Direct and indirect energy use for commercial aviation

DIRECT

AND INDIRECT COMMERCIAL

ENERGY USE FOR AVIATION

ERIC.HIRST* Office of Fncrgy

(‘onstxvation.

Federal

Energy Oftice. Washington

D.C. 20461. U.S.A

Abstract Commercial aviation is important from an cncrgq standpoint for two reasons. First. airplanes arc the most energy-intensive mode for either freight or passengers. Second, airline traffic is growing much more rapidly than is overall intercity trat?ic. Thus airplanes are likely to consume a larger fraction of the

transporlation energy budget in the future than they do now. In IY71. fuel use for commcrc~al alrplane propulsion amounted to IOXO trillion B.t.u.. O-3 per cent ol the transportation direct fuel use budget. This includes fuel used by both certificated and supplemental carriers. General aviation consumed an additional 100 trillion B.t.u. in 1971. Indirect energy uses for commercial air service -which includes energy used for petroleum refining. airplane manu!&turing. repairs. maintenance, other fuels and electricity, food for passengers. etc. totaled 370 trillion B.t.u. in 1971. Thus total energy demand for commercial air service in 1971 was 1450 trIllion B.t.u. 1 per cent of the national energy budget. Atrcraft fuel use accounts for three-fourths of total airline energy use. The energy associated with crude oil extractlon. transportation. and refining adds another I5 per cent. Airplanes, engines. and parts: other fuels and clectricit) : food for passengers: and airport construction and maintenance each contribute onI4 I 3per cent oftotal cncrgy use.

INTRODUCTION

This paper examines total (direct plus indirect) energy use for domestic commercial airline travel. Direct fuel use for commercial airplane propulsion amounted to 1080 trillion B.t.u. in 1971, 6.3 per cent of the transportation direct fuel use budget. (In 1971 transportation fuel use totaled 17.100 trillion B.t.u.; national energy use totaled 68.700 trillion B.t.u.) This fuel includes that used for both the certificated carriers (usually called the scheduled airlines) and the supplemental (nonscheduled) carriers. Indirect energy consumption for commercial air service-which includes energy used for petroleum refining, airplane manufacturing, repairs, maintenance, other fuels and electricity, food for passengers. etc.----totaled 370 trillion B.t.u. in 1971. Thus. total energy demand for commercial airline service in 1971 was 1450 trillion B.t.u., 2 per cent of the national energy budget. Airplanes are important from an energy standpoint for two reasons. First, airplanes are the most energyintensive transport mode for both passengers and * Research Engineer. ORNL-NSF Environmental Program. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830. Work described here was sponsored by the National Science Foundation RANN Program under Union Carbide Corp. contract with the U.S. Atomic Energy Commission. Prcscnt address: OlIice of Energy Conscrvatlon and Fn\ironment. Federal Energy Administration. Washington. D.C. 70461 U.S.A. 421

freight (Table 1). For freight, airplanes require I5 times as much fuel per ton-mile as do trucks and 60 times as much fuel per ton-mile as do trains. Of course. airplanes are also ten times as fast as other modes. For passenger travel, commercial airplanes are 2.5 times as energy intensive as cars and almost six times as energy intensive as’buses. Second, airline passenger and freight traffic is growing rapidly. Between 1950 and 1971. total intercity passenger travel increased at an annual average rate of 4.3 per cent, and total intercity freight traffic grew by 2.4 per cent per year. During this period, Ltirlinr passenger and freight traffic increased by more than 12 per cent annually.

DIRECT

ENERGY

USE

Table 2 summarizes traffic and fuel use statistics for civil aviation in the United States from 1950 to 1971. Civil aviation includes commercial aviation (both scheduled and nonscheduled carriers) and general aviation (private aircraft). While commercial air traffic grew 12.5 per cent annually. fuel use increased even more rapidlyI5 per cent per year. Figure I shows direct energy intensiveness (EI) for commercial and general aviation during this 2l-yr period. The method used to distribute fuel between passenger and freight traffic is described by Hirst

