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Pounds of CO2 per mile in a plane

A plane produces about 244 pounds of carbon dioxide each mile it flies. An average plane carries 218 passengers, so that's about 1 pound of carbon dioxide per passenger per mile in the air.

Case study: The Babcock School

Tons of variables affect the carbon footprint of a plane - elevation, load, wind speed, engine age, and much more. However, we wanted to boil it down to a simple metric - CO2 per mile per passenger in the air. We knew how many students went on each school trip, and we knew the arrival and departure cities as well as the layovers along the route. A little math, and suddenly we knew how much carbon dioxide our student trips produced.

- Jack Clayton

1. Popular US-based airlines

to top | next step: 2. Planes in use at these popular airlines

To figure out how much carbon dioxide is created by a plane flying one mile in the air, we're going to need to look at the technical details of a bunch of planes. However, how do we know what planes to look at, and how will we weight the different performance data?

To answer those questions, we decided to select a bucket of industry-leading airlines, see what planes they fly, and weight the technical details of each plane with that plane's popularity.

There are plenty of ways to measure industry leadership, but we used the number of international departures from US airports as our measure of popularity. Here are the most popular US-based airlines in 2002 as reported by the Department of Transportation. (We know it's old data, and the airline industry has definitely seen some ups and downs since 2002. If you have better data, let us know.)

Exhibit 2.1 Popular US-based airlines in 2002

No. international departures from US airports

US-based airline Number of departures
American 1,695
Continental 1,157
Delta 860
United Airlines 827
Northwest 721
USAirways 543
TOTAL 5,803
Source: Aviation Industry Data, Office of Aviation and International Affairs, Downloadable Data, Departures 2002, US Department of Transportation

2. Planes in use at popular airlines

to top | previous step: 1. Popular US-based airlines | next step: 3. Sanity check: do Boeing's popular planes fly both domestic and international flights?

Now that we have an idea who our industry leaders are (a rough idea because the data is 6 years old!), we can see what planes they use. Determining which planes are used by our industry leaders will tell us what technical data we need to gather later so we can calculate average fuel efficiency.

These figures correspond to planes registered by the airline with the FAA. They may not necessarily be in use because an airline flies different planes on different routes depending upon a number of factors. Some planes don't get used at all. However, we can't really adjust for that, and since it is in the company's best interest to operate close to capacity, we'll run with these numbers.

Exhibit 2.2A Planes in use at major US-based airlines in 2007

No. planes registered with the FAA as of December 2007

Plane model American Continental Delta United Northwest USAirways Total as a % of total
B-737
77
255
71
94
0
92
589
21.6%
B-747
0
0
0
30
35
0
65
2.4%
B-757
140
58
123
97
71
43
532
19.5%
B-767
74
26
104
35
0
10
249
9.1%
B-777
47
20
8
52
0
0
127
4.7%
MD-88
0
0
120
0
0
0
120
4.4%
MD-90
0
0
16
0
0
0
16
0.6%
DC-9
338
0
0
0
134
0
472
17.3%
F-28
4
0
0
0
0
0
4
0.1%
A-300
34
0
0
0
0
0
34
1.2%
A-319
0
0
0
55
59
93
207
7.6%
A-320
0
0
0
97
71
75
243
8.9%
A-321
0
0
0
0
0
28
28
1.0%
A-330
0
0
0
0
29
9
38
1.4%
TOTAL
714
359
442
460
399
350
2,724
100.0%
Source: Airline Certificate Information, US Federal Aviation Administration

Examining the data in Figure 2.2A, we can see that nearly 60% of the planes used by our industry leading US-based carriers are made by Boeing (versus 20% made by Airbus, Boeing's closest competitor). Let's examine the popularity of Boeing's models against one another.

