Putting planes in the sky – slot management explained

Sydney Airport CEO Scott Charlton discusses slot management with Neil Garwood, CEO of Airport Coordination Limited. Pic: Lisa Dieu

Airport slot managers play a crucial role in planning for the smooth passage of aircraft and passengers through the world’s major airports every day – always there, behind the scenes, ensuring maximum airport traffic with minimum fuss.

But it’s our experience that most people – even some in the industry – don’t understand what slot management is and why it’s so important to global aviation. With that in mind, we’ve prepared this ‘explainer’ on what slot management is and how it works.

What is slot management?

Slot management is part art, part science, it’s the allocation of airport capacity in the form of take-off and landing slots to airlines, enabling them to use crucial airport infrastructure such as boarding gates and passenger airbridges.

Why is it so important?

Slot management balances supply and demand, facilitating the most efficient use of airport capacity. Without slot management, airlines may all choose to arrive or depart at the same time causing unacceptable congestion or delays to passengers. Where demand is high, slot management helps to spread it to a level that the airport’s infrastructure can accept, and it can help control environmental limits such as curfews and hourly movement limits too.

How do slot managers work?

Slot managers such as Airport Coordination Limited (ACL) are independent arbiters who work with airports and airlines to ensure fair allocation of capacity. Without a slot manager all the peak slots could be dominated by one airline, or the airport could decide to restrict certain airlines from operating.

When did it start? A brief history

The first global slot guidelines were introduced in the 1970s in response to growing demand for air travel often exceeding the usable capacity at some airports, causing operational and fairness issues. Slot managers were introduced to ensure independence and neutrality, attributes which exist to this day, ensuring that slots are managed fairly and transparently, giving certainty to passengers and enabling optimal use of airport infrastructure.

What is the 80:20 rule?

The ‘80:20 rule’ is the global benchmark for slot management. Slots are allocated every six months for the so-called summer and winter seasons and an airline must use their allocated slots at least 80% of the time to ensure they retain them at that particular airport for the next equivalent season. Either use it or lose it. This means routes can be developed and sustained over time and optimises slot utilisation, reducing waste.

How do airlines get slots?

They ask the slot manager for them, nominating days and preferred flight times. For busy urban airports like Sydney, where ACL has managed the slots since April 2025, morning and evening slots are in highest demand for business travel. If capacity is available, they will be allocated the slot. If demand exceeds supply at the requested date and time the slot manager will try to find an alternative. The airline can also join a waiting list, with the opportunity to be allocated the slot when capacity becomes available.

Who makes the final decision on slot allocation?

Slot managers make the final decision on slot allocation based on what is fairest and best for all parties in line with local regulations.

Can slots be bought and sold?

Slots can be worth huge amounts of money at airports that allowed them to be traded. In 2016, for example Oman Air paid Air France-KLM $US75 million for a slot pair at Heathrow Airport. However, not all airports, including Sydney, allow incumbent airlines to sell their slots.

Do airlines game the system?

They sometimes try. Like any set of rules, practices can evolve that might be considered outside the original spirit. It’s the job of regulators and slot managers to ensure that the best use of capacity is met, and that the system remains fair and accessible for all.

Tricks of the trade

For a good slot manager, it boils down to being three things: proactive, solutions-focussed, and pragmatic. For airports, the slot manager will advise them to “trust the process” – the system works to optimise the allocation of capacity. And for airlines that want slots at constrained airports: stay on the waiting list and submit your applications on time!

Enforcement

As with any ‘carrot’, having a ‘stick’ can also help. In the slots world this takes the form of monitoring, where the slot manager will review how airlines use the allocated slot and pick up on any potential misdemeanours or poor performances. The intention is collaborative improvement, however in some cases penalties can apply and even the loss of an airline’s slots in extreme cases.

Tech advances

In the earliest days, slots were recorded on paper in huge notebooks that set out the season line-by-line. Nowadays slot managers use advanced systems to record who holds what and how slots are being used. And in many cases, airlines can ‘self-serve’ to test the operating environment before applying. Increased automation will help slot managers to become even more efficient, but the system will always rely on people skills and collaboration to get the best from constrained airport infrastructure.

About ACL: ACL is the world’s leading independent airport slot manager. Founded in 1991, the company operates in 12 countries serving 78 airports ranging from international hubs with constrained capacity to smaller regional airports seeking to develop their networks. Around five million aircraft movements are successfully coordinated or facilitated by ACL each year, carrying over 700 million passengers. The company has offices in London, Dubai, Auckland and Sydney.