E. HIKSI

Mode AirpIano Truck Railroad Watcrwal I’ipclinc

Freight B.t.u.,‘ton-rmlc 11.000 2.700 700 570 450

Passcngcrs Mode

B.CU.. passenger-mile

Airplane commercial gt2ncral aviation Automobile Railroad Bus

x300

IO.300 izoo 7700 I500 _

* Thcx energy intensiwness values arc national averages -~ratios of total fl~cl used LO total carried by each mode. These values dcpcnd strongly on each mode‘s operating charactcrlstics factor. trip length. speed. equipment type. etc. Sources: Hurst (1973). Mutch (19731). Trans. Assoc. Amwicn I 1972). (1973): the calculation yields an energy equivalence 01 400 pounds of freight = one passenger. Between I950 and the early 1960’s. EI for commercial aviation incl-cased by 75 per cent. This sharp increase W;IS due to declining load factors (load factor is the fraction of capacity actually used) and the introduction of turbojets in the late 1950’s (Mutch. 1973b). Turbojets are considerably lister than piston-engine planes but consume more fuel per seat-mile. While load factors continued to generally decline during the 1960’s. El improved slightly as the more clliclcnt turbol’an engines replaced the turbojets. The

trallic IOXd

net result was a 197 I EI almost 60 per cent higher than the 1950 El. However. if the 1971 load factor had equalled the 1950 load factor. El in 1971 would ha\c been only 20 per cent higher than in 1950. Considering that the average speed of commercial air travel increased from less than 200 m.p.h. in 1950 to more than 400 m.p.h. in 1971. the increase in El stems small. Apparently, the combination of larger airplanes, higher cruise altitudes. longer stage lengths. and more eflicient engines partialI! olkct the fticl pcnalt! of higher speeds. General aviation pxscngcr trallic 21-c\\ ;I( the \;IIIIC‘ rate as cominct-cial aviation traltic (Table 2); hmc\ct-. lid use grew more slowly. Figure I she\\ s hoL+ general aviation El declined. due primarily to increased occtlpanty. which doubled during this time. Ncvcrtheless. El for general aviation is still higher than El for commercial aviation. ORNL-DWG

r

k

50

i > ?J

20

I

I

; GENERAL

10 1950

I

2.

Fuel ue

lor cllil

I

AVIATION

1960 FIs.

74-1478

1970

abiatlon

Direct

and indirect

energy use for commercial

429

aviation

Table 2. Air traffic and fuel use Commercial Traffic (IO” PM)*

1950 1955 I960 I965 I970 1971

9.3 21 32 54

I IO III I ‘.5”,,

* PM = passenger t TM = ton-mile. $ Estimate. Sources:

aviation

(IO’ TM)t

General

aviation

Fuel

Traffic

Fuel

(10” B.t.u.)

(10’ PM)*

(10” B.t.u.)

0.8 1.5 2.3 4.4 9. I 9.3

133 23 29 43 94 96

124”b

I O.O?<,

0.30 55: 0.49 120 0.89 260 I.9 530 3.4 1080 3.5 1080 Avjerage annual growth rate I ?I”,, I5,3”,,

milt.

Civil Aero. Bd. (1972a). Mutch (1973a). Trans. Assoc. America

During this 21-yr period. general aviation typically accounted for 8 per cent of total air passenger traffic and IO per cent of civil aviation fuel use. Overall. civil aviation fuel use grew by 14.5 per cent per year between 1950 and 1971 (Fig. 2). Rising traffic accounted for about X5 per cent of this fuel use growth, while increases in EI accounted for the remainder.

In addition to the fuels used for motive power, energy is needed to extract, transport. and refine oil; to manufacture. maintain and repair airplanes; to construct and maintain airports; and to carry out other air-travel-related activities. Energy Input!‘Output (I/O) coefficients for 1963 developed by Herendeen (1973) are used to derive estimates of these indirect energy uses. (1963 is the latest year for which I;0 data are currently available.) These coefficients. expressed in terms of B.t.u. per dollar, are multiplied by the dollar costs of various air-travelrelated activities. Financial data reported quarterly by individual air carriers to the Civil Aeronautics Board (CAB) form the basis for the dollar figures used here. The Air Transport Association of America. ATA. (1971) aggregates these data for the domestic trunk airlines. The domestic trunks account for almost 90 per cent of total domestic air carrier traffic. The CAB (1972b) (and ATA) forms give operating expenses divided into 11 “functional” categories such as flying operations, direct maintenance, passenger service. and depreciation and amortization. Expenses are also classified in terms of about 80 “objective” categories such as pilots and copilots. communications. aircraft fuels and oil, food expenses, insurance, and taxes. The result is a matrix that defines each airline

(1972).

