You must have come across this before. Sitting in your seat, waiting for your flight to depart when the pilot comes on and makes an announcement. “We’ve missed our slot, so we’ll be delayed further” – one guaranteed to elicit groans from the passengers.

In the arcane world of aviation, a slot is a very important thing for an airline to have. In fact, airlines have spent up to US$75 million on slots at airports such as London Heathrow. What are they and why are they so valuable in certain places?

What Is A Slot?

Very busy airports are referred to as Level 3. These are where demand for infrastructure exceeds capacity so much so that airlines need to apply for a slots in advance in order to use the facilities. Slot conferences are held months in advance of your flight to sort all of this out.

The International Air Transport Association (IATA) defines an airport slot as “a permission given by a coordinator for a planned operation to use the full range of airport infrastructure necessary to arrive or depart at a Level 3 airport on a specific date and time.”

That means that an aircraft is expected to use the slot time given and the flight will be scheduled accordingly to make that time. What happens when a service is delayed though?

This is what is being referred to by the pilots when they say they’ve missed their slot. As one or both of the airports you’ll be using is Level 3, you need to wait until there is space for your flight to fit into the sequence before you can leave.

Overall Thoughts

Many airports around the world are Level 3 slot controlled. Some are like this all year round, while some will be at this level only during their particular high season, summer or winter. Usually the only way to move down to Level 2 or Level 1 is for more facilities to be built.

The next time you’re delayed and wondering why you’re waiting even longer due to slots, you will now know what that means. In the complex dance of air traffic management, they are extremely important.

Did you know all about slots before? Thank you for reading and if you have any comments or questions, please leave them below.

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Featured image by Robert Bye on Unsplash.
London Heathrow image by Kenneth Iwelumo via