individuals based on their 

experience with air quality and transportation issues. The ICCT 

promotes best practices and comprehensive solutions to improve 

vehicle emissions and efficiency, increase fuel quality and 

sustainability of alternative fuels, reduce pollution from the in-use 

fleet, and curtail emissions from international goods movement. 

Authors:

Daniel Rutherford, Ph.D.

Senior Researcher, International Council on Clean Transportation

Mazyar Zeinali, Ph.D.

Researcher, International Council on Clean Transportation

The authors would like to thank our many colleagues around the world that have 

generously contributed their time and insight in reviewing and commenting on 

the draft versions of this paper, including Steve Arrowsmith, Theo Rindlisbacher, 

Chris Eyers, Paul Peeters, Dimitri Simos, Tim Johnson, and Jos Dings. Our 

gratitude also goes to Paul Madden and Ian Waitz for kindly providing information 

on previous related studies, and to the members of CAEP WG3, to whom this 

work was originally submitted. We also thank our ICCT colleagues Drew Kodjak, 

Fanta Kamakate, Matt Crenson, John German, Andrew Jens, Ray Minjares, Ed 

Pike, and Kate Blumberg for their review and constructive comments.

Generous support for this work was provided by the William and Flora Hewlett 

Foundation and the ClimateWorks Foundation.
iii Abstract 

ABSTRACT

Concerns about aviation’s growing climate impact have revived interest in CO2

emission standards for new aircraft. To date, commercial aviation has been 

perceived to produce continuous improvements in efficiency by quickly adopting 

fuel-efficient technologies and designs as a natural response to fuel prices. This 

paper describes an historical analysis of sales- and activity-weighted fuel 

efficiency for new jet aircraft from 1960 to 2008 that suggests that fuel costs alone 

have not produced consistent improvements in aircraft efficiency. Key findings 

include:

• The average fuel efficiency of new passenger aircraft has 

approximately doubled on both a seat-km (passengers only) and tonkm (passengers + freight) basis since 1960, less than previous 

estimates. 

• New aircraft efficiency has improved substantially in only two of the 

last five decades, and stagnated in recent years. On average, fuel 

efficiency has remained flat on a seat-km basis and improved only 

0.29% annually on a ton-km basis since 2000. 

• Diminished efficiency gains are correlated with historically low fuel 

prices between 1987 and 2004 and a tripling in the average age of 

aircraft and engine manufacturer production lines since 1989. 

We conclude that fuel costs alone have not been sufficient to stimulate increased 

aircraft efficiency, and that improvements in fuel efficiency due to the introduction 

of new aircraft have decreased over time. These findings suggest that a CO2

standard that applies to newly built aircraft from current production lines, not just 

to new designs, is most likely to reduce emissions. 

ABSTRACT 1. AVERAGE FUEL BURN FOR NEW AIRCRAFT, 1960-2008

25!

50!

75!

100!

1960! 1965! 1970! 1975! 1980! 1985! 1990! 1995! 2000! 2005!

Fuel burn at design range (1960=100) !

Year!

ton-km

seat-km

08!

1960s!

1970s!

1980s!

1990s!

post-2000!

Annual Improvement 

 Period Seat-km Ton-km

 1960s 2.3% 3.6%

 1970s 0.6% -0.1%

 1980s 3.5% 2.5%

 1990s 0.7% 0.9%

 post-2000 0.0% 0.3%
 1 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008

1. INTRODUCTION

The need to constrain the rapid growth of 

aviation’s impact on the global climate 

is becoming increasingly clear. 

Since 1997, when Article 2.2 of 

the Kyoto Protocol requested 

that developed countries pursue 

the limitation and reduction of 

greenhouse gas emissions from 

aircraft through the International 

Civil Aviation Organization (ICAO), 

aviation’s contribution to global carbon 

dioxide (CO2) emissions has continued to 

grow. Global CO2 emissions from aircraft 

grew an estimated 45% between 1992 and 

2005. After accounting for their significant 

non-CO2 climate impacts, aircraft were 

responsible for an estimated 3.5% of 

historical anthropogenic radiative forcing 

(RF) in 2005 and 4.9% of total RF counting 

the probable effects of aircraft through 

aviation-induced cloudiness (Lee et al. 

2009). Moreover, ICAO recently forecast 

that global CO2 emissions from aviation will 

increase an additional 150% above 2006 

levels by 2036 (ICAO 2009a), a pace that 

would quadruple emissions by 2050. Given 

the lack of a global agreement on reducing 

international aviation emissions, studies 

suggest that aviation emissions threaten to 

erase the gains of developed countries that 

succeed in reducing emissions from other 

sectors (Bows et al. 2005). 

These facts have renewed calls for fuel 

efficiency or CO2 standards1 for new aircraft 

from a variety of stakeholders. In 2001, 

ICAO’s Committee on Aviation 

Environmental Protection (CAEP) concluded 

that a CO2 standard was unnecessary and 

potentially even counter-productive because 

fuel costs provided sufficient incentive for 

manufacturers and airlines to reduce actual 

CO2 emissions in operation (ICAO 2001). 

Since that time, the UK Department for 

Transport (DfT 2009) and US EPA (Federal 

Register 2008), among others, have 

expressed interest in an aviation emission 

standard. Boeing has also indicated its 

support for a CO2 standard for new aircraft 

designs (Carson 2009). ICAO has since 

reversed course and will present its plans for 

a CO2 standard for new aircraft types at the 

Copenhagen meeting of COP-15, where a 

post-Kyoto climate agreement will be 

discussed (ICAO 2009b). 

While a variety of technical issues need to be 

addressed in order to set a meaningful CO2

standard2, one key input into any standard 

will be to understand the natural historical 

rate of fuel efficiency improvement for 

aircraft. The aviation industry argues that 

the high cost of fuel motivates it to quickly 

adopt fuel-efficient technologies and 

practices. References to aviation, supported 

by industry analysis, typically allude to a 

“continual improvement” in fuel efficiency 

demonstrated by new equipment. A RollsRoyce analysis cited first in Albritten et al. 