Exhibit 2.2B Popularity of Boeing planes

No. planes in use

Plane model Total planes in service as a % of total
Boeing planes in service
B-737
589
37.7%
B-747
65
4.2%
B-757
532
34.1%
B-767
249
15.9%
B-777
127
8.1%
TOTAL 1,562 100%
Source: data from Exhibit 2.2A

Now that we know Boeing provides the majority of planes used by our industry leading airlines, we'll assume they provide the majority of planes to the whole US-based airline industry. With that assumption, we can study the technical details of Boeing's planes to estimate the carbon dioxide produced by flying one mile in the air.

3. Sanity check: do Boeing's popular planes fly both domestic and international flights?

to top | previous step: 2. Planes in use at popular airlines | next step: 4. Fuel efficiency of Boeing's popular 7-series planes

Wait a second. We selected our sample of carriers based on international departures, but we're looking for an industry-wide average for both domestic and international flights. What if the basket of planes we're about to use to represent to entire industry only flies internationally.

When we checked Expedia to see which types of planes were used on a hypothetical trip between New York and London versus a hypothetical trip between Greensboro, NC and Atlanta, GA, we found several Boeing models used on both trips. In addition, since all Boeing models are available in domestic versions, we figured we were safe assuming our basket of planes could represent both domestic and international flights.

4. Fuel efficiency of Boeing's popular 7-series planes

to top | previous step: 3. Do Boeing's popular planes fly both domestic and international flights? | next step: 5. Average fuel efficiency for one mile in flight

Now that we're assuming Boeing's planes are the majority of US-based aircraft, we can set about estimating the average fuel economy of each Boeing 7-series of aircraft. Within each 7-series, there are multiple models, and for one model there are multiple cabin configurations. A two class configuration was chosen where available because we believed this was probably their most popular configuration - first or business class and coach.

To compute the fuel economy of each plane as gallons per mile, we divided the stated maximum fuel capacity in gallons by the stated maximum range in statute miles (miles we drive in a car). Since Boeing's reported maximum range would have to include takeoff, flight, and landing we figured this was a simpler approach than using a more complex multivariate equation. In addition, in their technical details, Boeing wants to overstate both the range and the fuel capacity. Hopefully, any overstating will wash out in the division to create a close or conservative figure.

Exhibit 2.4 Fuel efficiency of Boeing's planes

units marked in columns

Model # Passengers
(2 class config)
Max Fuel Capacity
(gallons)
Max Range
(nautical miles)
Max Range
(statute miles)
Gallons per statute mile
(gal / mi)
737
         
737-600
110
6,875
3,050
3,510
1.96
737-700
126
6,875
3,365
3,872
1.78
737-700ER
76
6,875
5,510
6,341
1.08
737-700C
120
6,875
3,205
3,688
1.86
737-800
162
6,875
3,060
3,521
1.95
737-900ER
180
7,837
3,200
3,682
2.13
AVERAGE
129
7,035
3,565
4,103
1.79
 
 
 
 
 
 
747
 
 
 
 
 
747-8
467
64,225
8,000
9,206
6.98
747-400
524
57,285
7,260
8,355
6.86
747-400ER
524
63,705
7,670
8,826
7.22
747-100
452
48,445
6,100
7,020
6.90
747-200
452
52,410
7,900
9,091
5.76
747-300
496
52,410
7,700
8,861
5.91
AVERAGE
486
56,413
7,438
8,560
6.61
 
 
 
 
 
 
757
 
 
 
 
 
757-200
200
11,489
3,900
4,488
2.56
757-300
243
11,466
3,395
3,907
2.93
AVERAGE
222
11,478
3,648
4,197
2.75
 
 
 
 
 
 
767
 
 
 
 
 
767-200ER
224
23,980
6,590
7,584
3.16
767-300ER
269
23,980
5,975
6,876
3.49
767-400ER
304
23,980
5,625
6,473
3.70
AVERAGE
266
23,980
6,063
6,978
3.45
 
 
 
 
 
 
777
 
 
 
 
 