expenses in terms of both functional and objective categories. Starting with the 1970 ATA data, the objective classifications were aggregated to 27 categories but the 11 original functional categories were retained. Each element of the resulting 27 x 11 element matrix was increased by the ratio of total domestic airline expenses (CAB, 1972a) to domestic trunk expenses (ATA, 197 I). This matrix provided a detailed estimate of operating expenses during 1970 for all domestic commercial airline service. One (or more) I/O sector was then assigned to each element of the airline-operating-expense matrix. Energy coefficients for “aircraft fuels and oil” and for “light, heat, power, and water” were estimated directly (CAB, 1972a). All other coefficients were obtained from Herendeen (1973). The energy coefficients were scaled from 1963 to 1970 by use of the ratio-total national energy use/GNP-for the two years. The resulting energy coefficients were then multiplied by the dollar figures in each element to yield energy costs associated with each element. The sum of all these energy figures is the estimated total energy use for commercial airline service. Energy uses for 1963 were estimated by multiplying the original energy coefficients by adjusted dollar figures. The dollar values were obtained by multiplying the total 1963 operating expense for each of the II functions (CAB, 1972a) by the fraction of the functional expense allocated to that objective category for 1970 (ATA, 197 1). These results are summarized in Table 3 for 1963 and 1970 with the I I functional categories aggregated to seven. Flying operations account for about 90 per cent of total energy use; this is almost entirely due to aircraft fuel use and the refining thereof (see Table 4, discussed below). Maintenance, aircraft and traffic ser-

430

I;lying operations

494 IS 7

Maintenance Passenger service Aircraft and trallic

servicmg Promotion and sales C;rnel-al and ndminlstration IXpreclatloll and

12 x 5 I-4

;illlortl/;itlon

Total

554

vicing, and depreciation and amortization each account for at least 2 per cent of total energy use. Table 4 summarizes total energy use in terms of objective categories. Aircraft fuel use accounts for three-fourths of total airline energy use. The energy associated with crude oil extraction. transportation. and refining adds another 15 per cent. Airplanes, engines, and parts; other fuels and electricity; food for passengers; and airport construction and maintenance each contribute only l-3 per cent of total energy use. The total energy use figures given in Tables 3 and 4 agree remarkably well with those obtained by Sebald and Herendecn ( 1973). who used a somewhat different method to derive these figures. (Their method. however, is also based on I!0 analysis.) Direct fuel use for airplanes is a larger fraction of total energy use than is the case for cars (75”0 vs 6O”J. This is, in part. because airplanes arc used more efficiently than cars: the typical airplane seat carries more than 100 times as many passenger miles annually as the average car seat does. Also. air traffic does not require highway construction. Finally, government Table 4. Total energy

subsidies to airlines (c.g. airport construction and maintenance. navigational aids. and direct payments to local-service airlines) are reflected in these calculutions only to the extent that they are covered by airport landing fees and airline taxes. Table 5 shows EI in terms of both direct and total energy uses for commercial air travel and for intercity auto travel. Although the ratio of total to direct energ) use is smaller for airplanes than for cars. airplanes are still twice as costly in terms of total energy impacts.

This analysis shows the total energy impacts of commercial aviation in the United States. Direct fuel use by commercial airplanes (1080 trillion B.t.u. in 1971) amounts to 6 per cent of direct fuel use for all domestic transportation. I.6 per cent of the total national energy budget. Indirect energy requirements are one-third as great as the direct fuel use. Thus. total energy demand for domestic commercial aviation in 1971 wab 1450 trillion B.t.u.. 2 per cent of national cnergq use.

use for commcrclal

aviation:

objccti\c

categories

I Y63

IO” B.t.u. Aircraft fuel use consumption refining Other fuels, electricity Airplanes, engines. parts Food for passengers Airport construction and maintenance* Other Total * Based on landmg

fees and taxes.

“,, of total cnergj

IO” B.t.u

404 x5 s

73 15

17 5

3

I

;

9 36 554

7 5 IO0

4 100

I

Direct and indirect

energy use for commercial

Table 5. Energy intensiveness of airlines and autos, 1971*

Commercial airlines freight (B.t.u./TM) passengers (B.t.u.iPM) Autos, intercity (B.t.u./PM)t