(1997) and later in an influential IPCC report 

(Penner et al. 1999) estimated that the fuel 

burn3 of new jet aircraft had been reduced by 

70% between 1960 and 1997. Other studies, 

including Lee et al. (2001) and Peeters et al. 

(2005), have estimated relatively smaller 

reductions (approximately 64% and 55%, 

respectively) over similar timescales for new 

equipment. 

There are significant limitations to the 

studies described above. Each of these 

studies drew conclusions about historical 

trends using a relatively small number of 

aircraft, predominately or completely models 

flown on long-haul routes. Those studies 

also did not weigh the relative efficiency of 

individual aircraft models by sales or 

activity, a technique commonly used to 
2 Methods 

minimize outliers and to assure that the 

importance of the most commercially 

successful vehicle designs are accurately 

captured. As a result, the studies may not be 

representative of the broad historical trend 

for all new aircraft, particularly given the 

substantial contribution of narrowbody 

aircraft and regional jets to global fuel burn 

today. 

To inform current discussions of a CO2

standard for new aircraft, this paper presents 

an analysis of sales- and activity-weighted 

historical trends in new aircraft efficiency 

from 1960 to 2008. It aims to answer two 

simple questions: first, has the average 

efficiency of new aircraft improved 

continuously over time in response to fuel 

prices? Second, if progress has not been 

continuous, what factors other than fuel price 

seem to influence the rate of improvement? 

The following section describes our method 

of analysis. Section 3 describes the study’s 

key findings, while Section 4 briefly explores 

its policy implications. 

 

2. METHODS 

This analysis was conducted in three basic 

steps. First, representative aircraft were 

identified to cover the more than 27,000 new 

commercial jet aircraft sold worldwide since 

1952. Second, the fuel burn of those aircraft 

over characteristic missions was modelled 

using Piano-X4, an aircraft performance and 

emissions database. The Piano software 

suite has been used in ICAO policymaking 

and for the construction of several prominent 

aviation emissions models.5 Third, the fuel 

burn of representative aircraft was weighted 

by actual aircraft sales and estimated activity 

to create industry average efficiency trends 

for new aircraft. A detailed description of 

the methodology follows: readers new to 

this subject are encouraged to refer to the 

glossary in Appendix A as necessary. 

For this analysis, a data set of aircraft 

deliveries6 (month and year) by 

manufacturer, aircraft model/series, and 

engine model/series was purchased from Jet 

Information Services, publisher of the World 

Jet Inventory. The data set included 27,370 

individual aircraft delivered between 1952 

and 2008 seating 31 passengers or more. 

From this data set, 26,331 aircraft (96% of 

total) delivered by the ten largest commercial 

jet aircraft manufacturers (Boeing, Airbus, 

Douglas, Embraer, Bombardier, Fokker, BAE 

Systems, British Aircraft Corp, Aerospatiale, 

and Lockheed) between 1958 and 2008 were 

isolated. 

From this data set 704 distinct airframe/

engine combinations were extracted and 

matched to 96 representative aircraft in the 

Piano-X database, current to November 

2009. Representative Piano-X models were 

identified by matching aircraft model/series 

and engine model/series information 

provided by the developer of the Piano suite 

to the delivery dataset. Where multiple 

Piano-X aircraft models existed for a given 

aircraft/engine combination, representative 

models were assigned by using the most 

updated and highest maximum take off 

weight (MTOW) variants within Piano-X in 

order to assure that the most productive 

aircraft were being used. Since Piano-X was 

created to analyze current in-service aircraft, 

two Douglas DC-8 models (-53 and -55) 

were created by its developer to improve 

coverage of early deliveries in the dataset; 

additionally, the B737-200 was modified by 

the developer to make it more representative 

of early deliveries.7 Dedicated new freighters 

and military aircraft were removed, as were 

airframe/engine combinations for which no 

clear representative aircraft could be 
3 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008

identified within the Piano-X database (a 

total of 36 combinations, representing 698 

deliveries). Table 1 summarizes the Piano-X 

aircraft models used, which covered in total 

25,354 deliveries, or 93% of the initial 

delivery dataset.

Block fuel burn (fuel/available seat 

kilometer, or ASK, and fuel/available ton 

kilometer, or ATK) of aircraft delivered in 

each year was compared using Piano-X. 

Model default values were adopted for 

design weights, nominal seat counts, thrust, 

drag, and fuel flow. Aircraft were “flown” at 

full loads (all seats filled or maximum mass 

payload) over design range routes, including 

landing and take off, at available flight levels 

of 310 and 350 and at cruise speeds enabling 

99% specific air range. Fuel reserves and 

allowances were set at 370 km diversion 

distance, 30 minutes holding time, and 5% 

mission contingency fuel for all aircraft. Fuel 

burn per ATK was estimated through fuel 

burn with maximum payload (maximum zero 

fuel weight minus operating empty weight) 

at maximum range, while fuel burn per ASK 

was estimated at design range using 

Piano-X default values for the 

passenger to mass conversion. 

No additional allowance was 

made for belly freight for the 

ASK fuel burn estimation. 