777-200
400
31,000
5,235
6,024
5.15
777-200ER
400
45,220
7,700
8,861
5.10
777-300
451
45,220
6,015
6,922
6.53
777-200LR
301
47,890
9,450
10,875
4.40
777-300ER
365
47,890
7,930
9,126
5.25
AVERAGE
383
43,444
7,266
8,362
5.29
Source: Boeing's Website, Aircraft Technical Details

5. Average fuel efficiency for one mile in flight

to top | previous step: 4. Fuel economy of Boeing's popular 7-series planes | next step: 6. Amount of CO2 produced by one mile in flight

Now we know the fuel efficiency of each Boeing model. We can combine that fuel efficiency data with popularity data to figure out how much carbon dioxide is produced on average when you fly one mile in any Boeing plane (in geek speak, we're going to create a weighted average). However, since Boeing provides the majority of planes to the US airline industry, we can safely assume that the fuel efficiency for one mile in a Boeing plane is the same or close to the fuel efficiency for one mile in the air in any plane.

Exhibit 2.5 Average fuel efficiency for one mile in flight

units marked in columns

Model average fuel economy
(gallons / mi) (1)
avg number of
passengers (2)
as a % of total Boeing
planes in service (3)
B-737
1.79
129
37.7%
B-747
6.61
486
4.2%
B-757
2.75
222
34.1%
B-767
2.75
266
15.9%
B-777
5.29
383
8.1%
AVERAGE
2.75
218
 

Alright! Now we're getting somewhere. Based on our assumptions and calculations, one mile in flight burns 2.75 gallons of fuel on average. Plus, we can see that on average one plane can carry 218 passengers.

6. Amount of CO2 produced by one mile in flight

to top | previous step: 5. Average fuel efficiency for one mile in flight | next step: case study

So now we know on average how many gallons of fuel are burned for each mile in the air. Now we're ready to do a little chemistry and see how much CO2 is released when you burn several gallons of fuel.

In a turbine engine, kerosene is mixed with air and combusted. The hot gases created by the combustion reaction in the engine exit the engine at high speeds and create thrust in the opposite direction. This moves the plane forward.

The chemical formula for kerosene is C13H18. It is burned in a typical combustion reaction where atmospheric oxygen (O2) combines with a hydrocarbon (CxHy) to create carbon dioxide (CO2) and water (H2O). This is the same combustion reaction that occurs in our bodies to generate energy from food. Other elements in the air (such as nitrogen and carbon dioxide) are burned in the engine. They create other molecules like nitrates, but they are ignored in our calculations.

Here's our chemical reaction for combusting kerosene: C13H18 + O2 -> CO2 + H2O .

We just need to balance it so that the number of elements that enter our reaction exit our reaction. Unbalanced, the formula has 13 carbon atoms (C), 18 hydrogen atoms (H), and 2 oxygen atoms (O) creating 1 carbon atom, 3 oxygen atoms, and 2 hydrogen atoms. Atoms can't appear or disappear! We need to balance the equation by saying how many molecules of each element enter and exit. We do that by putting coefficients in front of each molecule in our equation that, when multiplied by the number of atoms in the coefficient's associated molecule, create the same number of atoms entering and exiting. Balancing the combustion reaction yields, 2C13H18 + 35O2 -> 26CO2 + 18H2O. 26 carbon atoms, 36 hydrogen atoms, and 70 oxygen atoms combine to create 26 carbon atoms, 36 hydrogen atoms, and 70 oxygen atoms. When you look at the coefficients, our combustion reaction takes in two kerosene molecules for every 26 carbon dioxide molecules it creates. That means for every kerosene molecule, 13 carbon dioxide molecules are created. Scaling up, for every gram of kerosene consumed, 13 grams of carbon dioxide are created.

That's all the chemistry we need. We just need to know the density of kerosene so we can move from a measure of volume like gallons to a measure of mass like grams. The density of kerosene is 0.81762 grams/milliliter or 3,095.25 grams/gallon.

