Why do countries build domestic airport and international airport apart?

Question

This is the one that makes me wonder for a while.

Big countries' capitals often have two airports - one mostly for domestic flights, one for international flights. Tokyo has HND and NRT, Tehran has IKA and THR, Buenos Aires have EZE and AEP, Brisbane and Sydney have two different terminals from Domestic and International, separated by public transit ride.

Other countries don't have such system. In the USA, ATL or SFO or JFK serve both domestic and international flights and provide connections. In the EU, FCO or CDG do the same. In Moscow, all three main airports serve both international and domestic destinations to similar extent.

From the point of people living in the capital, it can make sense to put domestic airport closer and international airport further away. However, from the point of people living (or travelling to) outside capital, this would become a nightmare, since they have to waste a whole day on airport change, with a costly taxi ride or worrying about a shuttle that may get stuck in traffic. Even if there's a public transit ride between them that's a lot of inconvenience for somebody without local currency, with a lot of bags, etc, etc.

What was the historical motivation for such system? Is it still employed anywhere when building brand new airports?

Answer 1

It's usually history.

Cities very rarely decide to build two airports. Usually what happens is that a city built an airport many decades ago, sufficient for their flying needs, conveniently close to the city.

Over the decades air traffic expanded, and required a bigger airport. Often the city has also expanded, and it becomes difficult to expand the original airport, either because it is now surrounded by houses, or because the people now living near the airport don't want the increased traffic. So the city builds a larger airport further away.

Generally international flights migrate to the new airport because:

1. International flights require larger aircraft, which need the longer runways of the new airport.
2. The larger aircraft used by the international flights are noisier, and the residents don't want them at the nearby airport.
3. The fact that it takes longer to get from the new airport to the city is less significant if you've already taken a long international flight.
4. The newer airport can have better facilities than the old one, which major carriers like.

Answer 2

As far as having multiple separate airports within the same city, I watched a video on why London has as many as six different airports serving the city. Basically, it was because planes got bigger and noisier, and so it was necessary to demolish an older airport to build a newer one with bigger runways and newer facilities. DJClayworth's answer explains this in better detail.

As far as operating flights within a separate terminal in the same airport: one modern reason for doing so is operating cost for the airline. I can think of two modern examples:

• Austin-Bergstrom International Airport (Austin, Texas, USA) recently opened a new "South Terminal" that is completely separate from the main terminal. The South Terminal has no jetbridges; people board planes by stairs. Ultra-low-fare carriers such as Allegiant Air operate from this terminal, and similar carriers such as Frontier Airlines and Spirit Airlines have plans to move their operations there.

• Chhatrapati Shivaji International Airport (Mumbai, India) used to have all domestic flights run from Terminal 1, while all international flights ran from Terminal 2 (hence the local lingo "domestic airport" and "international airport"). Later on, Terminal 2 was rebuilt and replaced with a much-expanded terminal, which is capable of operating both domestic and international flights. The original plan was to demolish Terminal 1 and operate all flights in a single terminal, but low-fare airlines such as IndiGo still preferred to operate out of Terminal 1, which is why it still exists (though parts of it have been decommissioned).

In both the above cases, both terminals can't be accessed from the same access road; you need to drive outside the airport property to access one from the other. Both of the low-cost terminals (Austin's South Terminal and Mumbai's Terminal 1) have a significantly lower operating cost for the airline than the main terminals. For instance, not having jetbridges costs the airline less than having jetbridges (though Mumbai's Terminal 1 does have some jetbridges; very few flights use them). The savings are often passed to the consumer through lower fares.

Most of the time, these low-cost terminals lack the necessary immigration and customs facilities needed to support international flights. While the U.S. does not have exit immigration, it still requires incoming international passengers to pass through entry immigration and customs. (In some cases, these checks are done at the origin airport; this is why U.S. airports that ordinarily only have domestic flights can also have flights to preclearance destinations.)

Answer 3

One idea that I had during writing this answer:

Of course you end up having domestic flights from the "international" airport, too. You can charge more for those flights, while subsidizing flights from the "domestic" airports. This way you can have cheap flights around the country, while making international travellers to the rest of the country foot a large bill.

Sounds like something that looked like a good idea in the 60s or so, but now is actively harmful because it starves inner regions for tourists and business travellers, incentivizes everyone to move to the capital/largest city, which is something most countries try to avoid these days.

Answer 4

If your city has two airports, typically one of them will be "better" than the other - e.g. more convenient to the city center, more modern facilities, etc. So without any restrictions, traffic would tend to gravitate toward the better one. Then you don't really have the benefit of two airports - the better one is overcrowded, and the worse one sits underutilized. Traffic isn't divided between them in an efficient manner.

So you may want to have a rule that forces both airports to be used. And one simple such rule is to declare that one airport is only (or mainly) for international traffic, and the other for domestic. This has the benefit that travelers can know immediately which one they should use.

Of course it has drawbacks too, as you have mentioned.