The average fuel burn for new 

equipment (g fuel/ASK and g fuel/

ATK by year of delivery) by year was 

estimated by weighting the fuel burn of the 

96 representative aircraft by their sales and 

contribution to a year of fuel burn for aircraft 

delivered that year, normalized to 1960 for 

easy comparison to previous studies (1960 

FB = 100). Deliveries were classified as 

either widebody or narrowbody aircraft 

within the original Jet Information Services 

dataset: for further segmentation, 

narrowbody aircraft seating fewer than 100 

TABLE 1. PIANO-X REPRESENTATIVE MODELS USED

B707-320C B747-400 (875) Airbus A310-300 Douglas DC 8-53

B717-200 (v00) B747-400ER (910) Airbus A318-100 59t Douglas DC 8-55

B727-200A B747-SP (degrad) Airbus A318-100 68t Douglas DC 9-14

B737-200 B757-200 (220) p Airbus A319 basic Douglas DC 9-34

B737-300 (basic) B757-200 (255) p Airbus A319-100 64t Douglas DC 10-10

B737-400 (basic) B757-200 (220)r Airbus A319-100 75t Douglas DC 10-30

B737-500 (basic) B757-200 (255)r Airbus A320-200 77t Embraer 170 LR (v07)

B737-600 (NG basic) B757-300 (273)p Airbus 321-100 Embraer 190 LR (v07)

B737-600 (145) rev B757-300 (273)r Airbus A320-200 73t Embraer 190 AR (v07)

B737-700 (133) wglt B767-200 basic Airbus 321-200 89t Embraer 190 STD (v07)

B737-700 (NG basic) B767-200ER Airbus 321-200 93t Embraer EMB-135

B737-700 (154) wglt B767-300 Airbus A330-200 233t Embraer EMB-145

B737-BBJ1 B767-300ER Airbus A330-300 230t Canadair RJ 100

B737-700ER (158) wglt B767-400ER basic Airbus 340-200 275t Canadair CRJ 200ER

B737-800 (155) wglt B777-200 ER (IGW) Airbus 340-300E 276t Canadair CRJ 701

B737-800 (NG basic) B777-200 ER (max) Airbus A340-500 (v09) Canadair CRJ 900

B737-800 (174) wglt B777-200 LR (v04) Airbus 340-600 (v09) Fokker-F28 Mk4000

B737-BBJ2 B777-200 LR (max) Airbus A380-800 (v08h) Fokker F70 basic

B737-900 (NG option) B777-300 (660) Douglas MD-11 basic Fokker F100 basic

B737-900ER (187a) wglt B777-300 ER (v04) Douglas MD-81 Avro RJ-70

B747-100 (degrad) Airbus A300 600 light Douglas MD 82-88 Avro RJ 85 basic

B747-200B (833) Airbus A300 600R Douglas MD-83 auxCap Avro RJ-100

B747-300 (833) Airbus A300 B2-200 Douglas MD-87 Lockheed L-1011-200

B747-400-stretch (v91) Airbus A310-200 Douglas MD-90-30 Lockheed L-1011-500
passengers were classified as regional jets 

unless obvious derivatives of larger aircraft 

(e.g. 737-BBJs). Block hours flown were 

set at 2700, 2900, and 4200 hours per year 

for regional jets, narrowbodies, and 

widebodies, respectively, to reflect 

differences in the utilization across aircraft 

classes. As an example, fuel burn per ASK 

for aircraft delivered in a given year (y) was 

estimated via Equation 1.

The results of this analysis are summarized 

in Section 3. Simple sensitivity analyses of 

two key assumptions – the use of design 

range to estimate fuel burn performance, and 

the assumption of no incremental 

improvement within an aircraft-engine 

combination over its production lifetime – 

are presented in Appendix B. 

3. RESULTS AND DISCUSSION

The results of this analysis are summarized 

in Figure 1. The 51% reduction of fuel burn 

shown in that figure on both a seat-km 

(passengers only) and ton-km (passengers + 

cargo) basis translates to a more than 

doubling of the average efficiency of new 

aircraft between 1960 and 20088, an annual 

improvement of 1.5%. In contrast to 

conventional wisdom, efficiency has not 

improved continuously over time. 

Improvements were particularly rapid during 

the 1960s, peaking when widebody aircraft 

such as the 747 family came into wide 

 4 Results and Discussion 

!

FB(y) =

ni(y) " fi " [hi /ti]

i=1

96

#

ni(y) " si " ri " [hi /ti]

i=1

96

#

$

%

&

&

&

&

'

(

)

)

)

)

Where:

 FB(y) = fuel burn in year y (g fuel/ASK)

 i = Piano-X representative aircraft

 ni(y) = number of aircraft delivered in year y and 

 represented by i 

 fi = fuel burnt by aircraft i in design mission

 hi = annual block hours for aircraft i 

 ti = block time of design mission for aircraft i

 si = seats in aircraft i

 ri = design range of aircraft i

EQUATION 1. METHOD OF FUEL BURN WEIGHTING

25!

50!

75!

100!

1960! 1965! 1970! 1975! 1980! 1985! 1990! 1995! 2000! 2005!

Fuel burn at design range (1960=100) !

Year!

ton-km

seat-km

08!

1960s!

1970s!

1980s!

1990s!

post-2000!

Annual Improvement 

 Period Seat-km Ton-km

 1960s 2.3% 3.6%

 1970s 0.6% -0.1%

 1980s 3.5% 2.5%

 1990s 0.7% 0.9%

 post-2000 0.0% 0.3%

FIGURE 1. AVERAGE FUEL BURN FOR NEW AIRCRAFT, 1960-2008
production in 1970, and in the early to 

mid-1980s, when mid-range aircraft like 

Boeing’s 757 and 767 families powered by 

new high bypass ratio turbofans began to 

dominate production lines. At other times, 

such as during the 1970s and after 1990, 

efficiency has improved slowly or stagnated. 

The average fuel burn per ton-km for new 

deliveries actually increased during the 

1970s due to greater sales of narrowbody 

aircraft, which are designed to carry little 

belly freight and are therefore less efficient 

on a ton-km basis. 

 

The flattening slope of the fuel burn curves 

in Figure 1 suggests a notable decrease in the 

rate of fuel efficiency improvement over 

time, with an apparent inflection point 

around 1990 on a seat-km basis and 2000 on 

a ton-km basis. Through 1990, we estimate 

that the efficiency of new aircraft improved 

2.1% and 2.0% annually on a seat-km and 

ton-km basis, respectively. The annual 

improvement fell to only 0.75% (seat-km) 

and 0.88% (ton-km) during the 1990s. Since 

2000, the average efficiency of newly 

delivered aircraft has been flat on a seat-km 

basis and improved only 0.29% annually on a 

ton-km basis. Appendix C compares the 

results of this analysis with previous 

assessments of historical aircraft efficiency 

improvements, of which all save one 

(Thomas et al. 2008) show a similar fall-off 

in efficiency improvement over time. 

