Q: How does the airline industry measure its volume of business?
Airline payload, in other words revenue-earning traffic, essentially consists of passengers, freight and mail.
Passenger traffic is measured in passenger boardings, or more commonly passenger-kilometres, which are calculated by multiplying the number of passengers by the distance each one flies. This statistic is normally referred to as Revenue Passenger-Kilometres, or RPK, since non-revenue traffic, for example airline staff travelling on duty, is not included.
Freight and mail traffic, similarly, may be measured in tonnes, but more usually tonne-kilometres. Freight and mail together constitute cargo, which is sometimes presented as a single statistic.
The entire payload may be expressed as Revenue Tonne-Kilometres by multiplying the number of passengers by a notional weight (which includes their baggage) and adding it to the cargo traffic before making the distance calculation.
Passenger capacity is normally measured either as Available Seat-Kilometres (ASK), calculated by multiplying the number of saleable seats by the sector distance. An aircraft’s overall carrying capacity is measured in Available Tonne-Kilometres. It is not normal practice to measure cargo capacity because this will vary from flight to flight depending on the passenger load. It is also very sensitive to cargo density – passenger aircraft will normally run out of cargo space before they reach their weight limits.
The relationship between traffic and capacity is called load factor and is of critical importance to airlines.