Direct

Total

42,000 8400 3300

56,200 11,200 5700

* TM = ton-mile; PM = passenger-mile. t Source: Hirst (1974). A number of assumptions and approximations were needed to perform this analysis. Direct fuel use data are probably reasonably accurate, although the EI values of Fig. I show year-to-year variations due to changes in load factor, stage length, cruise speed, altitude, etc. Unfortunately, things are more complicated with regard to indirect energy uses. Accuracy of the energy coefficients is limited by details of data collection and manipulation (Herendeen, 1973). Perhaps more important. the coefficients are based on 1963 data; the method used to scale them to 1970 ignores the possibility that these coefficients changed differently with time. The I/O sectors from Herendeen (1973) do not coincide exactly with the CAB (1972b) categories; personal judgment was required to align the two systems. Indirect energy uses were calculated for the domestic trunks. and then scaled up to account for all domestic commercial aviation; however. this scaling-up is unlikely to introduce significant errors because the domestic trunks account for almost 90 per cent of total domestic air carrier traffic. The method used to distribute direct and indirect fuel uses between freight and passenger service described by Hirst (1973) is approximate. The method yields an energy equivalence of 400 pounds of freight = one passenger. Mutch (1973b). on the other hand, used an equivalence of 200 pounds = one passenger ; Sebald and Herendeen (1973) used 250 pounds. In spite of these potential sources of error, these results should be useful in understanding the total energy impact of air travel and in evaluating airline energy conservation measures. Recently. a number of such measures have been suggested, including improved load factors, reduced cruise speeds, higher cruise elevations, shifts of short-haul traffic to other

aviation

431

modes, shifts to aircraft better suited to traffic on individual routes, and reduced delays. Mutch (1973b) and Pilati (1974) analyzed direct fuel savings due to adoption of airline conservation measures. The present analysis suggests that, on the auerage, in the long-run, these savings can be increased by one-third to account for the indirect energy savings. Some conservation measures, such as a reduction in short-haul flights, are likely to have larger energy savings, because short-haul flights involve higher maintenance costs, greater airport use, and higher passenger service costs on a passenger-mile basis than do longer flights. Other measures, such as reducing cruise speeds, are likely to have relatively small indirect energy savings. In all cases, however, the direct fuel savings can be increased by 20 per cent to account for the energy costs associated with crude oil extraction, transportation, and refining. REFERENCES

Air Transport Association of America (1971) Comparative statement of air carriers’ income-domestic trunk airlines. four quarters in 1970. Washington, D.C. Civil Aeronautics Board (1972) Hwdhoo~ of Aidiw Sruristic\. 1971 edition. Washington. D.C. Civil Aeronautics Board (1972) Uniform system of accounts and reports for certificated air carriers. Frderul Registrt 37 (I 84). part II. Washington, D.C. Herendeen R. A. (1973) The energy cost of goods and services. Oak Ridge National Laboratory No. ORNL-NSFEP-58. Oak Ridge, TN. Hirst E. (1973) Energy intensiveness ofpassenger and freight transport modes: 19X--1970. Oak Ridge National Laboratory No. ORNL-NSF-EP-44. Oak Ridge, TN. Hirst E. (1974) Direct and indirect energy requirements for automobiles. Oak Ridge NationalLaboratory No. ORNL-NSF-EP-64. Oak Ridge, TN. Mutch J. J. (1973) Transportation energy use in the United States: a statistical history. 1955~1911. Rand Corp. No. R-1391.NSF. Santa Monica. CA. Mutch J. J. (1973) The potential for energy conservation in commercial air transport. Rand Corp. No. R-1360-NSF. Santa Monica. CA. Pilati D. A. (1974) Airplane energy use and conservation strategies. Oak Ridge National Laboratory No. ORNLNSF-EP-69. Oak Ridge. TN. Sebald A. and Herendeen R. A. (1973) The dollar, energy and employment impacts of air, rail and automobile passenger transportation. Center for Advanced Computation No. 96, draft report. Univ. of Illinois. Urbana, IL. Transportation Association of America (1972) Transportation Fctcts and Trends, 9th edition. Washington. D.C.

R&sum&-Du point de vue de I’utilisation de l’energie, I’aviation commerciale est importante pour deux raisons. PremiZrement. les avions sont le moyen de transport de marchandises ou de passagers qui consomme Ic plus d’Cnergie. Deuxit!mement, la circulation akrienne croit bien plus rapidement que le trafic entre les grandes villes en g&&al. On peut done prkvoir que les avions consommeront une plus grande fraction du budget de I’Cnergie de transportation dans I’avenir qu’ils ne le font i prCsent.