Further work is needed to understand these 

trends; however, some initial observations 

can be offered 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 (Figure 2, left axis). This 

correlates well to the period of modest 

efficiency improvement shown in the 

shadowed brown line (ASK line from Figure 

1, shown on the right axis of Figure 2) if one 

considers the amount of time needed to 

design, test, certify, and manufacture a 

modern jet aircraft. Since aircraft 

manufacturers compete not only on fuel 

efficiency but also on cost, performance, 

reliability, etc. (a point we return to below), 

it is perhaps not surprising that during 

periods of cheap fuel the efficiency of new 

 5 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008

40

50

60

70

80

0%!

10%!

20%!

30%!

40%!

 1971! 1975! 1979! 1983! 1987! 1991! 1995! 1999! 2003! 2007!

Seat-km Fuel Burn (1960=100)!

Fuel Cost % of Operating Expenses!

Year! Source: ATA, 2009.!

09!

FIGURE 2. FUEL COSTS AS A SHARE OF TOTAL OPERATING EXPENSES FOR US AIRLINES
 6 Results and Discussion 

aircraft stagnates. Figure 2 also shows the 

dramatic run-up in fuel prices after 2004, 

including the post-2007 spike and subsequent 

crash, the policy implications of which we 

will return to in Section 4. 

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 (Figure 3). As estimated by 

that graph, the average age of the production 

lines of today’s four major commercial jet 

manufacturers (Airbus, Boeing, Bombardier, 

and Embraer) has tripled since 1989. Since 

over the long-term most of the aggregate 

efficiency improvements for new equipment 

are expected to come from the 

commercialization of new, more efficient 

aircraft and engines, this trend helps explain 

the falling rate of improvement over time. 

Note as well the sharp reduction of average 

production line age during the early 1980s – 

a period of unusually fierce competition 

between manufacturers – and the 

corresponding period of rapid efficiency 

improvement shown on the right-hand axis. 

The final likely driver – introduced only 

briefly here and to be the subject of a future 

ICCT report – are notable improvements in 

the non-fuel burn related performance of new 

passenger aircraft, as measured by their 

design range, cruise speed, customer 

amenities offered, and cargo capacity. These 

improvements impose a fuel efficiency 

penalty, particularly on a seat-km basis, on 

passenger aircraft by boosting empty aircraft 

weight and drag during cruise.9 These trends 

suggest 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.10 Such a development would be 

consistent with Peeter et al.’s (2005) finding 

that other performance attributes, notably 

speed and range, were prioritized over fuel 

efficiency during the transition from pistondriven to jet aircraft during the late 1950s 

and early 1960s.

0!

20!

40!

60!

80!

100!

0!

5!

10!

15!

20!

25!

1960! 1965! 1970! 1975! 1980! 1985! 1990! 1995! 2000! 2005!

Seat-km Fuel Burn (1960=100)!

Age of Production Line (yr)!

Year !

Aircraft!

Series!

Engine !

Family!

08!

FIGURE 3. ESTIMATED AGE OF PRODUCTION LINE, 1960-2008
4. POLICY IMPLICATIONS 

Returning to the questions posed in Section 

1, this analysis suggests that, 

contrary to conventional 

wisdom, on average the 

efficiency of new 

commercial jet aircraft 

does not improve 

continuously: while 

efficient technologies 

and designs may be 

developed more or less 

continuously, their deployment is likely to be 

much more “clustered” and subject to market 

forces. When fuel prices remain low for an 

extended period of time, the incentive to 

market new aircraft and engine designs may 

weaken, and manufacturers may sacrifice 

fuel efficiency to increase other aircraft 

performance attributes. Since over the longterm the bulk of efficiency improvements 

from new equipment comes from new 

aircraft and engine designs rather than 

incremental improvements within a 

particular design’s production lifecycle, a 

lack of new designs directly contributes to 

stagnating new aircraft efficiency. 

This analysis shows that fuel price alone has

failed to continuously promote new aircraft 

efficiency since 1960; furthermore, the rate 

of improvement has flattened since 1990. 

The latter finding is likely due to historically 

low fuel prices between 1987 and 2004, 

although limits on the efficiency of current 

“tube and wing” airframe designs and 

interdependencies between fuel consumption, 

local air pollution, and noise may mean that 

the efficiency of new equipment is less 

influenced by fuel price now than it has been 

in the past (Royal Aeronautical Society 2005; 

Lee et al. 2009). It seems reasonable to 

assume that high fuel prices after 2004, 

should they continue, will impact the 

efficiency of not yet designed aircraft. Given 

that it now takes a decade or more for a new 

aircraft design to be brought to market, 

accurately predicting how large of an impact 

today’s fuel prices may have on new aircraft 

in the 2015 time frame will be important to 

setting a CO2 standard for new aircraft that 

provides real, additional emission reductions.

Worryingly, the slow pace of improvement 

since 1990 suggests that short-to-medium 

term efficiency gains from the introduction 

of new equipment may be quite limited. As a 

first approximation, fleetwide efficiency 

tracks the efficiency of new equipment with 

a 20-year delay. By this rule, the falling rate 

of fuel burn improvement identified in this 

report means that new equipment delivered 

in 2008 will burn 9% less fuel on average 

than the in-service fleet per seat-km of 

activity, compared to a 33% reduction from 

new aircraft delivered ten years ago relative 

to the 1998 in-service fleet. Absent 

dramatic, unforeseen improvements in the 

efficiency of new delivered aircraft over the 

next decade, the benefits of introducing new 

equipment will fall even further.11

A well-designed CO2 standard for new 

aircraft, adopted either through ICAO or by 

member countries, may help alleviate this 

trend provided that it sufficiently incentivizes 

the deployment of efficient technologies and 

designs. A CO2 standard that promotes both 

new aircraft and engine offerings and 

incremental improvements from inproduction designs would have the greatest 

impact on emissions. In particular, ICAO’s 

stated high-level preference for a CO2

standard for “new aircraft types” (ICAO 

2009b), which in essence would grandfather 

in existing production lines and possibly 

derivative products as well, could prolong 

the current period of limited efficiency 

improvements by delaying the introduction 

 7 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008
of new aircraft designs by manufacturers 

wishing to avoid triggering the standard. A 

broader standard affecting all inproduction designs would 

promote the timely 

deployment of efficiency 

innovations and would likely 

be more effective as a result. 

