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Airport slots
At the world’s busiest airports, airlines can’t simply decide to fly. They need a slot: permission to land or take off at a set time. Slots are scarce, so they can be worth millions.
Why slots exist
A runway can only handle so many flights an hour. At most airports there’s spare room, but at a few the flights airlines want are far more than the runways, terminals or stands can take, especially in the morning and evening peaks.
Three levels of airport
Under IATA’s Worldwide Airport Slot Guidelines, airports fall into three levels:
- Level 1Not congested. Airlines schedule freely.
- Level 2Schedules facilitated: busy at times, so a facilitator adjusts timings by agreement.
- Level 3Coordinated: an independent coordinator allocates slots, and a flight can’t operate without one.
Level 3 airports are a minority, but they’re the big ones: IATA says some 43% of all passengers use a slot-constrained, Level 3 airport.
Use it or lose it
Slots are allocated per season, summer and winter, as a series: the same time on the same day each week. An airline that operates a series at least 80% of the time keeps it for the next equivalent season. This is the 80/20 rule, and the right to keep a series is called historic precedence (or, informally, grandfather rights).
Slots no one holds go into a pool, and part of it is set aside for new entrants, so new airlines have a way in.
Why they can cost millions
Because historic slots stay with the airline that uses them, the only way into a full airport is often to buy or swap slots with another airline, where that’s allowed. At London Heathrow, Oman Air reportedly paid $75 million for a pair of morning arrival and departure slots in 2016.
See how busy airports are built: runways, length and layout, drawn to scale.
London Heathrow’s runwaysSources: IATA, “The dangers of slot auctions” (passenger share, 80/20 rule); Aviation Week, April 2016 (Oman Air). The three levels are defined in IATA’s Worldwide Airport Slot Guidelines.