Plane sailing.

Chek Lap Kok is the latest in a new generation of airports designed to be both easy and agreeable to use, and open to their surroundings. This approach to airport design, pioneered perhaps at Foster's Stansted, has been married to an east Asian fascination with size, and with the necessity of building in the sea, because of the very densely populated mountainous terrain, to create a complex as dramatic as it is convenient.

The airport is the twentieth-century building type. It may not, as some have claimed,(1) be our equivalent of the traditional city square with all its nuances and variety, but it is undoubtedly a vastly important component of the lives of most people, even in the poorest countries. And it is a measure of prestige. Cities and countries argue about which airport caters for the most flights, which has the best connections, which the most up-to-date facilities.(2) You are no one in east Asia if you haven't demolished a mountain and thrown it into the sea to provide buildings and runways which can be seen from outer space. Renzo Piano and Peter Rice started the fashion in Osaka (AR November 1994). Now, Hong Kong has caught up with Foster's Chek Lap Kok, which was opened on 6 July.(3)

The old Hong Kong airport at Kai Tak was dramatic to land on, with the 747s descending at an alarming angle among the tower blocks to bump onto a runway projecting into the harbour and the South China Sea. Now, a hilly island in the Hong Kong archipelago has been levelled to provide the flat surface for the runways of the new one, an area as big as the whole Kowloon peninsula. It is linked to the city by elaborate new road and rail links, slashing from island to island, which must have cost nearly as much as the airport itself. They ensure that the journey takes no more than 20 minutes. The whole complex is a tribute to the benign image that twentieth-century Britain (not entirely without reason) has had of the Empire, and is a rather late (and apparently initially unwanted) parting present to China after the Brits so appropriately sailed away on the decaying royal yacht last year.

It will become the biggest airport in the world. Its statistics are extraordinary, and do not need to be rehearsed here, where we are concerned with the building as architecture, function and experience. An airport must first of all work like a machine. It is a mechanism for processing us between land and air, and no matter how fine the spaces, how delicious the food in the restaurants, how dramatic the views, unless this basic function is properly catered for, the place will be a failure. A fundamental, simple plan is needed.

Foster has always held an image of one of the rustic American airports he saw in an Edward Hopper-like moment in his youth: a place where you come in from your car at the front door and see the planes waiting to take you to the heavens, and you walk straight towards them. His airport designs try to capture this immediacy. The effort at Stansted (AR Play 1991) was partly successful, but bureaucrats inserted screens to prevent through vision, and there was always the problem of having to take the little underground railway between the big building and the satellite, where you actually board your flight.

At Chek Lap Kok, a very much bigger building, Foster's ideal has come closer to realization. The essential movement diagram is very simple. You arrive either by car or train on the east side at the Ground Transportation Centre. Bridges convey you over a void into which you can glance to see the meeters and greeters welcoming arriving passengers. The whole awesome space is covered by parallel roof vaults which swoop slightly upwards west in your direction of travel, so that they constantly draw you forwards. Vaults are made luminous by ingenious continuous lanterns at their apexes which combine artificial and daylight(4) to make that favourite oriental colour, grey, dominate the atmosphere. Even to European eyes, greyness acquires a generous nobility in this building.

Roof vaults are curved steel shells, 36 metres wide. They curve longitudinally to give the forward thrust of movement and rise by some six metres in the middle of this curve. Each shell was assembled on site of components brought in from all over the world and was hoisted into place in one piece to rest on the concrete support structure. Here is the Stansted model resolved on a massive scale. The visual principles of being drawn from ground transport towards the aeroplanes are maintained (and you can here see the tail fins from the departures hall). Here again is the lightweight roof, carefully designed to be elegant and without wartlike cooling towers or other excrescences (it is astonishing how few airport designers think of their buildings as seen from the air).