Given the outlook for 

continued growth, marketbased measures to constrain 

demand growth and accelerated 

improvements in operational efficiency will 

also be needed to meet the climate protection 

goals being discussed today (Lee et al. 2009). 

 8 Policy Implications
9 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008 

APPENDIX B: SENSITIVITY 

ANALYSIS

Two simple sensitivity analyses – one on 

mission length, and the other on the potential 

for year on year improvements within an 

aircraft-engine combination – were 

conducted on the results summarized in 

Section 3. 

DESIGN RANGE VERSUS 

OPERATIONAL RANGE

This report aims to estimate the efficiency of 

new aircraft as designed. Consistent with 

that aim, the seat-km and ton-km fuel burn of 

representative aircraft models were estimated 

at design ranges, either maximum range with 

a design payload (seat-km), or maximum 

range at maximum payload (ton-km). 

Term Explanation

Aircraft model An aircraft production family, e.g. B757, B767 etc.

Aircraft series A variant within an aircraft model, e.g. 767-200, 767-300, etc.

Activity A measure of use. Here, block hrs per year.

Available flight level The flight altitudes allowed to an aircraft. Multiplying flight level by 100 feet 

gives nominal (“pressure”) altitude.

Available seat-km (ASK) A measure of capacity (passengers only) on commercial aircraft.

Available tonkm (ATK)An aggregate measure of aircraft capacity for passengers plus cargo on 

commercial aircraft.

Aviation-induced cloudiness Impact of aviation emissions on cloud formation, including contrails and 

secondary cirrus formation.

Belly freight Non-luggage cargo carried on passenger aircraft.

Block hours Gate to gate hours in operation, including taxi, takeoff, and landing. 

Block fuel burn Gate to gate fuel burn

Delivery

When a new aircraft is provided to an airline. Used for weighting instead of 

sales due to large time lag between signing a purchasing contract and actual 

delivery. 

Design range 

A design parameter denoting the maximum range an aircraft can fly at full 

load, either all seats filled (passengers only) or at maximum payload 

(passengers plus cargo). 

Engine model An engine production family, e.g. TRENT, JT9D, etc.

Engine series A variant within an engine model, e.g. TRENT 772, 900, etc.

Fuel burn A fuel consumption term for an entire aircraft. Typical units are grams of fuel/

ASK or fuel/ATK.

High bypass ratio turbofans Large, efficient modern jet engines with low fuel consumption and relatively 

high NOx emissions. 

Maximum takeoff weight 

(MTOW) A regulatory maximum weight of a loaded aircraft at takeoff.

Maximum zero fuel weight 

(MZFW) The maximum weight of an aircraft minus fuel.

Narrowbody aircraft Single isle aircraft used to serve short-haul and regional routes. 

New aircraft types A regulatory term denoting new aircraft designs.

Operating empty weight (OEW) The weight of an aircraft without payload or fuel.

Specific air range Air distance traveled per unit of fuel burn (km/kg).

Radiative forcing (RF)

A measure of a change in the balance of energy entering and exiting the 

Earth’s atmosphere. Used to predict climate impacts such as temperature, 

drought and precipitation changes.

Regional jets Small, single-aisle jet aircraft used on regional routes.

Revenue seat kilometers (RSK) A measure of passengers moved, calculated as ASK times a load factor.

Widebody aircraft Dual aisle aircraft typically used to serve high-capacity medium and long-haul 

routes. 

APPENDIX A: GLOSSARY 
10 Appendix B 

Modern commercial aircraft are typically 

designed for extreme rather than 

representative missions, allowing airlines to 

reduce capital and some operational costs by 

flying a single aircraft model on a large 

variety of missions. Aircraft are most often 

operated on flight lengths considerably 

shorter than their designed range. 

While the practice of flying aircraft on 

missions well below their design range 

reduces system wide efficiency12, aircraft do 

burn more fuel at design lengths than shorter 

ranges due to the need to “burn fuel to carry 

fuel.” It is therefore useful to consider 

whether this paper’s primary findings are 

sensitive to assumption of stage length. 

Table B-1 summarizes the results of a 

sensitivity test with respect to mission 

length, using flight lengths of 900 km for 

narrowbody aircraft and regional jets and 

5400 km for widebody aircraft in place of 

design ranges. Where either range exceeds 

maximum range at maximum payload for the 

ATK metrics, maximum range at maximum 

payload was used instead. 

As Table B-1 indicates, with the exception of 

seat-km improvements from 1990 to 2008, 

our results are broadly insensitive to 

assumptions about range. The flattening of 

improvement after 1990 is in fact more 

pronounced using simulated operational 

ranges in place of design ranges. 

The most significant difference, the annual 

rate of post-1990 improvement on a seat-km 

basis, appears to be attributable to a slower 

rate of improvement post-1990 for 

narrowbody aircraft and regional jets 

operating inefficiently at very short stage 

lengths. 

INCREMENTAL IMPROVEMENTS 

WITHIN AN AIRCRAFT TYPE

The second major way in which this study’s 

findings may be sensitive to assumptions 

relates to the potential for hypothetical yearon-year improvements within an aircraft 

type. Since this analysis uses static 

representative Piano models to estimate fuel 

burn, it is not clear how possible year-onyear improvements (e.g. engine 

modifications, minor aerodynamic 

improvements such as reshaping pylons, etc.) 

within a given aircraft and/or engine series 

are handled. Industry sources typically 

assume some level of improvement within an 

aircraft design through incremental 

improvements over its production life. 