2.75

Gallons of fuel (kerosene) burned each mile(1)

>

8,521.30

Grams of kerosene burned each mile (2)

>

110,776.88

Grams of CO2 produced each mile (3)

>

244.22

Pounds of CO2 produced by one mile in the air (4)

>

1.12

Pounds of CO2 per passenger per mile (5)

  1. This is what we determined in Exhibit 2.5.
  2. 2.75 gallons kerosene / mile * 3,095.25 grams kerosene / gallon
  3. 8,521.30 grams kerosene / mile * 13 grams CO2 / 1 gram kerosene
  4. 110,776.88 grams CO2 / mile * 0.00220462262 pounds/gram
  5. 244.22 pounds CO2 / mile / 218 average passengers per flight

There you have it. To the best of our ability, on average...

one mile in flight creates a little over 1 pound of carbon dioxide per passenger.

Case Study: Babcock Graduate School of Management

to top | previous: 6. Amount of CO2 produced by one mile in flight

At the end of the academic year, students can choose from a number of international trips to learn more about business in other countries. In addition, several student trips to New York and Managua, Nicaragua occur throughout the year. To determine the carbon footprint of all this flying, we first need to figure out the distance between the cities along the route of each student trip. We were given departure and arrival cities by each trip coordinator. We determined typical layovers using popular travel sites, and we calculated the flying distance of each leg using popular tools.

Exhibit A Flying distance of Babcock's student trips

Nautical and statute miles as marked

Student Trip
Distance
(nautical miles)
Distance
(statute miles)
Tokyo, Japan
D: GSO to ORD (Chicago) to TYO
A: TYO to ORD to GSO
 
 
 
GSO to ORD
512
589
ORD to TYO
5,436
6,255
Total
5,948
6,844
 
 
Mumbai, India
D: GSO to ATL to JFK to BOM
A: BOM to DXB (Dubai) to ATL to GSO
 
 
GSO to ATL
266
306
ATL to JFK
659
759
JFK to BOM
6,762
7,782
BOM to DXB
1,039
1,196
DXB to ATL
6,588
7,581
ATL to GSO
266
306
Total
15,581
17,930
 
 
 
Beijing, China
D: GSO to IAD to PEK
A: PEK to SFO to ORD to GSO
 
 
 
GSO to IAD
208
239
IAD to PEK
5,996
6,901
PEK to SFO
5,123
5,895
SFO to ORD
1,599
1,840
ORD to GSO
512
589
Total
13,438
15,464
 
 
 
Managua, Nicaragua
D: GSO to MIA to MGA
A: MGA to MIA to GSO
 
 
GSO to MIA
619
712
MIA to MGA
884
1,017
Total
1,503
1,729
 
 
New York, New York
D: GSO to ATL to JFK
A: JFK to DCA to GSO
 
 
 
GSO to ATL
266
306
ATL to JFK
659
759
JFK to DCA
185
213
DCA to GSO
215
248
Total
1,325
1,525
Source: Lisa Bryant provided student participation figures as well as departure and arrival cities.

Now we know how far each trip is in the air. We just need to know how many students travel on each trip to determine how many total miles Babcock students fly in a year.

Exhibit B Number of student trip participants

Units marked in columns

Student trip Distance (miles) No. students Student-miles
International Trips      
Japan
13,689
21
287,466
India
17,930
14
251,021
China
15,464
24
371,144
Latin America*
11,603
16
185,648
Central Europe*
10,336
57
589,152
TOTAL
69,022
132
1,684,430
 
Nicaragua Trip
December 2007
3,458
16
55,330
March 2008
3,458
18
62,246
TOTAL
6,916
34
117,576
 
New York Trips
BMA
1,525
15
22,880
Finance club
1,525
10
15,254
TOTAL
2,650
25
38,134

With the total number of student-miles, we can put it all together to see how much carbon dioxide is created by Babcock's student trips.

1,840,140

total student-miles from Babcock's student trips

>

1.12

pounds of CO2 per mile per passenger in the air

>

2,063,140

pounds of CO2 from Babcock's flights (1,032 tons)

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