Seat Occupancy Rate (Passenger Load Factor)
Once 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.
Not all flights are fully occupied. Seat occupancy rate (also called passenger load factor) is the ratio of passengers to available seats on board a given flight.
The overall weight of a passenger aircraft is determined primarily by the airframe and amount of fuel carried. Therefore the number of passengers on board has a smaller impact on total fuel consumption. Aircraft use less fuel per passenger the more passengers there are on board. The Royal Commission on Environmental Pollution uses the following example to illustrate this: with an occupancy rate of 51%, the fuel burned per passenger-km is 0.176 lb. In comparison, a load factor of 100% corresponds to fuel burned per passenger-km of only 0.112 lb (RCEP, 2003).
Occupancy rates have fluctuated significantly over the last two decades. In the 1990s, the average load factor was around 65% (ppt). According to the Bureau of Transportation Statistics, average load factor was 77.2% in 2005, increased to 79.2% in 2006, and further rose to 80.3% by November 2007. These fluctuating occupancy rates show the need for regularly updated figures to increase the accuracy of air travel carbon emissions calculators.
Ideally occupancy data would be available by route and not just by air carrier. Such data is to our knowledge not available to date.