Where improvements over time within an 

aircraft model are linked to a change in series 

(-100 to -200) or a new aircraft/engine 

combination within a given series, in many 

cases this leads to a change in representative 

Piano models and a subsequent change in 

estimated fuel burn. Relative reductions in 

fuel burn by delivery year are observed 

within most major in-production narrow and 

widebody aircraft families (Table B-2, 

negative values imply an increase in fuel 

burn). Incremental changes that do not 

translate to a new aircraft series name or 

aircraft/engine combination are a more 

TABLE B-1. SENSITIVITY ANALYSIS ON MISSION RANGE

Metric Case Annual improvement Cumulative 

Improvement Metric Case 1960-1990 1990-2008

Cumulative 

Improvement

Seat-km

Baseline 2.1% 0.40% 103%

Operational Range 2.1% 0.22% 92%

Variation -4% -44% -11%

Ton-km

Baseline 2.0% 0.62% 103%

Operational Range 2.0% 0.52% 98%

Variation -1% -16% -4%
11 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008

difficult issue, although we note that those 

reductions might also be expected to be 

smaller than the annual improvements values 

summarized in Table B-2.13 

To test the sensitivity of our results to yearon-year improvements within a given aircraft 

type, we here assume that a given aircraft 

engine combination continues to improve in 

efficiency by 0.25% annually after their 

introduction. For example, a 777-200 with a 

TRENT 892 engine delivered in 2007 is 

assumed to have only 97.5% (1/1.002510) the 

fuel burn of one delivered in 1997. This 

value is consistent with previous industry 

projections of future aircraft efficiency 

improvements, and due to the manner in 

which Piano models are calibrated is likely to 

overestimate the magnitude of year-on-year 

improvements within an aircraft design.14 

The results of this sensitivity analysis are 

shown in Table B-3.

As with mission range, our results are largely

insensitive to assumptions about year-onyear improvements within an aircraft series, 

with aggregate and annual fuel burn 

reductions assuming incremental 

improvements within a given aircraft design 

being about 1 to 3% larger over the long run 

and prior to 1990 than without. Consistent 

with the understanding that the average age 

of aircraft production lines has increased 

significantly after 1990, the assumption of 

incremental improvements increases the 

annual modelled fuel burn reduction by 14% 

and 9% for ASK and ATK, respectively, over 

baseline conditions. This does not change the 

primary findings regarding the falling pace 

of efficiency improvements since 1990. 

APPENDIX C: COMPARISON 

WITH PREVIOUS WORK

As noted in Section 1, industry, academic, and 

research organizations have in the past made 

efforts similar to that summarized in this 

paper to estimate long-term improvements in 

new aircraft fuel burn. While all of these 

studies save Thomas et al. (2008) have found 

TABLE B-3. SENSITIVITY ANALYSIS ON INCREMENTAL EFFICIENCY IMPROVEMENTS 

Metric Case Annual improvements Cumulative 

Improvement Metric Case 1960-1990 1990-2008

Cumulative 

Improvement

Seat-km

Baseline 2.1% 0.40% 103%

YoY improvement 2.2% 0.46% 106%

Variation 1% 14% 3%

Ton-km

Baseline 2.0% 0.62% 103%

YoY improvement 2.0% 0.67% 106%

Variation 1% 9% 3%

TABLE B-2. ESTIMATED ANNUAL EFFICIENCY IMPROVEMENTS BY AIRCRAFT FAMILY 

Family Year of Delivery # of Piano-X 

models

Implied annual eff. change Family First Last1# of Piano-X 

models ASK ATK

B737 1967 2008 17 1.0% 0.8%

B747 1969 2005 7 1.0% 0.8%

B757 1982 2005 6 0.2% 0.3%

B767 1982 2008 5 0.2% 0%

B777 1995 2008 6 0.3% 0.2%

A320 1988 2008 10 0% 0%

DC-8 1959 1972 2 0.1% 0.9%

DC-9 1965 1982 2 0.3% 0.4%

DC-10 1971 1989 2 -1.4% 0.2%

MD-80 1980 2000 5 -0.2% 0.2%

[1] Passenger aircraft only. Dedicated freighter deliveries may be continuing.
12 Appendix C 

a falling rate of new aircraft fuel efficiency 

improvement over time, the relative 

magnitude of total fuel burn reductions varies. 

This appendix compares study results and, 

where possible, offers tentative suggestions 

for the differences in results. 

Table C-1 summarizes the previous studies

considered in this paper. 

As shown in Table C-1, this analysis has 

generated the smallest estimated fuel burn 

reduction of the studies to date. While a lack 

of transparency in methodology and 

assumptions for many of these analysis, 

particularly Thomas et al. (2008) make 

comparison difficult, these differences are 

likely attributable primarily to the following:

1. This report’s use of sales-weighting, 

which minimizes the influence of 

commercially unimportant models 

and reflects the fact that older, lessefficient aircraft models often 

continue to be produced for years 

after a more efficient model or 

configuration has been introduced.

2. The inclusion of short-haul aircraft 

(narrowbody and regional jets), 

which tend to be less efficient than 

widebodies on certain missions, 

particularly on a ton-km basis. 

A more detailed comparison with each of the 

studies summarized in Table C-1 is provided 

below. 

ROLLS-ROYCE, CITED IN ALBRITTEN 

ET AL. "GLOBAL ATMOSPHERIC 

EFFECTS OF AVIATION.” (1997)

While not discussed in the original Albritten 

report, upon request Rolls-Royce provided 

general information about methods and 

assumptions underlying its analysis, including 

seat counts (three class seating for all aircraft), 

load factor (70%), range (1850 km), and 

payload (passenger to mass conversion factor 

of 100 kg used). While a detailed sensitivity 

analysis could not be conducted due to time 

constraints, we offer the following possible 

reasons for the higher fuel burn reduction 

estimated in that graph:

• The analysis is not sales-weighted. 