As at Stansted, services, climate control and baggage handling are kept to an underfloor at the same level as the runways, and here the articulation in level of the Stansted satellite continues throughout the building, with arrivals at the first public level, and departures at the top under the magnificent welcoming roof. A very solid reinforced concrete base holds the roof down and clever joints between the two prevent the thin steel shells deforming or even taking off under stresses of expansion, typhoons and settlement. Such a thin roof in a tropical climate threatens to fill the spaces with almost steaming heat, as anyone who has stayed in an unreconstructed tin-roofed colonial bungalow can testify. At Chek Lap Kok chilled air is emitted from above the check-in stations and from what Foster's calls 'binnacles', independently standing service units. The heavy cool air forms a layer in which it is agreeable to walk and sit. Above is a layer of warmer air (to which molecules of the cool layer always aspire); the hot layer is supposed to hold the cold one down to some extent.(5) Here is an energy conserving experiment in internal climate control of huge buildings which may be of great importance in future - only carefully monitored measurement of the behaviour of the space will tell whether it works.

As you pass in the cooler air towards the planes, you can see out through huge glass walls with mullions made as bow-string trusses to the jagged blue skyline of the Lantau mountains and to the sparkling but turbid sea, and glimpse the giant bridges that connect the terminal to the heart of the city. This is a much more open airport than most, in which you scurry around in blind Kafakaesque passages, desperately following badly signposted directions.

At Chek Lap Kok you always know where you are. The swooping curves of the roof shells draw arriving people across the slender bridges over the void and past the check-in islands to the control desks and the east hall, which the designers proudly claim is the 'largest single international retail space in the world. If an airport can be likened to a city,(6) then this is its market square.'(7)

Beyond this area, the route continues towards the planes, under a vault similar to those that cover the departures hall, but now it is a sole vault, the stem of the Y-shaped concourse with its air-bridges to which the planes draw up. The two arms of the Y have vaults arranged in exactly the same direction as those you have already experienced, though here, for the first time, you find yourself moving across the axis, rather than with it. But by maintaining the direction of the vaults, you are always aware of the route and where you are in relation to the planes.

Arrivals are in an exact reverse pattern to departures, but a floor below. Just as at the Stansted satellite, arriving and departing people are never allowed to meet, though of course as you entered the complex you looked down from the bridges at arriving people. The travelators of the spine are reinforced by an 'automated people mover' (APM) in a tunnel(8) under the stem of the Y which provides fast connections in two-car trains between the arrivals and departures halls and the gates. The APM is designed to cater for the full traffic flows of 17,500 people an hour when the airport reaches maximum capacity in 2040. (I knew that I wouldn't be able to keep away from the triumphalist statistics for ever.)

But what matters about Chek Lap Kok is not so much the exact numbers of people, or tons of concrete, or acres of ground it covers, but that it provides an efficient, unconfusing and gentle way to move from land to air and vice versa. That it also has grand spaces, marvellous views and offers a sense of reassurance to the individual in the crowds surging to or from the planes make it a distinguished piece of architecture, rather than just a mechanism. It will never be a city, or a substitute for it, but it is a fine building. P. D.

1 Notably Deyan Sudjic in The Hundred Mile City (Andre Deutsch, London, reviewed AR January 1993)

2 Curiously, agreeableness and ease of use seem rarely to be discussed in the publicity.

3 With some teething problems of systems that were not the fault of the architects.

4 See p97 for a more detailed explanation of the lighting system.

5 Hot air is extracted by the binnacles at roughly the same height as the cold air is injected

6 A most extravagant analogy, for an airport is fundamentally a people processing machine. You have few possibilities for deciding where to go and for making up your own stories the discipline, quite rightly, drives you forward. There are few of the casual meetings that enhance life in cities - but I find that I bump into more and more acquaintances at airports these days. Such encounters usually lead to exquisite embarrassment, as both of us know that we can't escape from each other because of the nature of the process. You can't say that you are nipping off to see an aged aunt. Only Foster, who drives his own aeroplane, is free from such social catastrophes.

7 From a press release.

8 The baggage handling mechanisms are of course down there too.