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Slots – (One Of) The Airline’s Most Precious Assets Explained!

Slots – (One of) the Airline’s Most Precious Assets Explained!

Aviation slots – simply explained! Hello dear readers. After visiting the Airbus factory in my last post, it’s time for some aviation theory again. I hope, that you are in for a good and tasty dose of aeronautical knowledge. Today, I deal with a topic which is often referred to as the gold of aviation. Slots! 

Slots – Time Frames for Airlines!

So-called slots are an instrument (in addition to, for example, air traffic control) to organize the air spaces around the globe and to protect crowded airports from the ultimate chaos in times of ever-growing air traffic

Slots were introduced to ration out scarce infrastructures in aviation. Such scarce infrastructures are, for instance, runways on the ground and airways in the air. There are exactly two types of slots in the world of aviation. The airport and the airway slot.

The Airport Slot

Let us begin with the airport slot. The airport slot simply is a time window in which an airline may use a particular airport to land or take off. These slots are always distributed before a certain flight plan period (Winter/Summer, six months each). 

How many slots a particular airport can allocate depends on various factors. Examples of this are the number of runways available, the terminal capacity or a possible ban on night flights. 

A typical way to determine the exact number of possible movements per hour is to look at the so-called most constraining factor of the airport. This most constraining factor is the runway system at many airports: 

  • Do the runways cross or do they run parallel to each other? A parallel runway system allows for significantly more movements per hour
  • How far away are those runways from each other? 
  • Hence, can landings and take-offs be performed independently on those runways at the same time? 

Of course, many other things could be constraining factors, such as the topography surrounding the airport, the number of available taxiways, or even the usual weather conditions.

Airport slots become necessary when the demand for flight movements exceeds the supply! Easy as that. Just imagine a football stadium with 80,000 available seats. All is fine if 79,000 are interested in a ticket for the big game. But what if 89,000 people want to watch the match? We need to coordinate and allocate the available capacity. 

In Europe, airports with lass capacity than demand are “slot-restricted”. The allocation of slots is coordinated at such airports, for example in London Heathrow or Paris Charles de Gaulle. In Germany Frankfurt am Main, Munich, Düsseldorf, Berlin Tegel and Schönefeld, Stuttgart and Hamburg are coordinated

Frankfurt Airport slots
Frankfurt Airport is one of the German “slot-coordinated” airports

Airport slots – a scarce and sought-after commodity!

Let me quickly explain, how this coordination works in Germany, my home country. In Germany, airport slots are allocated on a seasonal basis by so-called “slot coordinators” who are appointed by the state. 

If an airline wants to serve an airport daily a series of 14 slots is necessary, one slot for arrival and one for the departure on each day of the week. If an airline receives a slot, it can swap it with another in the same ratio – but not sell it!

This is quite different at London Heathrow Airport. Here, the most desired slots in the peak hours (typically in the morning and evening when business people want to travel) went “over the counter” for high seven- or even eight-digit prices.

Slots – Grandfather Rights!

Of course, slots are not thrown into a bag and simply distributed to a new airline after a flight plan period. If the airline uses a slot(series) at least 80% of the time, it has the privilege to also use it in the subsequent season. This is called “grandfather right”.

The airport slots, therefore, play an essential role in the network planning of the airlines. That is due to the fact, that without these slots, the corresponding airports cannot be served at the desired time. This may be a bit less significant for holiday carriers, of course. Business airlines, however, need to offer attractive flight times to their clientele. Ideally, a busy businessman or businesswoman can arrive at the destination in the morning to have the full working day available and leave again in the evening.

Incidentally, the IATA Slot Conference takes place every six months. This conference is intended to provide a forum for the allocation of slots and to facilitate a consensus between all stakeholders. 

You can now imagine that slots at airports are a quite important and sensible field in aviation. If all available slots are allocated at an airport, it can become quite busy. Have a look:

The Airway Slot

Let’s get airborne again and deal with the second type of slots: The airway slot. Sometimes not only airports but also air spaces are overloaded. There can be many different reasons for this. Many of them are rather uncomfortable. These include thunderstorms or storms that need to be avoided or volcanoes that spontaneously decide to erupt and partially paralyze European airspace.

If such an overload occurs (or is foreseeable), the Directorate Network Management (DNM), namely the air traffic flow management unit of EUROCONTROL (European Air Traffic Control Authority) in Brussels, can impose the so-called airways slots. 

These slots assign small time slots of 15 minutes to planes in which they can commence their flight. Of course, the airline can also request an earlier slot or EUROCONTROL offers one. With the involvement of the airlines, efforts are actively being made to reduce any delays to a minimum.

The fact that this allocation takes place on the ground, with the aircraft not yet airborne, also prevents planes from wasting time in the air unnecessarily and burning kerosene. That makes sense both economically and ecologically.

I hope, you enjoyed the read. If so, feel free to subscribe to my newsletter. You can also find me on Facebook and InstagramMy free aircraft wallpapers are available here!

Also, feel free to browse my other “aviation know-how” articles!

Happy Landings,


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