As a result, the Rolls-Royce trend 

line should act as a leading indicator 

for efficiency in that it overweights 

new designs relative to their 

prevalence in a given year’s delivery 

mix. 

• The report started its trend line with 

the unusually inefficient Hawker 

Siddeley Comet-4 (76 deliveries 

between 1958 and 1967 in all 

configurations), rather than the more 

efficient and more commercially 

successful Douglas DC-8 family 

(319 deliveries over the same period) 

or the Boeing 707 family (504 

deliveries). This generated a high 

baseline and therefore a larger 

reduction.

TABLE C-1. COMPARISON OF RESULTS TO NOTABLE PREVIOUS WORK 

Source Metric Period Reduction (%)

Rolls-Royce, cited in Albritten et al. (1997) fuel/ASK 1960-1997 70%

Lee et al. (2001) fuel/ASK 1960-1995 64%1

Peeters et al. (2005) fuel/ASK 1960-2000 55%

Thomas et al. (2008) fuel/RSK2 1960-2010 82%

This study fuel/ASK 1960-2008 51%

fuel/ATK 51%

[1] 1960-2000, as estimated from power curve relationship by Peeters et al. (2005).

[2] Implied – see discussion below.
13 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008 

• As noted above, the analysis 

excludes short-haul narrowbodies 

and regional jets, which might be 

assumed to adopt fuel efficiency 

technologies more slowly than longhaul aircraft. 

• Assumption of three class seating 

(first, business, and economy class) 

for early long-haul jets likely leads to 

lower seat counts and therefore 

higher fuel burn on a seat-km basis 

relative to Piano for 1960’s and 70’s 

era aircraft. Since airlines began 

using business class around 1980, 

those seat counts may be 

representative of older aircraft inservice since that time rather than as 

delivered in the 1960’s and 70’s, the 

focus of this report.

LEE ET AL. “HISTORICAL AND FUTURE 

TRENDS IN AIRCRAFT PERFORMANCE, 

COST, AND EMISSIONS.” (2001)

While this study aimed to cover in-fleet 

efficiency improvements broadly, including 

operational improvements and technology 

introduction into the in-service fleet, an 

estimate of new aircraft efficiency 

improvement (Eu, or aircraft energy usage) 

was provided. The following general 

observations may be made:

• 31 representative aircraft were 

chosen representing prominent 

widebody and narrowbody designs. 

Consistent with the focus on the 

period to 1995, relatively inefficient 

yet commercially important regional 

jets do not appear to have been 

included. 

• The contribution of new equipment 

to in-service fleet efficiency 

improvements was estimated from 

the Breguet range equation using 

aggregate, publicly sourced 

variables, supplemented and verified 

by industry sources. Some input 

variables to the Breguet equation 

(e.g. SFC, L/D) deviate from their 

cruise values at takeoff which may 

influence the estimated share of 

efficiency improvements contributed 

by new equipment to block fuel use, 

the focus of this study. 

• Given the reliance upon actual inservice data, it is unclear how the 

inclusion of belly freight in the 

analysis impacts the estimated seatkm fuel burn of passenger aircraft 

(recall that our study intentionally 

excludes belly freight from its 

estimation of fuel burn/ASK). 

PEETERS ET AL. “FUEL EFFICIENCY OF 

COMMERCIAL AIRCRAFT: AN 

OVERVIEW OF HISTORICAL AND 

FUTURE TRENDS.” (2005)

As shown in Table C-1, owing to similarities 

in methodology the estimate of 55% reduction 

in fuel burn from 1960 to 2000 on an ASK 

basis most closely matches this study’s 

estimate. Key reasons for the smaller 

discrepancy may include:

• The use of the Boeing 707-320, 

rather than the Comet-4, as the start 

point for the analysis. Use of the 

737-200, an efficient and 

commercially successful model, 

should provide results closest to that 

obtained by sales-weighting.

• The inclusion of one modern 

narrowbody aircraft, the Boeing 

B737-800 with winglets. Note that 

regional jets were not included. 
14 References 

THOMAS ET AL. PLANE SIMPLE TRUTH: 

CLEARING THE AIR ON AVIATION’S 

ENVIRONMENTAL IMPACT. 2008.

This analysis, which has been cited 

prominently by the International Air Transport 

Association (IATA 2009), estimated unusually 

large fuel efficiency improvements that 

crucially do not tail off over time per every 

other analysis. Since no detail was provided 

on methods by the authors in their book, nor 

made available upon request, it is impossible 

to adequately compare results beyond the 

following general observations:

• The analysis appears to be an 

extrapolation of the Rolls-Royce 

figure (Albritten 1997), with the 

same methodological differences 

discussed above holding true here. 

• The post-1997 fuel burn reductions 

for new aircraft do not appear 

supportable in light of manufacturer 

claims and independent modeling 

results. For example, fuel burn 

reductions attributed to the A380 and 

B787 (estimated from the figure as 

approximately 40% and 45% 

reductions from the aircraft they are 

meant to replace, respectively), are 

more than double that advertised by 

their manufacturers. One possible 

explanation is that operational 

improvements, particularly increasing 

load factor, have been mixed with 

pure technology improvements, 

making the applicable metric fuel 

burn per revenue seat kilometer 

(RSK).

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Air Transit Association (ATA). 2009. “Quarterly

Cost Index: U.S. Passenger Airlines.” Electronic 

resource, accessed at http://www.airlines.org/

economics/finance/Cost+Index.htm. 20 October.

Albritton, D.; Amanatidis, G.; Angeletti, G.; 

Crayston, J.; Lister, D.; McFarland, M.; Miller, J.; 

Ravishankara, A.; Sabogal, N.; Sundararaman, N.; 

and Wesoky, H. 1997. "Global atmospheric effects 

of aviation. Report of the Proceedings of the 

symposium held on 15-19 April 1996 in Virginia 

Beach Virginia, USA." NASA CP-3351, NASA, 

Washington. 

