What are airport slots, and how do they impact your travel plans?

In aviation, there’s one term we often use that carries a lot of weight: slots, and it’s essential for understanding airline and airport operations.

This term is typically reserved for aviation insiders, and you won’t hear it often in casual conversations.

However, when it comes to commercial air travel in the U.S. and globally, slots are incredibly important.

Here’s an example of how it's used in context:

Frontier Airlines recently secured slots at John F. Kennedy International Airport (JFK), enabling the airline to introduce its inaugural nonstop flights from the bustling New York airport.

Slots dictate which airlines can operate from capacity-limited airports, how often they can fly, and sometimes even which routes they can serve.

They play a key role in securing the coveted landing rights at New York’s LaGuardia Airport (LGA) as well as JFK.

Slots are also critical in determining which U.S. airlines and cities have nonstop flights to Tokyo’s Haneda Airport (HND) and which ones can offer transcontinental routes from Ronald Reagan Washington National Airport (DCA).

Currently, slot-related issues are at the heart of a dispute involving Delta Air Lines, Aeromexico, the U.S. Department of Transportation, and the Mexican government. This battle could lead to the dissolution of a joint venture between the two airlines, both of which are part of the SkyTeam alliance.

So, what exactly are slots, and why are they so important?

Here’s a quick overview.

What is a slot, exactly?

A slot is a permit that allows a flight to take off or land at a congested airport. In the U.S., slots are allocated at airports where the Federal Aviation Administration has determined that airline demand exceeds the available capacity for flights.

Without slot regulations in place, these airports would experience such high congestion that flight operations would likely face significant delays.

At its core, a "slot" is the permission to either take off or land at a specific time. Typically, these slots come in pairs, referred to as "slot pairs" in aviation terms, and owning a pair allows an airline to operate one round-trip flight.

Takeoff and landing slots are usually spread throughout the day and week to ensure a smooth flow of air traffic and prevent operational bottlenecks.

Which airports in the U.S. utilize slots?

In the U.S., the FAA strictly manages takeoffs and landings through slot controls at only three airports.

These include:

• LaGuardia Airport (LGA)
• John F. Kennedy International Airport (JFK)
• Ronald Reagan Washington National Airport (DCA)

In addition, there are four more airports where the FAA enforces lighter regulations. While these airports don't follow a formal slot system, the FAA still requires close coordination with airlines to manage takeoffs and landings. These airports are:

• Chicago O'Hare International Airport (ORD)
• Los Angeles International Airport (LAX)
• Newark Liberty International Airport (EWR)
• San Francisco International Airport (SFO)

How are airport slots allocated?

It’s a complex process.

Slots are generally assigned by the Department of Transportation (DOT), often after a competitive application process, and are regulated by the Federal Aviation Administration (FAA).

In certain situations, airlines apply directly to the federal government, and the DOT assesses and distributes the slots based on factors such as consumer benefit, competition between airlines, and improved connectivity for travelers.

Slots can become available when an airline is required to relinquish one or more pairs due to antitrust issues or if it hasn’t been fully utilizing its slots, among other possible reasons.

Historically, slots have been transferred between airlines, leased to other carriers, or pooled and shared as part of significant business deals.

In a notable case from the early 2020s, American Airlines leased several LaGuardia slots to JetBlue as part of their ill-fated Northeast Alliance. This arrangement was eventually reversed after a federal judge blocked the alliance on antitrust grounds.

Slots are highly sought after and incredibly valuable.

The need for slots arises from scarcity. There’s a limited number of runways and available time at high-demand airports.

Think of a slot as an airline's "pass" to access one of these busy airports.

While the true market value of a slot remains somewhat elusive (though some deals have been reported over time), slots are often used as a form of trade or barter between airlines.

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Historically, slots follow a 'use it or lose it' policy, though there are exceptions.

In general, slots operate on a 'use it or lose it' basis.

Airlines typically need to operate the flight they’re assigned a slot for in order to retain it.

If airlines fail to meet specific slot usage thresholds, they risk losing their slots. This prevents carriers from stockpiling unused slots just to block competitors.

The FAA does have the authority to relax slot usage rules. For example, the agency has eased the use-it-or-lose-it policy in the New York area to help alleviate pressure on overburdened air traffic control facilities.

Perimeter regulations

At two major East Coast airports, there are additional restrictions on the types of flights airlines are allowed to operate.

LaGuardia Airport

In New York, alongside LaGuardia’s slot rules, the airport is subject to a 1,500-mile "perimeter" rule imposed by the Port Authority of New York and New Jersey, which oversees the area's main airports. This regulation prevents flights to airports located more than 1,500 miles from LaGuardia.

LaGuardia’s perimeter restrictions are distinct from the slot rules and include two key exceptions. Flights to Denver International Airport (DEN) are allowed to bypass the perimeter limit.

Additionally, perimeter rules (and slots) don’t apply on Saturdays — a typically lower-demand day. In the past, airlines have taken advantage of this by offering certain flights to more distant destinations exclusively on Saturdays.

Ronald Reagan Washington National Airport

In the Washington, D.C. area, airlines at Reagan are generally prohibited from operating flights that exceed 1,250 miles.

However, Congress has granted numerous exceptions, allowing airlines to operate flights beyond the perimeter. Just this spring, lawmakers approved five additional daily round-trip flights as part of the FAA reauthorization bill, with several airlines requesting new routes or increased frequencies under the new exemptions.

These exceptions have often faced strong opposition from regional lawmakers and the airport’s governing authorities. They have also been politically charged, sometimes pushed through with the help of Congressional leaders who sought new routes connecting their home states.

Why so few long-haul flights?: What is the reasoning behind Washington's Reagan National Airport's 'perimeter'?

International slot negotiations

The DOT has also found itself involved in slot-related discussions at international airports.

The department is responsible for deciding which U.S. airlines and cities are granted flights to Tokyo’s slot-restricted Haneda Airport (HND). A recent slot opening at HND ignited intense competition among U.S. airlines, culminating in American Airlines launching new service from JFK to HND.

Alleged anticompetitive behavior at Mexico City International Airport (MEX) recently led the DOT to disrupt Delta’s close partnership with Aeromexico. The airlines are challenging a recent order from the Biden administration to dissolve their joint venture.

Slots at other airports

Beyond the four airports subject to federal slot regulations, individual airports can set their own slot rules for reasons such as terminal capacity or noise control. For example, John Wayne Airport (SNA) and Long Beach Airport (LGB) in California have implemented slot controls due to concerns about noise and overcrowding.

Similar restrictions have been applied at international airports where nighttime flight bans are in effect.

Next time you fly through a busy airport, take a moment to appreciate the extensive behind-the-scenes coordination that allows your airline to operate there — or even maintain its spot at the gate.