Rankings / Glossary
Airline efficiency glossary
These terms explain the units and choices used in our methodology. The data download uses the same definitions.
Passenger-miles
Distance travelled by paying passengers, added across flight segments. Multiply passengers by the miles flown on each segment, then add the results. This site uses revenue passenger-miles.
Revenue passenger-miles (RPM)
The passenger-distance measure for travellers carried for payment. RPM is the traffic measure used in the passenger-miles per gallon calculation.
Available seat-miles (ASM)
Seats offered for passenger use multiplied by segment miles, added across flights. Empty seats count, so ASM measures capacity rather than passengers carried.
Seat-miles
The capacity measure called available seat-miles in the source data. A seat flown over a mile contributes a seat-mile whether occupied or empty.
Passenger-miles per gallon
Revenue passenger-miles divided by US gallons of jet fuel used for scheduled passenger service. More passenger-miles per gallon means less fuel per passenger over the same distance.
Seat-miles per gallon
Available seat-miles divided by US gallons of jet fuel. This measures fuel use against offered capacity, without adjusting for how full flights were.
Load factor
Revenue passenger-miles divided by available seat-miles. This distance-weighted share of capacity filled by paying passengers links the seat and passenger efficiency measures.
Regional partner
An airline operating flights sold under another airline's network name. On this site its traffic and fuel are allocated to that network; the split is an estimate where the operator serves several networks.
Mainline
The airline's own operation, separate from flights operated by regional partners. A network total here combines its mainline flying with allocated regional flying.
Airborne hours
Time from leaving the ground to touching down. Aircraft fuel burn per hour on this site uses airborne hours as the denominator, even though the fuel total also includes taxiing and holding.
Block hours
Ramp-to-ramp operating time, including taxiing as well as time in the air. This differs from airborne hours and isn't the denominator used on the aircraft fuel-burn pages.
Flight segment
A flight stage between airports. A connecting journey has separate segments; traffic totals count the passengers and distance on each stage.
Scheduled passenger service
Passenger flying operated to published schedules. This site keeps that service and excludes charter and cargo-only flying when matching fuel with traffic.
CO2 per passenger-mile
Jet fuel gallons multiplied by the EPA jet-fuel CO2 factor, divided by revenue passenger-miles. It counts CO2 from burning fuel; the methodology lists the other warming effects left out.
Emission factor
A conversion from an activity, such as burning fuel or driving a vehicle-mile, into emissions. This site uses the EPA factors specified in the methodology.
Uncertainty range
The span between results from this site's alternative regional allocation methods. It shows sensitivity to that allocation, rather than a statistical confidence interval.
Compare aircraft types and manufacturers, or read the regional profiles. For a definition that needs correcting, see the corrections policy or contact us.