Bows, A.; Upham, P.; Anderson, K. 2005. 

“Growth Scenarios for EU & UK Aviation: 

Contradictions with climate policy.” Tyndall Centre 

for Climate Change (North), The University of 

Manchester. 16 April.

Carson, S. 2009. “How Boeing Fights Climate 

Change.” Wall Street Journal. 23 May.

Eyers, C.J. 2004. “AERO2k Global Aviation 

Emissions Inventories for 2002 and 2025.” QinetiQ 

Ltd. pp. 59 to 76. December. Available at http://

www.aeronet.info/fileadmin/aeronet_files/links/

documents/AERO2K_Global_Aviation

_Emissions_Inventories_for_2002_and_2025.pdf.

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International Air Transport Association (IATA). 

2009. IATA Technology Roadmap. Third Edition.

International Civil Aviation Organization (ICAO). 

2009a. “Aviation’s Contribution to Climate 

Change.” HLM-ENV/09-IP/04. 2 October.

ICAO. 2009b. “Elements of an ICAO Position for 

COP15.” HLM-ENV/09-WP/12. 2 October.

ICAO. 2001. Committee on Aviation 

Environmental Protection (CAEP): Report of the 

Fifth Meeting. Montreal, 8–17 January 2001.

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(ICSA). 2009. “ICAO Scoping Analysis on a 

Potential CO2 Standard for New Aircraft.” 

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documents/CO2scopinganalysis.pdf.

Lee, D; Fahey, D., Forster, P.; Newton, P; Wit, R.; 

Lim, L; Owen, B; Sausen, R. et.al. 2009. “Aviation 

and global climate change in the 21st century.” 

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22-23, Pages 3520-3537. July. 

Lee, J.; Lukachko, S.; Waitz, I.; Schafer, A. 2001. 

“Historical and Future Trends in Aircraft 

Performance, Cost, and Emissions.” Annual. Rev. 

Energy Environ. 26:167–200.
15 Efficiency Trends for New Commercial Jet Aircraft, 1960 to 2008 

Peeters, P.M.; Middel, J.; Hoolhorst, A. 2005. Fuel 

efficiency of commercial aircraft: an overview of 

historical and future trends. NLR-CR-2005-669. 

National Aerospace Laboratory. November. 

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McFarland, M. 1999. Aviation and the Global 

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Airframe Standard.” International Council on Clean 

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C.; Pepper, R. 2008. Plane Simple Truth: Clearing 

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ENDNOTES 

1 Since the CO2 emitted from an aircraft in flight is 

inversely related to its efficiency, these terms are 

synonymous. 

2 See ICSA (2009) and Rutherford (2009) for 

further details regarding critical issues for standard 

design. 

3 Fuel burn is a common industry measure of the 

efficiency of an entire aircraft (airframe plus engine 

combination). These and other terms are defined in 

the Glossary in Appendix A.

4 Information available at www.lissys.demon.co.uk/

PianoX.html. 

5 Previous versions of Piano have been used in 

ICAO work on aircraft efficiency, and the model 

itself was extensively validated during the 

development of the European Community’s 

AERO2k emissions inventory (Eyers 2004). Piano 

fuel burn and emissions estimates have also been 

used as the basis for ICAO’s carbon calculator and 

Manchester Metropolitan University’s FAST 

model.

6 For most transport modes, fuel efficiency is 

calculated as a sales-weighted average to ensure 

that the prevalence of popular models is adequately 

reflected in industry or corporate averages. For 

aircraft, the long delay between an order and that 

aircraft entering into service makes aircraft 

deliveries the proper basis for calculating a 

weighted average. For simplicity’s sake we refer to 

this as “sales weighting” throughout this paper.

7 During external review of this draft analysis, the 

original 737-200 in Piano-X was found to be 

representative of significant post entry-into-service 

improvements, necessitating this change. The 

updated versions of all representative aircraft are 

included in the most recent Piano-X database.

8 Fuel burn is inversely related to fuel efficiency, so 

a 50% reduction in fuel burn corresponds to a 

doubling of fuel efficiency. By convention in this 

paper we refer to a reduction in fuel burn in figures 

as an increase in aircraft efficiency.

9 The replacement of efficient turboprop aircraft 

with less efficient regional jets, which offer speed, 

noise, and perceived safety advantages to 

consumers but can consume 20% more fuel than 

the turboprops they replace, is another recent 

example of prioritizing performance over fuel burn. 

10 Increased performance may be also linked to a 

strategy of reducing the optimization of new 

aircraft designs around specific missions, which 

reduces costs for manufacturers by allowing them 

to market fewer aircraft designs. Note, for 

example, Boeing’s decision to discontinue 

production of mid-range aircraft (the 757 and 767 

families) and to replace the 767 family with 787 

Dreamliner. The 787-8 is more similar to a longhaul 777 than a 767 model in terms of speed, range, 

and cargo capacity: as a result, the 787 is expected 

to offer little if any reduction in seat-km fuel burn 

when flown on missions previously served by the 

767-300 ER. See Figure 7, in Rutherford (2009). 

11 Recent industry presentations to ICAO (ATAG 

2009) estimate a maximum efficiency improvement 

for new aircraft of 1.16% per annum through 2050. 

Improvements of this magnitude would require a 

much faster pace of new aircraft and engine 

introduction than has occurred over the past two 

decades. 

12 For example, aircraft designed for 4000 km 

missions are less efficient when flown on 1000 km 

routes than an equivalent aircraft optimized around 

that flight length due to excess wing, engine, and 

fuel tank weight. Operational efficiencies could 

therefore be improved significantly through greater 

optimization of aircraft to individual missions, 

albeit at a cost to airlines.

13 If not, the introduction of a new aircraft series 

within a given family would be associated with an 

increase in fuel burn.

14 Piano’s representative models are calibrated via 

comparison to available data from actual aircraft at 

a variety of stages during their production, with 

some near the start and others near the end of 

production cycles. As a result, some of the 

incremental year-to-year improvements may 

already be captured.

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