---
title: Airlines Keep Their Grip on the World's Busiest Airports Under 1970s Rules
description: The global airport slot system dates to 1974. Airports say it keeps fares high and blocks new airlines; the carriers say it works. Would reform help?
author: Darie Nani (Editor-in-Chief)
updated: 2026-09-15T11:26:45.968Z
canonical: https://www.sovereignmagazine.com/article/airlines-keep-their-grip-on-the-world-s-busiest-airports-under-1970s-rules
categories: Business
content_type: Analysis
region: Global
publication: Sovereign Magazine
schema_type: Article
---

Getting a plane onto a runway at one of the world's busiest airports at a useful hour depends less on filling the seats than on holding a slot, a permission to land or take off at a set time, and at the most crowded airports those permissions are governed by rules first drawn up in 1974. On 15 September, Airports Council International (ACI) World, the trade body for the world's airports, published a white paper arguing that the system has aged into a barrier that keeps fares high and shuts newer airlines out of the airports travellers most want to use.

Justin Erbacci, ACI World's Director General, put the charge bluntly, saying the industry is trying to run a modern aviation system on rules built for a different era. The paper calls for what ACI describes as a modernised, transparent and collaborative approach to airport access.

> "We are trying to run a 2026 aviation industry on a 1970s operating system."
> — Justin Erbacci, Director General, ACI World

The airlines, through their own trade body, say the current rules work and that hasty change would do more harm than good.

## The System Began as a Voluntary Fix in 1974

In 1974 the industry agreed a voluntary way to manage peak-hour congestion, and over the following decades it became the Worldwide Slot Guidelines, set jointly by IATA, ACI and the Worldwide Airport Coordinators Group. The European Union wrote its version into law in 1993 under Regulation 95/93, giving the arrangement legal teeth on one of the busiest continents for air travel.

Airports fall into three tiers. Level 1 airports have spare capacity and need no slots. Level 2 airports face moderate congestion and rely on voluntary adjustment. Level 3 airports are strictly coordinated, and there every arrival and departure needs an allocated slot. Roughly 200 Level 3 airports worldwide handle close to two-thirds of all passengers, which means fewer than a tenth of the world's airports carry the bulk of the people flying. ACI says 85.5% of those busiest airports are at or near full capacity.

## Grandfather Rights Keep the Same Carriers in Place

The mechanism ACI singles out is the historic right, commonly called the grandfather right. An airline that used a slot in the equivalent season a year earlier automatically keeps it for the next one, provided it clears the 80/20 threshold: use the slot at least 80% of the season or forfeit it. Meet that bar and the slot renews indefinitely, which means an incumbent that arrived decades ago holds its position without having to rebid for it.

ACI argues this locks in the established carriers at the expense of new and smaller ones. It points out that at the 50 most congested airports the four largest carriers control 67% of flights, and that the number of congested or slot-restricted airports has risen by more than a quarter over the past decade while global passenger traffic is projected to nearly double by the mid-2040s. The rule also pushes airlines to fly near-empty flights simply to keep their slots, a practice that drew wide criticism when demand collapsed during the pandemic.

## Heathrow Fares Run Higher Than at Rival Airports

The clearest independent evidence that scarcity costs passengers comes from the UK, where the Civil Aviation Authority found that fares at Heathrow averaged 23% higher than at other London airports and 24% higher than at other European hubs, a gap it attributes to slot scarcity. In its [analysis of slot scarcity and ticket prices](https://www.caa.co.uk/media/mhpbazy1/46-frontier-slot-scarcity-and-ticket-prices-at-heathrow.pdf), the regulator estimated the premium at about £47 on a short-haul ticket and £216 on a long-haul one.

The scarcity premium has made the slots themselves valuable assets. Heathrow has the most active market in the world for them: a prime slot pair sold to Oman Air for $75 million in 2016, and pairs have reached $75 million and above through 2025 and 2026.

## Airlines Say the Rules Already Work

IATA, representing the airlines, argues that the slot system has functioned with great success for decades and that hasty reforms risk creating unintended consequences. Peak-time airports already run at 95% to 98% utilisation, so raising the use-it-or-lose-it threshold is impractical when there is almost no spare capacity to reallocate. In its [position on slot rule reform](https://www.iata.org/en/programs/ops-infra/slots/slot-rule-reform/), IATA says the rules have to balance access for new entrants against the schedule certainty airlines need before they will invest in new routes.

IATA also offers counter-evidence that the system has not frozen competition: over the past decade in Europe the share of routes served by three or more carriers rose by 25%, and easyJet grew from a start-up into one of the largest holders of slots at Europe's primary airports under the current rules. Auctions, peak pricing and algorithmic allocation, on IATA's reading, add cost and uncertainty without delivering better outcomes for passengers.

## Slots Have Concentrated Further Where They Can Be Sold

The case for simply letting airlines trade slots runs into Heathrow's own record. There, slots change hands freely, and the market has still entrenched dominant carriers such as British Airways rather than opened the airport to newcomers.

Independent evidence shows that scarcity raises prices at congested hubs. Whether rewriting the rules would bring those prices down is unproven.

## Regulators in the US and EU Are Taking Another Look

In the United States, the Federal Aviation Administration slot-restricts five high-density airports: JFK, LaGuardia, Reagan National, Newark and Chicago O'Hare. It extended JFK's high-density limits through October 2028, holding the airport to caps of 81 movements an hour at peak. In Europe, the European Commission opened a consultation on its airport slot rules in 2025, inviting feedback on whether the framework still fits the market it governs.

For the traveller, the scarcity premium at hubs such as Heathrow is real and measured. What no one can yet show is whether reworking the 1974 rulebook would pass that saving to passengers, or simply move the most valuable slots from one large carrier to another.

## FAQ

**Q: How are airport slots allocated?**
At coordinated airports, slots are handed out under the Worldwide Slot Guidelines, agreed by IATA, ACI and the Worldwide Airport Coordinators Group and, in the EU, enshrined in law. An independent coordinator allocates each arrival and departure time. In practice most slots renew automatically to the airline that held them the previous equivalent season, with a portion set aside for new entrants.

**Q: What is the 80/20 rule for airport slots?**
The 80/20 rule, also called use-it-or-lose-it, requires an airline to operate a slot at least 80% of the time across a season. Clear that bar and the airline keeps the slot for the next equivalent season. Fall below it, and the slot returns to the pool for reallocation.

**Q: What are Level 3 airports?**
Level 3 is the most restricted category of airport coordination. At a Level 3 airport, congestion is severe enough that every take-off and landing needs a formally allocated slot. Level 1 airports have adequate capacity and need no slots, while Level 2 airports use voluntary adjustment to manage moderate congestion.

**Q: Why are airport slots so valuable?**
At the busiest airports there are far more airlines wanting to fly than there are slots available, so a permission to use the runway at a desirable time becomes a scarce and tradable asset. At Heathrow, where slots can legally be bought and sold, prime pairs have changed hands for $75 million and more.