332

F. HIKS~ En 1971. la consommatlon de carburant dcs a\ ions utill& connmcrclalcIiIcIIt \‘cle\a 2 IOXO trIllion\ de BTU. soit 6.3 pour cent du budget d’utilisation dxcctc du p2t1-olc pour IUS transports. (‘ccl comprcnalt I’essence utilist-e par les transporteurs agrCt_s et lcs autrcs. L’a~iation gi;nL:ralc con\omma 100 trIllion\ dc BTU de plus en 1971. L’utilisation indirccte d’Cnergle dnns l‘avlation commcrc~alc comprcn;~nt I’cncrg~c nt~l~\cc pour Ic raffinage du pktrolc. la construction des anions. lcs rt;p:uatlons. I’cntrctien. tl‘autrc\ fuel\ ct I’hlcctricitti. la nourriture des passagers. etc. SCmanta i 370 trillions dc BTL cn lY71, Ainsl. la clcmandc totalc d’i:ner.gic cn 1971 de I’aviation tiommcrcialc fut dc 1150 trillion\ dc BTC’. \olt 2 pour cent du hudgct national poutI’energic. L’essence pour anions represente Its trois quarts dc I’L;ncrglc toti~lc utillbcc par Ic\ il\1on5. L’Cncrglc iissocit?e 2 I’cxtraction du pCtrole brut. 5 son transport ct au rallinagc ;tloutcnt cncorc I5 pout cent.LCI a\ ions. les moteurs et les pi&es. les autrcs fuels ct I‘Clcctricitc. la nout-liturc dc\ pa\5;tfcr\. la con\trllction cl la maintenance dcs Groports contribuent mdl\lducllcmcnt sculcmcnt I pout-CC’II~ dc I’cnut-gee to!alc utillsL;c.

Zusammenfassung

Hinsichtllch des fnerglcvcrbr~tLlclis,ist die Ll\illuftfahrt au5 /\+cI Grtindcn angc\prochen: Erstcns verbraucht das Flugzcug hei der Bcflirderung {on Pn\sngicrcn und Frucht bcrglcichsweise die grliBten TreihstolTmengen. und llvcltcns sind die ZuwachSratcn am L.uItvcrLchr tchr vicl griiljcr als bci anderen Fernvcrkehrsmitteln. Aus dicscn Griinden ist /II cr\+artcn. da15 dcr Luft\ct-hehr 111Zukunft cincn griineren Anteil des Encrgiebudgcts im Verkchrsscl\tor bcanq~rucht aI\ hcutc. I971 bctrup dcr primare Energlc\crbrauch dcr Zivilluftfahrt ION) Trlllloncn Btu (Britische \Viit-mcclnhcltc~~). cntsprcchcnd 6.3 Pro/cnt dcs TrcihstotT\crbr;ILlchs ;IIIct- I’crkchra~~ittcl. DIG \‘crht;ltlcll\\\crtc gcl~cn 1‘111die L~nlcnund die Chartcrfluggesellschaften; die nichtgcwerhlichc Luftl’aht-t \crbt-auchtc 1m Jahr lY7 I /usiit/lich 100 TI-IIliil lionen Btu. Der mittelbarc Energievcrhrauch fiir die Treibsto~gc\vi~In~~~~~~g und den Fluycugbau. Rcparaturen und Wartungsarbeiten. fiir die Herstellung andercr Brcnnstoll’c sonic fur dlc St!-om\crsorI~ncl-giekongung. die Bordkiichen usw. belief sich 1971 auf 370 TrIllionen Btu. Damit betru g dcr gc~mtc sum dcr gewerblichcn Zivilluftfahrt im Jnhre 1971 1150 TI-illioncn Btu odcl- 2 Proxnt d~r inl:indischcn Energieverhrauchs. Vom Gesamtkonsum cntficlcn dabei 75 Proxnt auf clcn Trcih\tot~\cht~,r. 7uGtrlichc 15Proxnt wcrden fiir die Rohdlgewmnung. den Rohiiltrans[lot-t und die Trclb\t~~lfhsr~tcll~~ng ;Iufgc\+cIIuncl I r\;lt/lcllpri~~i~lhtl~~ll. dlC c;c\\ 1n11ung dct. Dagegen waren Flugrcughau. Trichwcrkher~tclltlng andercr Brcnnstofe. die Stromversorgung. der Borddicnht sowic Flughafcnbsu und -untcrhnltung mlt nut I 3 Prozcnt am Gesamtvcrbrauch bctelligt.