By the meteorological calendar, the official start of summer is 1 June. In astronomical terms, the date is 21 June. In the world of airport slot allocation, summer - more specifically, the IATA Northern Hemisphere summer scheduling season - began on Sunday, 31 March 2025. At co-ordinated airports, this date marks the changeover from winter to summer schedules by reference to earlier allocation of airport slots. In the UK, airport slot reform is on table, bringing the potential for turbulence for some airlines and smoother skies for others in future airport slot scheduling seasons.
Slot allocation under the lens
In 2018, the Conservative Government earmarked the UK's airport slots system as ripe for reform [1]. The existing system is set out in legislation (Council Regulation (EEC) No 95/93 as transposed into UK law by the Airports Slot Allocation Regulations 2006) and in turn based on the guiding principles of IATA’s Worldwide Slot Guidelines. Post Brexit, in its May 2023 policy paper "Smarter Regulation to Grow the Economy" the Government advised of the application of a "…scrupulous lens to wider regulations that have accumulated over time so that they are fit for purpose and of benefit to the UK." Airport slot allocation regulations fell under that lens.
In December 2023, the Department for Transport (DfT) published a consultation "Airport Slot Reform: a Consultation on Proposals to Reform the Airport Slot Allocation System" . The DfT sought views of industry stakeholders as regards proposals for change, with the aim of (i) stimulating a competitive environment by creating a more efficient, transparent and dynamic slot market and (ii) establishing a framework for the allocation of new slots. The consultation closed on 8 March 2024.
In August 2024, the DfT published the response by the Competition and Markets Authority (CMA) response to its consultation. In summary terms, the CMA gave a green light to proposed reform.
Major surgery or cosmetic tweaks?
The DfT consultation runs to 99 pages. The length alone is suggestive of fundamental reform rather than cosmetic tweaks. Three key issues that have long-time been the target of debate in the slots arena are grandfathered rights, ghost flights and secondary trading.
Grandfathered rights
New entrant carriers have long voiced concern over "grandfathered" or historic rights whereby an incumbent holder retains entitlement to a slot pair in a given slot season in perpetuity, subject only to satisfying an 80% usage minimum of the same allocation in the current scheduling season. Only if that usage minimum is not met, is the slot returned to the slot pool for re-allocation to other airlines, to include new entrant carriers (the "use it or lose it" rule). By DfT analysis, looking across all UK Level 3 airports, slots allocated through historic rights account for 92% of the UK’s total slots. Against the concerns of hopeful new entrants, incumbent carriers argue that historic rights provide much-needed certainty in terms of investment and business planning.
The DfT consultation proposes preserving the status quo for existing historic rights but advocates for a new approach to new slots only, " …we are proposing that for these new slots, Historic Rights would be limited to a fixed duration, after which slots would be returned to the pool for reallocation. Our initial view is that a set duration for historic rights of 15 years might be appropriate."
Ghost flights
The 80% usage minimum has remained unchanged over the last 30 years. This has seen the emergence of "ghost" flight operations by airlines i.e. flights without passengers, to preserve entitlement to allocation of the same slot pair in the next equivalent scheduling season. The consultation sought views (i) on the implementation of a higher usage ratio, to dissuade airlines from this practice, " to encourage more efficient and intensive usage of slots" and (ii) on whether a tailored approach is appropriate, allowing airports to take the decision to implement a higher usage ratio depending on airport specific circumstances.
The December 2023 consultation also proposed permanent powers to enable the Secretary of State to make regulations to provide specific alleviation from parts of the slot rules (to include usage minimum) "to provide a safety net for airlines where events take place which are beyond their control." The current fixed minimum usage requirement embedded in legislation does not allow for alleviation measures in response to unexpected events or circumstances. During the Covid-19 pandemic, in response to significant reduction in the level of air traffic demand, the UK Government introduced specific slot alleviation measures to support airlines [2]. The usage requirement returned to the 80:20 ratio from 26 March 2023. Those provisions were narrow in focus and did not have sufficient flexibility to respond to other, more recent events impacting on airlines and their ability to operate slots to satisfy the usage minimum eg the closure of Russian airspace following the 2022 Russian invasion of Ukraine.
Secondary trading
Whilst airlines do not have traditional property rights in their allocated slots, a buoyant secondary trading market has emerged that sees slots leased, swapped or transferred. Valuable consideration – often considerable – is typically part of the deal. Secondary trading of slots was sanctioned in the UK by a High Court ruling over a slot deal in 1999 [3] and remains a feature of the current slot allocation system in the UK. However, the existing legislation does not guide on the formal process for such trading nor does it provide oversight mechanisms and this has led to a lack of transparency. The consultation sees merit in the establishment of (i) a "clear legislative framework" for secondary trading of slots, (ii) a compulsory public slot register for each Level 3 airport which records the holder of historic rights to a slot, who operates the slot and the duration of any slot lease and (iii) a mandatory trading platform.
Aspirational goals
In high-level terms, the DfT identifies aspirational goals of reform, and the proposed means of achieving the same as follows:
- A more efficient slot system: through the removal of barriers to entry including a re-defined new entrant rule, the removal of restrictions on newly allocated slots, the removal of re-time priority, the introduction of permanent powers to improve resilience and an increase to the slot usage ratio.
- A more transparent slot system: by strengthening of the co-ordination committee role, the introduction of guidance on secondary criteria, power to direct the UK slot co-ordinator, a slot register - a specified platform for all UK slot trades and strengthened oversight of secondary trading, and limits on slot leasing.
- A different approach to the allocation of new slots: through the auctioning of new slots and ring-fencing of new slots for certain purposes. (A DfT commissioned report by CEPA considers two different auction designs - a combinatorial auction and a clock auction. The PAUSE (Progressive Adaptive User Selection Environment) procedure is advocated as an alternative model by others).
- A more dynamic slot system: to include fixed duration historic flights.
A first step
The Airports Slot Allocation (Alleviation of Usage Requirements etc.) Regulations 2025 (S I 2025 No. 158) which came into force on 13 February 2025.
The regulations amend the definition of "new entrant", increasing the threshold for airlines to qualify from those holding fewer than five slots per day to fewer than seven. The intention it to make it easier for smaller airlines to obtain slots at co-ordinated airports: as a "new entrant", a carrier benefits from greater priority when it comes to the allocation of airport slots from the slot pool. The revised definition also brings UK legislation in line with the Worldwide Airport Slot Guidelines.
Secondly, SI 2025 No.158 seeks to embed resilience into the system. It builds upon previous regulations which provided carriers with slot alleviation during the COVID -19 pandemic by introducing a permanent provision for air carriers to seek alleviation from slot usage rules where there are government-imposed measures relating to a pandemic, epidemic or other outbreak of disease, provided certain conditions are fulfilled.
Putting the UK on the front foot
The 2025 regulations are the first steps on the road to UK airport slot reform. The draft regulations were debated in the Grand Committee of the House of Lords on 20 January 2025. Lord Hendy of Richmond Hill, in commending the draft instrument spoke of it as, "putting the UK on the front foot…" in terms of being in advance of the European Union on both of the measure’s substantial subject matters. With those first steps accomplished, the more thorny areas of UK airport slot reform now need to be tackled.
[1] Cm9714 published December 2018 "Aviation 2050: The future of UK Aviation"
[2] The Airports Slot Allocation (Alleviation of Usage Requirements) (No. 2) Regulations 2021 Statutory Instrument and subsequent Statutory Instruments (the ATMUA Act)
[3] R v Airport Coordination Limited, ex parte States of Guernsey Transport Board, [1999] EWHC Admin 264
