The world’s airports are currently serving unprecedented levels of air traffic. In 2018, after 7 consecutive years of very strong growth, the roughly 4000 airports around the globe with commercial airline service handled some 8.7 billion arriving and departing passengers and 38 million landings and takeoffs1 2. These are all-time records that were unthinkable even at the beginning of this century – the number of air passengers has actually tripled (!) in just 23 years.

It is insufficiently appreciated that this traffic is very unevenly distributed, with the busiest airports holding a disproportionately large share. The busiest 40 airports (the top 1% of the 4000) served about 30% of the total number of passengers, and the top 100 (2.5% of the total) more than half (52%) of the total3. These huge facilities have by now become “engines” that literally move the world, enabling tourism, business travel, conferences and conventions, and the trading of high-value equipment and perishable goods.

The relentless growth in demand for air travel has placed a considerable strain on these critical airports, creating a nearly global “capacity crunch” both on “landside” (terminal buildings, access roads, and other facilities) and on “airside” (runways, taxiways, and aircraft stands). On landside, this has necessitated construction of new terminals and expansion of others, as well as redesigning and sometimes re-building entire access networks for cars and rail. The cost of many of these projects at the top airports now exceeds $1 billion per project and, in a few cases, $10 billion.

But while the landside capacity problem is difficult and extremely expensive to solve, the ultimate “bottleneck” is on the airside, whose capacity is typically driven by the capacity of the airport’s runways. These runways and associated taxiways and apron areas must be built on large swaths of land – often unavailable near big cities and in metropolitan areas. Worse, such projects require many years (at least a decade, typically) for approval and development, as they must address complex site preparation, environmental, legal, and, very often, political issues. The infamous “Third Runway” project at London Heathrow Airport has been on-and-off repeatedly for at least 50 years by now and it may well be another 10 or more before that runway finally becomes operational4.

There are three complementary approaches to addressing the airside capacity crunch. The first, and most obvious, is to invest in the building of new infrastructure – one (or more) additional runway and supporting airfield elements. The second is to increase the capacity of existing runways through improvements in the air traffic management (ATM) system – the modern name for what used to be called “air traffic control.” Finally, the third approach is called “demand management”, which means imposing a limit on the number of “slots” that are made available to the airlines or, in other words, on the number of movements (landings and takeoffs) that can be scheduled per hour at an airport. This does not increase capacity in itself, but reduces the incidence of traffic overloads and the attendant long air traffic delays at busy airports.

Of the three approaches, the first is the most effective in increasing capacity in one big step, but also the most expensive and, by far, the most difficult to implement. A new runway at an airport with a reasonably advanced ATM system will add between 35 and 55 movements per hour to the airport’s capacity5. The exact number depends largely on the types of aircraft that will use the runway and on whether the runway will be used for arrivals only or for departures only or for both. This increase in hourly capacity will, in turn, translate to increases of at least 20 million, and as much as 45 million6, in the number of passengers that the airport can handle in a year.

Capacity gains that can be expected from ATM improvements are more limited and happen at a slow pace over a period of time, as new technologies and procedures are introduced. At airports and countries that already operate advanced ATM systems, the capacity increases which we can hope for over the next 10 – 15 years are of the order of 3 to 8 additional movements per hour per runway7. Note, however, that this applies to all the existing runways – it is like all boats rising with the tide. Nearly all of the world’s developed nations are currently investing in improving their ATM systems. Most notable among these efforts are the NextGen program in the United States and the SESAR program in Europe – both with multi-billion dollar budgets over multiple years.

The third approach, demand management, is the easiest and least costly to implement. After all, the only action required is for a national government agency to determine and approve a specific limit on the number of slots that will be offered at an airport. But, if practiced extensively over many years, the approach will greatly interfere with airline competition by limiting the freedom to schedule flights at the times that passengers prefer and, worse, by making it difficult or impossible for new airlines to operate at the busiest airports as they simply cannot obtain any slots. Several of the most important and desirable airports in the world (London Heathrow, London Gatwick, Hong Kong, New York JFK, New York LaGuardia, Amsterdam, to name a few) have already reached this stage. At these airports, there are simply no good slots available for newcomers (or for incumbent airlines that wish to schedule additional flights): the few remaining slots are for times when people do not wish to fly – late night or early morning or Saturday evenings and Sunday mornings.

Different countries use different combinations of the above three approaches depending on their circumstances. For example, several countries in Northern and Western Europe cannot take advantage of the first approach, as it is nearly impossible politically to obtain approval for any new runways at their airports. These countries therefore use demand management to the hilt and hope that ATM advances will lead to marginal increases over the years in the number of slots they can make available to the airlines. On the other hand, many airports in Asia have built in recent years – or, are now in the process of building – additional airside infrastructure. In some cases, this is happening on an urgent basis, because planners failed to anticipate the need for such infrastructure. Hong Kong’s airport, for example, has essentially run out of capacity only 20 years after its opening in 19988. It is now building more capacity at great cost and complexity.

One of the first topics that SUTD’s Aviation Studies Institute will address in depth will be a critical review of the “airport capacity crunch” problem. The aims of the project will be to (i) assess the severity of the problem on a regional and, in some cases, local basis, (ii) evaluate prospects for relief, and (iii) speculate on potential consequences for the development of aviation services regionally and globally.

Peter Jackson is Professor and Head of Pillar, Engineering Systems and Design at SUTD and Director of the Aviation Studies Institute at SUTD. Amedeo Odoni is the T. Wilson Chair Professor Emeritus of Aeronautics and Astronautics at MIT and Distinguished Visiting Professor at SUTD.

  3. Airport Business (April 17, 2019), “Top 100 airports: preliminary passenger ranking 2018”. (Data compiled by Cirium Data Research Team.)
  4. The first study aimed to increase the number of long runways in the London Metropolitan area was performed in the mid-1960s; the hoped for time for the opening of the third runway at London Heathrow is the late 2020s, but many think this is optimistic.
  5. See, e.g., Chapter 10 in de Neufville, R. and A. Odoni, Airport Systems: Planning, Design and Management, 2nd Edition, McGraw-Hill Educational, New York, 2013.
  6. See, e.g., Chapters 9, 10 and 11 in above-cited reference.
  7. See, e.g., Chapter 10 in above-cited reference.
  8. The airport’s estimated (Master Plan of 2011) annual capacity is 420,000 movements; in 2018, it served 427,000 movements