Aircraft Type

planeThe aircraft fleets of most countries are dominated by aircraft produced by two major manufacturers: Boeing and Airbus. Fuel consumption varies considerably by aircraft model and engine type.

To illustrate how the weight of an airplane and its payload are distributed, the fuel burn rates of three aircraft flying between New York (JFK) and Los Angeles (LAX) are compared in the table below. The table also shows the typical numbers of seats (three class configuration) and fuel burn rate per passenger. Fuel burn rate per passenger is calculated as total fuel burned divided by total number of seats.

Examples of Different Aircraft Types' Fuel Burn Rate

Aircraft

Fuel burned (kg of fuel)

Number of seats

Fuel burned per passenger (kg of fuel)

A320

11,608 kg

150

77.4 kg

B767-300ER

21,445 kg

218

98.4 kg

B747-400

42,920 kg

416

102.4 kg

(Source: Gillespie, TRX Travel Analytics 2007)

This example does not take into account different seat classes or the occupancy rate of an individual flight, which is not always 100%. The Bureau of Transportation Statistics indicates that the current average load factor of flights in the US is about 80%, and has been increasing in recent years (see section on occupancy rates).

The table shows that the fuel burn rate per passenger is a third higher for the B747 than the A320, illustrating the differences among airplane models. The example does not take engine type into account. Engine type can also influence efficiency considerably.

Aircraft fuel efficiency, through weight reduction and progress in aerodynamics and engine design, has steadily improved over the last few decades. Yet there is considerable lag time between technology development and implementation. The total time span between preliminary technology development and the retirement of an aircraft averages 45 to 65 years (IPCC, 1999). Fuel consumption considerations are a priority for airlines because profit margins are narrow and the price of fuel has steadily increased at a time when airfares have been decreasing in response to competition. While many airlines are moving to acquire newer, more fuel-efficient aircraft or to modify their aircraft to increase fuel efficiency, a substantial number of older, less fuel-efficient aircraft remain in service due to the long service lives of passenger aircraft (approximately 30 years).

Points of Discussion:

Calculating emissions by specifying airplane type is not simple. Below we elaborate on several factors that make it difficult to accurately calculate emissions for a specific flight:

Does increased specificity of aircraft type lead to increased accuracy in emission calculators?

Can calculators collect sufficient data to allow for airline-specific calculations that would lead to a ranking of airlines?


Here are some points (of contention) to consider:

  • Current data sets do not calculate the fuel used by each specific aircraft, but estimate fuel consumption of a "representative aircraft" from within an aircraft family. For example, fuel consumption data may be available for the B737 aircraft family, but the actual consumption rates of fuel for aircraft within the B737 family (B737-400 or B737-200) may differ. With this in mind, it would be difficult to accurately rank airlines in an emission calculator.

On the other hand, it may be that the difference in fuel consumption between airplane families greatly outweighs the difference between aircraft within an airplane family. Because of the disparity in scale, data on specific aircraft within a family might be less important and airline ranking would be relevant.

  • Other important factors that affect fuel burn rates, but may not be included into emission calculators include:
    • Engine type
    • Aircraft maintenance
    • Adapted fuel capacity
    • Design modification (e.g. to body or wings)
    • Tankering (Tankering is the common practice of filling fuel tanks at an airport which offers the lowest fuel prices and carrying this fuel for a series of flights - the most environmentally efficient method would be to upload purely the fuel required for the next flight.)

Do these factors play a larger role in determining fuel consumption and subsequent emissions than any specificity regarding aircraft type would reveal?

  • Specifying aircraft type in emission calculators could possibly be misleading, as a traveler cannot be sure what aircraft they will travel on until they are actually on board. Due to code sharing or re-fleeting, the aircraft used for a specific flight may be switched. However, there are several reasons airlines prefer to use scheduled equipment::
    • The flight crew assigned to the original equipment may not be certified to operate a different type of aircraft,
    • The flight schedules are optimized for many factors, including fuel usage. Changing the equipment type will likely sub-optimize the operating costs of the flight, and
    • By using the same type of aircraft the airline avoids having to re-assign all the passengers to a new seating configuration.

    Therefore, we confidently assert that the scheduled aircraft type very closely matches the actual type of aircraft used.

Questions remain as to how to incorporate these factors into emission calculators, and whether doing so would result in a significant increase in accuracy or not. How much do fuel rates vary between a specific aircraft and its "representative family aircraft" (e.g. a Boeing 747-400 and Boeing 747-200)? In other words, does available data allow for airline-specific emissions calculation or are the above mentioned factors significant enough to offset any gained accuracy from calculations based on more detailed information? How often are aircraft switched out on short notice? Are there differences between US, Europe, and Asia regulations regarding these factors?

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

What is Code Sharing?
Code sharing is a practice that allows airlines to extend their reach into cities or routes beyond those they actually serve. Originally, code sharing was deployed to link regional feeder carriers to a larger airline. Code sharing allowed airlines like United to say it served smaller cities like Appleton, Wis., or Fort Wayne, Ind., from its Chicago hub, when the real airline operating those flights was little Air Wisconsin. Eventually, code sharing grew to include marketing agreements between larger airlines. For example, United flight 3099, between Minneapolis and Charlotte is actually operated by US Airways as flight 295, and Delta flight 7619 between Boston and Milan is actually operated by Alitalia as flight 619. The Department of Transportation maintains a list of international code-sharing agreements on its website, but there is no regulation or guide to code sharing on domestic flights. (Taken from David Grossman, USA Today, 1/23/2006)