Aircraft hours are the total number of aircraft block hours in revenue service, block hours being calculated from the moment it moves under its own power for purpose of flight until it comes to rest at the next point of landing

Aircraft kilometres are the sum of the product obtained by multiplying the number of flights performed on each flight stage by the stage distance

Aircraft utilisation is the average number of block hours that each aircraft is in use. This is generally measured on a daily or annual basis

Available seat kilometres (ASKs) are obtained by multiplying the number of seats available for sale on each flight stage by flight stage distance

Available tonne kilometres (ATKs) are obtained by multiplying the number of tonnes (2,204 lb) of capacity available for carriage of passengers and cargo on each sector of a flight by flight stage distance

Average aircraft capacity is obtained by dividing available tonne kilometres by aircraft kilometres flown (or available seat-kms by aircraft kms flown)

Average passenger haul is obtained by dividing revenue passenger kilometres flown by the number of passengers

Average stage length is obtained by dividing aircraft kilometres flown by number of aircraft departures for each airline; it is the weighted average of stage/sector lengths flown by an airline (normally the great circle distances)

Block time (hours) is the time for each flight stage or sector, measured from when the aircraft leaves the airport gate or stand (chocks off) to when it arrives on the gate or stand at the destination airport (chocks on)

Break-even load factor (%) is the load factor required to equate total traffic revenue with operating costs

Code sharing is the use of the designation code of one or more airlines on a flight operated by another airline

Co-ordinated airport is an airport where an independent co-ordinator has been appointed to facilitate the allocation of take-off and landing slots (times) to airlines at congested airports in Europe

Flying time (hours) is the time for each flight stage or sector, measured from when the aircraft leaves the ground or lifts off to when it touches down on the runway on arrival at the destination airport

Grandfather rights is the convention by which airlines retain the right to take-off and landing slot times at an airport as long as they are used (also used in conjunction with route rights)

Interlining is the acceptance by one airline of travel documents issued by another airline for carriage on the service of the first airline, according to conditions laid down in an interline agreement (which include the allocations of revenues between the two carriers); an interline passenger is one using a through fare for a journey involving two or more separate flights and two or more carriers

Operating costs per ATK is a measure obtained by dividing the total operating costs by ATKs. It includes flight operating expenses, sales ticketing and promotional costs, ground operations costs and general and administrations costs. It usually excludes interest payments, but includes aircraft lease rentals

Operating ratio (%) is the operating revenue expressed as a percentage of operating costs

Passengers carried are obtained by counting each passenger on a particular flight (with one flight number) once only and not repeatedly on each individual stage of that flight (or one ticket coupon equals one passenger), with a single exception that a passenger flying on both the international and domestic stages of the same flight should be counted as both a domestic and a international passenger

Passenger load factor (%) is passenger-kilometres expressed as a percentage of available seat kilometres (on a single sector, this is simplified to the number of passengers carried as a % seats available for sale)

Punctuality is measured as the percentage of flights departing within 15 minutes of schedule, according to the most widely used airline industry standard

Regularity is the percentage of flights completed to flights scheduled, excluding flights cancelled for commercial reasons

Revenue passenger refers to passengers paying 25% or more of the normal applicable fare (for ICAO statistical purposes)

Revenue passenger kilometres (RPKs) are obtained by multiplying the number of fare paying passengers on each flight stage by flight stage distance

Revenue tonne kilometres (RTKs) are obtained by multiplying the total number of tonnes of passengers and cargo carried on each flight stage by flight stage distance. Passengers tonnekilometres are normally calculated on a standard basis of 90 kg average weight, including free and excess baggage, although this has been increased recently by some airlines (eg British Airways have recently increased the average passengers weight from 75kg to 80kg, as a result of CAA directive, to which the 20 kg free baggage allowance should be added)

Seat factor or passenger load factor on a single sector is obtained by expressing the passengers carried as a % of the seats available for sale; on a network of routes it is obtained by expressing the total passengers-kms as a % of the total seat-kms available

Seat pitch is the standard way of measuring seat density on an aircraft. It is the distance between the back of one seat and the same point on the back of the seat in front

Scheduled freight yields are obtained by dividing total revenue from scheduled freight by RTK from freight

Scheduled passenger yields are obtained by dividing the total scheduled passenger revenue by RTK from passengers

Scheduled services are services provided by flights scheduled and performed for remuneration according to a published timetable, or so regular or frequent as to constitute a recognisably systematic series, which are open to direct booking by members of the public; also extra revenue flights occasioned by overflow traffic from scheduled flights; and preliminary revenue flights on planned new air services

Slot at an airport is the right to operate one take-off or landing at that airport within a fixed time period. In practice, the slot timings are only nominal and flights often take off and land at times outside their specified slot period, although airlines must possess the nominal slots to operate air services. Slots are traded between airlines legally in the US, and unofficially in other parts of the world (where only the exchange of slots is officially permitted)

Unduplicated route kilometres are the lengths in kilometres of all the flight stages operated by the airline, each counted only once, and regardless of frequency or direction

Unit costs are obtained by dividing total operating costs by ATKs

Weight load factor is revenue tonne kilometres performed expressed as percentage of available tonne kilometres (also called overall load factor)

Wide-bodied aircraft are civil aircraft which have two passenger aisles in normal configuration (eg B767); narrow-bodied aircraft, such as the B757 have only one aisle

Yields are obtained by dividing the total operating revenue by RTKs (or sometimes by ATK); passenger yields are obtained by dividing passenger revenues by RPKs, and cargo yields by dividing cargo revenues by FTKs. Revenues have historically been recorded before the deduction of travel agent commissions, giving gross rather than yields net of commissions