Cargo vs. Passengers

luggageOnce total emissions for a flight are known, emissions per passenger can be calculated. It is important to note that calculators differ in how they take into account cargo versus passenger load, seat occupancy rate, and seat class.

The majority of a flight’s total weight is the aircraft itself and the fuel it carries. Flight crew, crew luggage, steward’s supplies, etc. are all considered part of aircraft weight. ‘Payload’ is defined as the weight of the people and items that are being transported, including passengers, their luggage, and cargo. An industry-wide standard of 220 lbs (100kg) is assumed for each passenger and their luggage. (According to industry experts, this estimate might be lower than the actual average weight of a passenger and their luggage.)


Two Examples of Aircraft, Fuel and Payload Weight

Airplane Type:

 

A 300-600

A 320

(in metric tons)

percentage of max. takeoff weight

(in metric tons)

percentage of max. takeoff weight

Maximum takeoff weight

171.7

100%

73.5

100%

Maximum zero fuel weight

130

75.7%

61

83%

Maximum fuel capacity

55

32.2%

19

26.3%

Typical operating weight empty

90.9

52.9%

42.4

57.7%

Maximum payload

34.9

20.3%

16.6

22.6%

Estimated total maximum passenger weight in single class configuration

298 passengers x 100kg = 29.8

17.4%

164 passengers x 100kg = 16.4

22.3%

(Source: Airbus)

Passenger airplanes usually carry additional cargo. Cargo consists of freight and mail. Thus, cargo should be allocated some of the GHG emissions associated with the flight. There are several ways that this cargo can be accounted for in an air travel emissions calculator. Two such approaches are described below:

1. The responsibility for the airplane travel lies with the passengers.

This approach assumes that the airplane flies because of the passengers and not because of the freight. The calculator therefore only subtracts the emissions associated with marginal increase in fuel consumption caused by the weight of the cargo: the increase in fuel burn due to the extra cargo is divided by the number of passengers and subtracted from each traveler’s carbon footprint. Note that this increase in fuel burn is low because most of the weight of the airplane is its airframe and the fuel it transports.

2. The responsibility for the air travel lies proportionally with the passengers and with the cargo.

Total emissions are assigned to cargo and passengers based on their percentage of total cargo weight. For example, if 80% of the payload weight is passengers and luggage and 20% is cargo, then 20% of total flight emissions are subtracted from the passengers’ carbon footprint.

Both of these approaches are valid, although the authors argue that if the cargo cannot be shipped with a particular passenger flight, it would be shipped in another passenger flight or in a cargo flight. Also, revenues from cargo are a significant source of income for most large passenger carriers. Because of this, the authors find the second approach more appropriate.

Points of Discussion:

How are cargo, fuel weight, and number of passengers correlated?

Flight distance may be strongly correlated with the amount of cargo on a flight. Long distance flights require more fuel storage and the weight of this additional fuel would limit the amount of cargo taken on board, as a plane cannot exceed its maximum takeoff weight. Fuel storage requirements could also eliminate the capacity for cargo on certain flights.

How does additional fuel weight on very long distance flights (or because of tankering) impact cargo? In other words, how large are the differences in the amount of cargo that airlines report for each airplane type (i.e. what is the variance)?

If you have suggestions, comments or insights about these topics, please email offsetreview@sei-us.org